Transcripts
1. 1.1 Introduction: Hello, my students and welcome to acoustics. 101 My name is Mario is and I'll be your instructor throughout this course. The main purpose of this course is to teach you how to design your own speaker enclosure. This will be done using two methods. First method by doing some mathematical calculations, but with the help of an Excel spreadsheet and second, with the aid of a simple and cheap piece of software, you will get the Excel spreadsheet with the formulas, and the base reflects alignments. Table for free if you want a little more convenient. Since the mixture features, you can buy the enclosure design application mentioned earlier. However, this is completely up to us. Both methods yield the same results. To get the fun part of designing enclosures, which will be at the end of the course, we will have to cover some basic stuff about the acoustics, how sound waves work, how the speaker is designed in its characteristics and closure types and some other audio stuff. In my opinion, explaining these topics is essential for truly understanding how an enclosure works and how to design it properly. Even if you feel you're confident in your level of understanding acoustics. I advise you not just keep till the end as I'm sure you will discover many new things which will help you along the way. This course is designed for audio files in the eye wires who want to extend their knowledge about sound waves in speaker systems. If you want to understand how sound works and how to design your own speaker enclosure, then you have come to the right place. Hope you will enjoy learning from this course as much as I enjoy creating it.
2. 1.2 Contents: Okay, so let's give a complete rundown off. What should you expect from this course? First, I'm going to talk about sound waves. We are going to see how they work from a visual perspective and from a mathematical perspective. Then we shall move to the sound wave characteristics, amplitude, frequency and wavelength. I'm going to dedicate a separate lecture for the fourth characteristic face because it's a bit difficult to comprehend, and it's important for what's to come at the end of this section. I'm going to use a signal generator and an oscilloscope to show you in real time how amputated frequency change. Hopefully, this will clear things up even more. In the next section, we will focus on speaker design. I'm going to list all the components of the speaker, described their function and show you the basic principles off how they indirect with each other to produce some. After that, we shall move onto frequency response charts. These charts are something you need to get really familiar with, and there are certain expects. I want to cover and explain some audio terms because we will use them later on in the course. Next we have the field. Small parameters. We all know the big list of parameters that we find in the speaker's specification sheet. They might be intimidating and confusing, but in the end, I'm sure everything will be crystal clear. Next section is about how sound his measure in the visible scale. It's important to understand how sound his measure, because this ball scale is not linear and has a certain particular aspects that needs explaining. Then we shall move onto enclosure types. I will list the most common enclosure types and give a brief explanation about each design , the pros and the cons. I will cover five enclosure types the infinite baffle, sealed or closed base. Replace reported band pass in transmission line. Next, we got a complete section dedicated to the sealed enclosure. This type of an enclosure will be covered in great detail, and I will show you how to design one properly. After that, the second type of enclosure, which I will cover in great detail, will be the base reflects. This is probably the most widely spreading closure out there, a bit more complicated than sealed, but nothing to worry about as I will cover all the principles behind it and show you how to design one specially tailored to your application. Finally, I'm going to give you some construction tips. While I'm not going to show you how to physically build the enclosure as this can be done by anyone with wood working skills, I'm going to give you some building advice and techniques that are relevant when constructing the box like a panel. Dimension ratios, speaker placement, port placement, bracing techniques, how to reduce panel resonances, careful design. And so on. As of November 2017 I had did the first update toe this course here. I'm going to show you an example of how to build a two way bookshelf speaker. In addition, I will explain the basics regarding crossover networks and show you how to build a simple one. Don't expect high end crossover design. We will leave that for a future course, just a basic to weigh filter. Now that we got all the contents covered, let's dive right in
3. 2.1 Sound wave visualization: before we start to define the sound wave, let's begin by visualizing it. The most widely spread example is toe. Picture the ripples in a lake. If you throw a rock in the water, you will create the some reports that will go into all directions, starting with the point where the rock touches the water. So the point of impact coincides with the sound source, and the water waves mimic the sound waves. This is a nice way to see sound toe. Visualize it. But this example is partially correct because it gives you a two D representation of how things actually happen. You only see the ripples expanding on the horizontal plane. However, sound goes into all directions, they say. I tap my fingers and produce a sound. It doesn't just go on the horizontal plane. It goes into all directions. Think of it like a sphere like like an expanding sphere. You can see in this image the yellow spot is the sound source, and the sound is going to into all directions, not just the horizontal plane and progressively losing amplitude. The volume decreases as the instance increases from the spot where the sound was originally created.
4. 2.2 How sound waves are created: know that we have a visual reference. We can go more in depth on how they are created. So basically the somebody's are created when there's a pressure difference in a medium, and the medium can be guess liquid or solid. If there is no medium, some cannot travel. So that explains the phrase no one can hear in space, because in space there is only void and sound cannot travel in void. Now let's let's focus our attention. Toe a speaker, see how the speaker produces sound. How how it produces a pressure difference. Well, the pressure difference comes from the cone movement. The corn moves very fast, and it disturbs the air particles in front of it. So creating this this this pressure in front of the comb. So because of this, the air molecules in front of the speaker will start to vibrate. This vibration will trigger the air molecules in the immediate proximity to vibrant as well , and this pattern continues until all the energy from the sound is depleted. You have to understand that the air molecules in front of the speaker maintained their position. They are passing along the vibrating motion to the molecules in the vicinity. They are not inherently moving. Don't don't confuse sound waves with wind if the molecules in front of the speaker move all the way to the far end that he's actually wind. So try not to confuse wind with the sound waves. When the speaker is moving, it actually also lates from its resting position. It will go backwards as much as it will go forwards. This will create points off negative and positive pressure. For this reason, the air molecules will form a pattern off high density, where the molecules are tightly packed in portions of lower density, where the air is more rarefied this better and will transfer to the molecules in the close vicinity. And this goes on until the the energy is depleted. This pattern is in direct sync with how we visualize the way from a mathematical point of view, the peaks correspond to the points off high pressure, and the dips suggest the points off low pressure
5. 2.3 Sound waves characteristics : Amplitude, Frequency, Wavelength: Now that you've got the preview of the mathematical representation of the sound wave, let's use there to explain the sound of characteristics. There are four important ones. Amplitude, frequency, wavelength and face. I will briefly cover the 1st 3 because they are the easiest to understand and leave praise for the end, the because I want to explain it thoroughly. Now let's switch to the mathematical representation of the sun We've and tried to go from here. You have, ah, time on the X axis and pressure on the Y axis. Now we learn from the previous listen that this sine wave is describing the cone motion. The peaks described the points off high pressure. So when the cone moves forward and the dips described the points of low pressure or when the cone moves backward so higher amplitude will mean ah, higher sound pressure and give you on example. Here is a low amplitude sound wave, and here is a high aptitude sound. Wave Frequency describes the pitch of the sound and represents how many complete cycles the sound wave makes. In a second. High frequency sounds will have more cycles per second and low frequency sounds will have less cycles per second. Frequency is measured in hertz, so if a sound wave has 100 hertz, it'll make 100 cycles in a second. Now let's give an example. Here is ah to hurts wave so you can see the time axis. In one second you get two complete cycles. Here is one cycle and here's the other one. Now here is an example of a sound wave with the frequency off four hurts, so this one makes four complete cycles in a second regarding the frequency characteristic. What is relevant to know is that the human has a fixed hearing range, so the human hearing spans from 20 hurts all the way to 20 kilohertz. So that's why we don't hear a dog whistle, for example, because it operates in a frequency which is above 20 kilohertz, which is also called ultrasonic. So the dog has a hearing range from 60 hertz 2 44 kilohertz so we can hear sounds which are much higher in frequency. Now, on the other end of the spectrum, you've got the elefant which can hear way Bill 20 herds. These frequencies are also called for sonic. These very low frequency sounds are used by elephants to communicate over long distances, but we can't hear these sounds at all. However, we can feel them now. Let's move on toe wavelength. So if we switch the X Texas to distance, the wavelength is the distance between two points, which have the same location on the cycle. This is one example. This is another. This is another. So, of course, even if you start from the beginning, one complete cycle equals exactly one way bling. Because of this, the way bling is in direct correlation with frequency, and it's calculated by using this formula. Lambda is the symbol for wavelength, and it is equal toe 343 divided by the frequency of the wave. 340 free is actually the speed of sound in air measure the in meters per second. So let's calculate the wailing for some sound waves with different frequencies. If you calculate for 20 hertz, for example, the wavelength is 343 divided by 20 which is 17 approximately 17 meters long, 400 hertz, its 3.43 meters, and for higher frequencies like, let's, say, 5000 herds you get the shorter wavelength off 6.86 centimeters, and for the top of the hearing range 20 kilohertz, you've got only 1.71 centimeters. As you can see, the lower the frequency, the larger the wavelength is. In other words, base has large wavelength now, depending on the length of the wave, it will interact differently with the environment. If the waving counters an obstacle, depending on the size of the object and the length of the wave, it can bounce off of it. Or it can pass right through it or a combination of both. If the object is made from a certain material or has a certain shape, it can observe the wave or part of it. So let's give an example. If the object is 10 times smaller than the wavelength off that particular frequency, the wave passes food like there is no obstacle. So let's give an example. In this case, if the frequency is ah 100 hertz, then the wavelength is 3.43 meters. Any of the object is, ah, 34 centimeters across. Then the wave will pass like there is nothing in front of it because the object is to small compared to the size of the wavelength. No, the other way around. If the object is at least have the wavelength in size, the wave will reflect. So let's see, We have the same object off 34 centimeters across. But now we have a frequency off 500 hertz, which has a wavelength off 68 centimeters. This wave, when it will encounter the object it will reflect because the object is is of considerable size compared to the size of the waving. Now you have to realize that these are some basic guidelines. In reality, the process is much more complex, and usually there is a combination of reflection passing through absorption. But this is just to get the general idea of what happens to give you a real world example. Let's imagine you're standing in a queue to go inside the nightclub. Know when you're standing here. You're actually hearing the sound coming from inside, but you only hear the base, so you hear some beats, but nothing more. You only here the low frequency sound ways that this is because base has a long way. Billings off 10 meters and even higher. So when they encounter the walls, which is an object of considerable size, they can pass through it. And some of the ways escape to the outside so you can hear it. The higher frequency just bounced around when they meet the wall, so you don't hear them from outside. As soon as you will enter the club, you will get the Russia vocals and high frequency sounds that you didn't hear from the outside.
6. 2.4 Sound waves characteristics : Phase: the last sound wave characteristic we need to talk about. This face faces a position of a point in time on the cycle of the sound wave phase is measured in degrees from 0 to 360. You can also use radiance as a unit of measurement, but degrees are most often used now. I know you're confused by now, but keep watching because it'll get better. Let's take a look at the mathematical representation of the sun leave. One complete cycle is from here to here. The beginning marks the point off zero degrees in the end march, the point off 360 degrees face. If we take different points in the cycle, we will have different face values. So in the middle we will have 180 here. We're gonna have 90 degrees phase and some random point in the cycle. Here we will have 220 degrees face. You're probably wondering ways this important ways ways phase, something to consider phase. It's actually really important because when new sound waves collide, considering they have the same frequency, they will add or subtract, depending on their face. Let's see what happens when two waves with zero degrees phase meet up. Now, in the examples which are about to follow, we will add up to sound waves. These sound waves will have the same frequency and the same amplitude. To keep things simple. You can see on the bottom, I said, the phase zero plus zero. It doesn't make any sense mathematically, but it's easier to comprehend this way, so you can see in the top. We have the first wave in the middle. We have the second wave, both with the zero degrees phase and on the bottom. We have the some off the two waves. The amplitude off the two waves will combine and will form a wave which has double the amplitude because the two waves are in phase. If we draw a line here, you can see that the amplitude is one. And on the second wave is the same because they are in face and when they add up, they have ah, amplitude off to If we draw another line er on another section of the cycle, you can see that here they have ah, zero amplitude. So they combined for on amplitude off zero now Let's see what happens if if the second wave is out of face. If both waves have the same face, we say that the waves are in phase. But if they have different faces, like in this example, the first the wave has zero degrees phase and the second has 90 degrees face. We say that the second wave is, ah, 90 degrees out of phase relative to the first wave. So let's see what happens when they meet up. If we draw a line on this section, we can see that the first wave has an amplitude off one, and the second wave has an amplitude of zero, so they add up to a combined amplitude of one. If we draw a line on another section like over here, for example, we can see that the amplitude zero plus minus one. The amplitude is minus one. Now what's important note here When the waves are in phase, like in the first example, they add up to double the value. When the waves are 90 degrees out of phase, we can see that when they combine, they form or a sound way, which is a bit higher in amplitude, so if we look at the peak values we have Ah, 1.4 and the on the dips we have minus one point for. So the combined wave is, ah a bit higher in amplitude. Now let's see what happens when they are 180 degrees out of phase. This is sometimes called anti face. Now what happens here when the amplitude zad up because they are in reverse phase or 180 degrees out of phase, they add up to zero. There is no sound. So if you draw a line here, we can see that the amplitude is one on the first wave on the The amplitude on the second wave is minus one. So they add up to zero. If we draw on over here, we have zero plus zero equals zero. If we draw a line over here, we have minus one plus one equals also zero. When the waves are 180 degrees out of phase, they will cancel each other out. No, let's take a look at some real world examples. So let's say we have a speaker which is not in any enclosure. Just a speaker in free air and let's see how phase is actually a big deal over here. Like we said earlier, the speaker oscillates from its resting position, so it will go backwards as much as it will go forwards. In conclusion, when the speaker moves, it's great sound in the front, but also in the back. So when the cone is moving forward, it creates positive air pressure in the front of the cone and negative air pressure in the back of the court. Alternatively, when the speaker is moving backwards, it will create negative pressure in the front. I'm positive in the back when the speaker is creating sound in front of it. It creates the same sound in the back, but they are 180 degrees out the face. While high frequencies don't suffer as much from this since they have very short wavelengths base. His severely affected back waves travel to the front of the cone, and the cancellation occurs since they are 180 degrees our face. That's why when you play music through a speaker and you hold it in your hand, there is virtually no base. That is the main reason why speaker are placed inside an enclosure to separate the front waves from the back waves. The back waves are trapped inside the enclosure, and they cannot meet with the front waves toe achieve cancellation. Now let us move to another example where phase is something to worry about. Here is a two way speaker you have, Ah, Tweeter and a meat based driver. Because of the positioning of these two speakers, they are some degrees out of phase. You're probably seeing what he's talking about. They are on the same careful, but actually the sound comes from the acoustic center off the speaker, and we convene that the acoustic center of a speaker is in the place off the voice coil so you can imagine the twitter is way in front and the voice coil off. The meat based driver is somewhere around the magnet area, so actually the Twitter is in front of the mid based driver. Let's draw the sound played by the Twitter, and here is the mid bass driver. You can see that there is a phase mismatch. If we draw a straight line between the two, we can see that they are clearly out of face. I don't know exactly how many degrees out of phase, but they are out of phase now. While the Tweeter in the mid based driver don't play the same frequency range at the crossover region, they have a small band with where their frequencies overlap. So in that particular area, there might be some phase issues where some cancellation occurs or the waves reinforce each other too much, and it's tool out on that frequency region. And that might be an issue. Now there's, AH, fuel solutions to this problem. You either completely ignore it. The phase issue is not causing much problems, depending on the particular speakers you have and crossover region you choose, or you use the some of these methods you can use an asymmetrical baffle. This way, the acoustic center off the Twitter is aligned with the acoustic center off the mid based driver. So when you play sound through the twitter in the mid base, they are in phase and the problem is solved. Another solution. You can use the slanted bear full. This is an incline, the careful. So actually the Twitter is somewhat behind the mid bass driver and the acoustic centers are aligned and another solution, and the more complicated one is in the crossover design to use ah leather delay network. This way, the Twitter is in the same position on the baffle, but it received the signal a bit delayed. So when they both fire they, they are in face. Another example of ah, phase mismatch issues is in a car. Now you can see in this example there are a lot of speakers in the car, but let's focus on the base drivers from the front doors, this one and this one. So when you wire the speakers, let's say you bought some after market speakers and you replaced the O am ones. But when you wear them up, you accidentally mismatch the polarity. So you wired the one from the left correctly in the one from the right in reverse polarity . Now there is nothing inherently wrong with wiring the speaker in reverse polarity. The only issue is that when the speaker moves, it starts its motion by moving the cone backwards and then moving forwards. So actually, the speaker from the right will be out of phase 180 degrees out of phase with the speaker on the left, so a lot of cancellation will occur and you will basically have no base in this car. To get around this issue, you have to reverse the wires off either the left or Ah, the right speaker. It doesn't matter how you wire them as long as they are wired the same way, so they are in face.
7. 2.5 Real-time analysis of sound waves using a signal generator and an oscilloscope: Okay, So he we're gonna have a practical example regarding the sound waves so we can better understand them. We will focus only on the amplitude and the frequency. So basically, we have ah, signal generator so we can generate anyway for me, like off whatever frequency in whatever amplitude, we also have an oscilloscope so we can view the way form. And in real time we're gonna just the amplitude and the frequency and see how they change and how the sound. Because we also have a speaker connected to it. And you will also hear the frequency and how loud or how quiet it is. When I will do some modifications, I will let you hear the sound. But after that, I will aided the audio out because it will get really annoying to have a continuous beep in the background. So let's start by he firing up the generator. I'm going to use higher frequencies because not all audio systems can play low frequencies . So let's start with the 100 hertz. You're gonna look at the screen and you're gonna tell me Hey, this is to hurts. This only two cycles 100 herds is 100 cycles in a second. But if you look closely at the graph, each division means to milliseconds. So if we count each division, we have five on each side. So 10 divisions from the start to finish this means 10 multiplied by two milliseconds, 20 milliseconds. So we have two cycles in 20 milliseconds. If we go all the way up to one second, we have 100 cycles in 1000 milliseconds, so you get the idea. Okay, so let's suggest the amplitude in there. We have my understand Let's go toe minus 20. You can hear now that the sound is quieter because the way form has lost amplitude in the other way around. We can go higher in amplitude. Let's say we go toe minus five. You can see how much higher the amplitude is and how louder the sound becomes. If we adjust the frequency, let's say we go to 500 hertz. You can see that they're more cycles per second. Last time we had to cycles in 20 milliseconds. Now, if we can't, then we have 12345 James cycles and cycles in 20 milliseconds. That means 500 cycles in 1000 milliseconds. If we go to 1000 hearts way, get even more cycles per six and you get the idea. So now I hope you understand even more how frequency and how amplitude works now that you saw them, how they affect the sound in real time.
8. 3 Speaker design: Hello, guys, and welcome to the second part of this course where we're going to talk about the speaker design. Now I will identify each component of the speaker and explain what's what in the purpose, off each component. But before we take the speaker apart, it's better if you understand the basic principle on how the speaker works and how it is producing sound. At its core, the speaker is basically a motor with the best in attached to it. The motor is making on up and down motion or right left, however you see it, and the business is following that motion since it's attached to the motor. So basically, this makes the speaker a transducer. These means it transforms a type of energy into another type of energy. So actually, the speaker transforms on electrical signal so on electrical energy into a mechanical energy because it says the cone in motion, and furthermore, the mechanical energy is transformed into a critical output. The transformation is the two step process. Because of this reason, the efficiency of the drivers are very, very poor. Now let's head over toe a speaker cross sectional diagram and tried to explain the different components and how they interact with each other to produce sound. So the speaker is made by three main parts. The motor, the suspension and the diaphragm. When I will talk about the various components of the speaker, I will point the mount into both the diagrams you see over here so you can understand better their location. Now let's talk about the motor system. The motor is composed by the front plate, the back plate. The magnet, which sits in between the poll peace and the voice coil. The front plate, back page and pull peas are usually made from iron or some other material that provides a path for the magnetic field off the magnet, all of them sandwich of the magnet. Together, between the front plate and the whole piece, there's a little gap. The gap is very small and allows just enough room for the voice coil to travel through it. Unrestricted Inside this gap between the front plate and the whole piece, there is a very intense magnetic field. When an electric current passes through the coil, it becomes an electro magnet and creates a magnetic field which interacts with the magnetic field of the permanent magnet because of how the voice cool is attached. It can only move up and down, since the electrical input will be alternating current. It's which is polarity many times per second. So if the voice score is moving up as a result of repelling with the magnet field off the permanent magnet, when the polarity will change, it will go down as it will attract with the magnetic field off the permanent magnet. This happens because the electrical input is a see if it would have bean d. C. The coil will movinto one direction up or down, depending on the polarity, and just stay there. No weapon down motion. No, let's move on to the diaphragm. This is made by the cone and the dust cap. The cone is a defining factor when it comes to the speaker characteristics. Ah, good quality speaker has a cone that is both light and rigid to reproduce high quality sound. The cone is to be perfectly stiff. In reality, this does happen at lower frequencies, but as soon as we go up in the frequency range, the co stars to bend and flex, causing irregularities in the frequency response and the high frequency efficiency of the driver. This is called Cone Break up. I don't know how to explain this. Better try to imagine. Imagine that little parts of the cone start to vibrate as well, creating many speakers inside the speaker. Usually, the result of this is having a boost in high frequencies, which most of the time is not desirable. To reduce this break up, the cone is made from all kinds of materials to ensure that it is both light and rigid. The most widely spread materials are paper, aluminium, Kevlar, maybe expensive materials like beryllium or some weird ones like bamboo or banana. Now let's move on to the dust cap. You might think that the little bump in the middle of the cone is actually part of the coun , but it's not. The voice coil is attached to the corn and then place between the front plate and the poor . Peas, also known as the Gap, realize that this gap is made as narrow as possible on Lee to let the coil move on, restricted after the cone is in place. The part of the gap between the pole piece and now the voice coil. He's exposed to foreign particles, mainly dust sees. The space is so narrow, this can be an obvious problem and cannot be ignored. To fix this issue, a seal has been placed on top called the Dust Camp. Now let's talk about the last section off the speaker. The suspension. The suspicion is made by two things. The surround in the spider. The spider is that yellow looking accordion right about the voice school. The main purpose of the spider is to keep the voice coil centered over the pole peas and keep foreign particles away from entering the gap. Also, the stiffness off the spider is very important as it determines the resonant frequency off the driver. This around connects the exterior part of the cone to the basket or frame. The surround has two main purposes, helps to center the cone and keeps the voice coil inside the gap. It also provides a restoring force for the speaker, but not as much as the spider. Now you have a basic understanding on how the speaker works. This would be off help when we're gonna talk about the feel small parameters, and also it gives a better view on how things work in an audio system
9. 4.1 Frequency response charts: Welcome to the third part of this course where we're going to talk about the frequency response charts and explain some terms. So this is a frequency response chart. Nothing very fancy. We got the frequency on the X axis, and we got the magnitude on the Y axis measured in a decibels. Usually the frequency is spanning from 20 hertz to 20 kilohertz, because that's the hearing range. But sometimes, and in this case, also it is measured down to 10 hertz because while we can't hear that the frequency, we can feel them now. What's important to know about the Y axis where we measure the magnitude in disciples, is that the values which are shown there are not absolute values. This means if I let's say, I want to read how many disabilities we have at 40 hertz, we got 100 disability. But ah, that is not the case. You cannot have an absolute value on 40 hertz. That depends on how much voltage you feed to the speaker. So the volume on the amplifier, the efficiency of the driver and many other factors. But what is important is the relative values, so we know that 40 hertz is quoted at the 100 decibels. But if we take another frequency, for example, Ah 100 hertz. This is quoted at 94 disciples. So from this weekend, deduct that 40 hertz will be six decibels louder, compared 200 hertz. What's important to know is that this proportion off six disciples will maintain even if we lower or increased the volume. So let's see if we have ah, 120 decibels absolute value at 40 hertz. We know for sure that at that 100 hertz, we have 114 so six decibel less. Another thing I want to point out at this chart is that the frequency access is not linear . It's logarithmic, so you can see that each division is marked by the previous one times 10. So you've got 1000 1000 10,000. The next one would be 100,000 and so on. And in between these division, you have little lines that mark the subdivisions. So between 101,000 herds, we have 203 100 400 so on. Now they know that we got this cleared up. Let's move on to some other examples of frequency response charts. Now let's take a look at an example off linear frequency response. So in this graph, you can see a lot of lines. But ignore the blue one, that is. Ah, the impedance and the green and the red line represent the frequency response off. Access 30 degrees in 60 degrees. Just focus on the black line. That is the only access frequency response. So this is a mid range driver, and we are interested Onley in the mid range frequencies because you can see it loses linearity in the upper frequencies and in the lower frequencies. But that is not our focus. So let's try toe, analyze which part of the graph is very much linear. We can see that below 200 hertz. The response starts to roll off so below that the response is not linear and also above 4000 hurts. Their response. Stars Tau go up abruptly so it loses linearity so we can say that the the Speaker plays linearly from 200 herds to 4000 hertz. This is a linear frequency response. Now let's take a look at the nonlinear frequency response charge again ignored the impedance chart and the red and green graph lines just focused on the black one. This is a twitter, so we're interested only in the high frequency response from, Let's say, three kilohertz and above the frequency range from 3000 herds all the way to 20 kilohertz, and we can see the response is somewhat linear. Up until 7000 Hertz and then it starts to dip from 7000 hurts all the way to about 11 kilohertz, and then it starts to rise again so we can see that this response is clearly not linear. If we take a look, another example of a frequency response, we have the no. Basically, you will see this response in a two way speaker, and the black line represents the overall response of the speaker, with the two drivers wired correctly. But if you tinker with the crossover and wire the speakers in reverse polarity, you will have the speakers playing in 180 degrees out of phase in the crossover region. So let's see, in the crossover region where the frequencies of the two speakers overlap, they will cancel each other out, so you will see a big dip in the frequency response. Call them. No, this is a nice way to check the crossover frequency. So you can see in this graph the crossover frequency between the two drivers is somewhere at, ah, 1800 hertz. Now let's move on to another type of frequency response chart. The co owner break up. So we talked about before the cone break up. When the speaker reaches higher frequencies, the cone starts to bend and flex. It loses rigidity, so it starts toe alter the high frequency response. And you can clearly see this in this chart. The speaker plays somewhat linearly from ah, 100 hurts all the way to 4000 herds. But then it started to get the southern rise in high frequencies. This is because the cone is breaking up. When you see this anomaly in the frequency response chart, you know that it is a cone break up. So when you are choosing the crossover point for this type of speaker, you know that you have to choose it way below the cone break up. So here the cone is breaking up at four kilohertz. You have to choose the crossover point at least two kilohertz or lower
10. 4.2 F points: Okay, so now let's talk about some terminology regarding these frequency response charts. So I call these the F points. Here's a frequency response chart. Again, disregard the impedance chart and focus on the black line, which is the actual frequency response. So if we draw a horizontal line to mark the linearity off this response, we can see that this is achieved that 98 decibels. Also, if you look at the response, we can see it starts toe roll off at the lower frequencies, starting with these point at around 160 hertz. This is also called the F zero point where the response starts toe degrade as we go lower and lower in frequency. Another point of interest is three decibels below this line. So 98 decibels minus three. We're at 95 decibels, and this point is actually at ah, 88 hurts. This is also called F three. So f free in this case is 88 hurts. This point is relevant because we convene that most years. I cannot hear the difference off plus minus really be. Of course, they are all the files out there that will tell you they can hear the difference off 0.5 decibels or whatever. But this is accepted as a general rule that, ah, variation off three decibels is not something that we pick up so easily. So when you're looking at this response, you are going to say that this speaker plays linearly from 1000 hertz all the way down to, ah, 160 hertz. But when you look at the speck shipped from the manufacturer, the frequency response will be quoted down to 88 hurts so down to the F three point. So it is generally accepted that the responses linear all the way down to the F three point . Now, another point I want to talk about is the F 10 point. This is 10. This was below the linear response line. So 90 decibels minus 10 we got 80 decibels. So this point represents 57 hurts. So the F 10 point is that 57 hurts. Why is this point important? The F 10 point is also relevant because 10 decibels is considered to be twice as loud or twice is quiet when it comes to perceived loudness. So from the F 10 point downward, there is nothing of interest because everything is at least twice as quiet as the rest of the frequencies and therefore are covered by them. Anything below F 10 is barely terrible.
11. 4.3 Octaves and roll off slopes: Okay, now that we got the f points cleared up, let's talk about octaves. On Octave is a frequency span from an initial point to double that value. So to give an example, 20 hertz to 40 hertz, that's an octave. Another example would be 1000 herds all the way up to 2000 hertz. That is another active. So basically any doubling the value is an active Give it weird example. 1337 hurts all the way to a 2674 hurts that is also on active. We can also reverse that. So if we say one octave below 200 hertz, there is actually 100 hertz. And to give you another example, if someone would say this midrange needs to play at least three octaves and should be crossed over that 200 hertz. So if the mid range needs to be crossed over that 200 hertz, it means it has to play from 200 hertz and above. So, uh, if it should play at least reactive, this means that the first active will be 200 hertz till 400 hertz, the second octave would be 400 to 800 the 3rd 1 would be from 800 to a 1600. So the mid range will have to play from 200 all the way toe 1600 hertz. Now let's talk about roll off and slopes. When you look at the frequency response of a speaker, you will see that the response starts to roll off, either at the ends because the speaker has reached its physical limitations or there is some kind off electric filtering, or kristic filtering that forces the speaker response to roll off. Now the response can roll off at a certain pace, this pace or steepness of the slope he is measured in this bill's prerogative. You will hear something like, uh, 12 disbursed for octave or 24 disciples, Poor octave or six decibels Proactive. So to give you an example, I have here a chart which has two responses, which is start toe roll off at the lower end of the frequency spectrum. The blue one rolls off at the 12 disciples productive, and the red one has a steeper slope off 24 disciplines. Proactive so we can see at the blue response, it starts to roll off with 60 hertz, which is at 90 decibels. So one octave below 60 hertz is at 30 hertz. So since the response rose off at the rate off 12 decibels for active at 30 hertz, the magnitude should be 90 minus 12. We should be 78 disciples. So if you go even lower, so on octave lower at 15 hurts. We will lose another 12 disciples. So 66 decibels so you can see that this slope describes the rate at which the speaker is losing amplitude as the frequency decreases. And now if you take a look at the red, the response curve which has a slope off 24 decibels proactive. We see that again. The response starts to roll off at 60 hertz, and we have, Ah, 93 disciples now. So since it's losing 24 decibels proactive at 30 hertz sewn octave below 60 hertz, we should have 93 minus 24 which would have 69 decibels. And if we go in octave even lower, so at 15 hurts, we should get 69 minus 24. So 45 decibels, usually these Rohloff slopes indicate the transient response of the speaker, so a steeper slope will have Ah, slightly worse transit response and a more smooth slope will have a better transit response , but more on this later on.
12. 5.1 TS Parameters, Fs: Welcome to the fourth part of this course. We will talk about the feel small parameters when people say feel small parameters, they usually mean this big list of parameters from the spec sheet of the speaker, which is somewhat correct. The feel small parameters or T s for short are actually small signal parameters. The rest are large signal mechanical parameters, etcetera. What I'm trying to see is that to design a speaker enclosure, you actually need only three parameters. This this and this While you only need these three values, I'm going to cover the majority of them some briefly, some extensively, because I don't like it when you have a narrow picture off how things work, some might ask, What's a feel? Well, there actually names I never feel. And the Richard Small. Basically, Mr Thiel wrote a paper about various parameters that affect the performance off infinite baffle and base reflects loudspeakers. Mr. Small completed the paper after some time. Of course, many others have their contribution. But these two guys are the ones who got the most credit. Thus the name. Now that we got the general stuff covered, I'm going to start with the three important ones. We get the FS or resonant frequency, the cure quality factor, NVs or equivalent compliance as a volume before I get to ves. I'll have to explain CMS beforehand because they are interconnected. FS is the resonant frequency in free air and it's measured in hertz. It is the frequency where the driver moves with minimal effort. If you tepe speaker or any object for that matter, it'll produces sound, which has the same frequency as its resonant frequency. What's important to know is that when the driver reaches the resonant frequency, its response starts to roll off. So if we look at the frequency response chart, we can see that the driver is playing fairly linear. Then it reaches the resonant frequency and then the response starts to degrade and roll off . A speaker cannot play well under its resonant frequency. In our example, we have a speaker which has a resonant frequency off 92 hurts. We can tell that by the impedance shared, the spiking impedance corresponds to the resonant frequency of the driver. This means that this driver will not play well under 92 hurts because it's below the resonant frequency of the driver. However, it will not have any difficulties playing 100 herds 150 hertz and anything above 92 hertz and especially 92 hertz, which is it's resonant frequency.
13. 5.2 Qms Qes and Qts: que also called the quality factor or damping factor. It doesn't have a unit of measure, or we call it the unit Lis. The damping off a speaker is a characteristic that helps it resume its rest. Eight. As the speaker starts to move the damping off the speaker ensures that the cone goes back to 0.0 in a controlled fashion. So we can see in this grab the cone excursion, which is high in the beginning, and because of the damping off the speaker, it slowly starts to go back toe. It's resting position, so we have less going movement and less and less until it settles down. Without adequate damping. A speaker would move uncontrollably at resonant frequency. Que actually stands for quality factor and is the inverse of damping. As damping goes up, the cue number goes down, but it's widely accepted that cues a measurement of damping. So if we compare, let's say, a speaker with a cue off 0.5 in a speaker with Q off one, the 1st 1 has more damping. Speaker damping is off two types. Mechanical and electrical. The 1st 1 Q m s, also called mechanical que is the damping made by the suspension of the driver, the surround and the spider of the speaker. Now this is fairly obvious and doesn't need much explain. The suspension has a considerable contribution in ensuring that the speaker has a smooth motion. Curious, also called electrical Q is the damping made by the coil magnet assembly. Now this requires quite a detailed explanation, and I don't think it's really necessary to complicate things but to keep it short when the coil moves through the magnetic field. Since it's an in DR it has a property called inductive, it's it will generate the current, which opposes this motion called back E M F. So when the coil is moving upward, it creates an electrical force that pulls it back. Hence, the electrical damping que two years, also called total Q, is the damping made by Q. M s and curious Combined, they don't literally add up. Instead, used this Formula one over Koteas equals one over Q m s plus one over que es. It's like adding resistance is in peril. Or, to be more specific, you can use this formula, which is the produce off kms and curious over the some off Q. M s and curious
14. 5.3 Cms and Vas: CMS is the compliance of the speaker and is measured in meters per newton. The suspicion of the speaker this around in the spider has a certain stiffness. If the suspension is thief, the driver is not compliant, so the easier it is to move the speaker, the more compliant it is. Ah higher CMS will yield a lower FS or resonant frequency. Compliance is in direct correlation with the resonant frequency. If CMS goes up, efforts goes down. Imagine a ball on the spring. The stiffness of the spring determines the compliance. We will see later that that ball is actually the moving mass or MMD. But don't worry about that too much. Just focus on the spring. If the spring is loose, when you pull and let go off the ball, it will make long and slow bounces, therefore less cycles per second. So lower frequency and the other way around. If the spring is stiff, imagine a car spring. You can barely bend it. When you tried to flex and release it, it will make very fast, short bounces invisible to the eye, hence the higher frequency. In conclusion, higher compliance or loose suspension will yield the lower resonant frequency and lower compliance or stiffer suspension will yield a higher, resonant frequency. Now let's talk about V s or equivalent compliance. The year inside the Cabinet has its own compliance. When you try to compress the air inside the box, you will encounter resistance. If the box is small, the air is hardly compressing, therefore less compliant. And if the box is larger, the air is easier to compress. Therefore, more compliant. Ves describes the volume of the year inside the cabinet where the compliance of the speaker matches the compliance of the year inside the box. So V S is basically CMS expressed in leaders or cubic feet or some other unit of volume.
15. 5.4 Re and Impedance: R E is the D C resistance, and it's measured in homes not to be confused with the impedance off the driver. The driver impedance depends on frequency anyway. This year, resistance is like taking the voice cool off speaker and pretend it's a resistor measure. How many homes it got. And there you have it. That's Ari are you will have a lower value than the nominal impedance off the driver. If we take a spec sheet off a random driver, we can see that the nominal impedance in this case is a domes. Expect Ari Toby between 10 and 30% lower than that value in this case, 6.6 homes. If the driver would have bean forums nominally, Beaton's are, you would have been somewhere between 2.6 and 3.6 homes. Impedance is the A C resistance. This is not a fixed value because the speaker is moving. The impedance varies with frequency. Let's look at a typical impedance chart. Usually the manufacturer were called one number like forums or a Tums. But that is just to make things simple, and it's called nominal impedance. Let's analyze the chart. If you haven't noticed already. This is an eight on driver, while the impedance varies from six homes toe 30 plus homes. The eight on value is considered to be the mean value at around 110 hurts the impedance spikes, and this indicates the resonant frequency of the driver at resonant frequency. The speaker will pose a challenge for the amplifier because of the increased electrical impedance. However, add resonance. The speaker is moving with the least amount of effort physically, so things actually balance each other up. Also, if we go up in the frequency range, the impedance will increase as a result. This happens because of the inductions off the voice coil. Ah coil will progressively impede the current flow as frequency increases. That's why coils are used. Impassive crossovers toe filled their high frequencies from woofers. Since the motor system off speaker contains an actual coil, you get where this effect comes from.
16. 5.5 Xmax, Xmech and Sd: X max is the maximum distance the cone can travel without distorting and is measured in millimeters. The coil has a certain length and moves up and down inside the magnetic get off the motor. So in our little sketch over here we have the pole piece in the front blade and in between them we have the magnetic gap. And of course, the voice coil travels up and down inside this gap. In this picture we have. Right now, the speaker is resting and the voice girl is placed in the middle relative to the gap. If the voice girl travels too far and leaves the magnetic gap, the speaker will distort as the magnet has reduced control over the voice coil to give you another example here, X max is reached but not exceeded as the coil is still inside. The magnetic gap exceeding ex Mex, although not recommended, will not damage the speaker. If it's done on the short time, it will only introduce distortion. It is widely accepted that exceeding ex Mex by 15% will not introduce audible distortion. Ex Mac is the maximum distance a speaker can travel without damaging the driver. When a driver is exceeding. The quoted X max distortion is introduced into the sound. If a driver exceeds the quoted X, make, the mechanical limits of the driver are reached and damage can accord to the speaker. When the speaker travel forwards and reaching the X Mac, it will stretch this around until it can't move forward. It looks and sounds disturbing. On the way back, the voice coil will hit the back played off the magnet, and we'll some like loud bangs and knocks don't exceed X make of the speaker because it can damage it is thes the effective very off the court. To calculate this, you have to measure the diameter of the speaker first. And if you're measuring an eight inch speaker, for example, the diameter is not eight inches. It will be slightly less than that, and that is applicable toe old speaker sizes. The effective diameter is from the middle of the surround to the middle of the surround on the opposite side. Knowing the diameter, you can calculate the area by using those Circle area formula, which is pi times radius squared. This means that speakers with larger surrounds will have less effective cone area because half of this around is not taken into consideration. The surface area of the cone, together with X max, is going to directly affect how much sound pressure that will for will generate.
17. 5.6 Mmd and Mms: Now let's talk about them. MDNM m s, which is the moving mass measured in grams. If you place on a scale all the components which are moving So the cone, the coil half of this around and half of the spider You got yourself the value off MMD, which is the moving mass. If you add to this equation the weight off the air in front of the speaker, then you will give the M. M s value when the speaker is moving the pocket of where directly in front of it will move in synch with the cone. This air has its own mass and has to be accounted for when calculating the total moving mess. So the total moving mass or an M s is MMD plus the weight of the air in front of the comb. The moving mass directly influences the reason frequency of the driver. Remember the bowl and spring analogy. While the compliance represents the spring, the moving mass represents the bowl. If the ball is heavy, it will force the spring toe, make long bounces, so less cycles per second, therefore lower resonant frequency. Imagine the car spring, which is very stiff and forces. Ah, hi, resonant frequency. Now I'm going to exaggerate a bit. But let's say I attach a two ton Balto the spring. It will definitely flex it easily, even though the spring is stiff and forcing the resonant frequency to go down. In conclusion, hi MMD will result in tow. Lo risen and frequency and lo mmd will result in a higher, resonant frequency. Now this concludes our feel small parameters park. Now I want you to know that there are other parameters that I didn't talk about, like l e or inducted since BL or force factor etcetera. I just wanted to keep things simple and cover the ones which are relevant to our course.
18. 6 Decibel scale: before we move onto enclosure types, I want to talk a bit about the decibel scale. First thing to know about it is there is not linear. It's logarithmic. What do I mean by that? If, for example, one sound is measured that 50 decibels and another is measured that 100 decibels, you would be tempted to say that the second sound is twice as loud, and you would be wrong. In fact, you would be way off on a logarithmic scale. It's not that simple. Let's look at an exponential scale because it's more familiar. If you look at it, how it progresses, you can see that it has a hard time at the beginning, increasing slowly. But as it continues to develop, the value increases well, exponentially. After a certain point, it shoots up. The logarithmic skill is exactly the opposite. At the beginning, it progresses very fast, but then it gets immensely more difficult to increase in value. Let's put things into perspective. Let's say, put a decibel meter at one meter away from my head. I can easily reach 100 decibels just by raising my voice, but it would be impossible to reach 140 days a bus, no matter how hard I shouted. Scream decibels are used measured voltage power and acoustical pressure and they have different connotations. D B, u d B v d b w db spl, d, b p w l and many more. All these units of measurement are not our focus right now because they are not relevant to our course. Except for one. We are interested in DB SPL, which measures the sound pressure you can find. This value in the specs kicked off the speaker as officious. Your SPL quoted usually it one what, one meter or, at 2.83 votes, one meter? Here are some examples Efficiency of Speaker X quoted at one what one meter is 90 decibels in the efficiency of speaker? Why quoted that 2.83 volts? One meter is also 90 decibels. Please be careful about this reading within quoted the 2.83 volts. Then you have to take the nominal impedance Ito account. One. What is one? What, regardless of the impedance, But when using toe pointed rewards, it will have different power ratings, depending on the impedance off the driver, for example, If Speaker Wise rated that 90 disciples at 2.83 volts, one meter and has a nominal impedance off four homes, then the efficiency of one. What one meter is three db less? Because 2.83 votes in tow forums is actually two watts. Not one. What so efficiencies. Actually, 87 decibels. It's one, what, One meter. But let me give you a practical example so you can understand how to comfort to 0.83 volts . Toe one. What one meter? Let's say the speaker is rate that 85. Suppose had two pointed it revolts one meter. If the impedance is eight homes, then the rating is 85 decibels at one. What, one meter? If the impedance is four homes, then the rating is a to do disciples. If the impedance is to homes than the rating is 79 decibels at one what, one meter and so on. If the impedance of the driver is a tomes, the ratings match. Regardless of the ways measure, usually the speaker manufacturer will use the 2.83 volts waiting to make efficiency look bigger for low impedance drivers. Don't not get fooled by this. If you want to get an idea on how loud your speaker will get, you can make a rough estimate by knowing the efficiency at one. What, one meter in the rated power of the speaker. This is considering that your amplifier has leased that amount of power. So if you look at this spec sheet from before the speaker, efficiency is 86.1 decibels at 2.8 if revolts. But since it's a NATO driver, it will have to same efficiency at one. What, one meter? If we feed the driver two watts, we get an additional three decibels. So 89.1 decibels. If we feed the driver for what we get an additional three decibels. So 92.1 it eight watts. We get 95.1 and every doubling off the input power yields an additional three decibels. We can do this all the way up to 50 watts, or we can use this formula. The formula for the maximum SPL is equal to the efficiency. It one what, one meter plus 10 times the luxury off the max power. So in this case, the Maxus Beal is 86.1 plus 10 times log off 50. So let me bring the calculator for just a moment so I can show the calculations. We got 50 longer if times 10 plus the efficiency at one what one meter, which is 86.1, which is equal to 103 decibels. This is a rough estimate. It doesn't include the effects of the enclosure or the reflections from the surroundings, but you conform an idea when comparing two drivers. Now, here are a few things to remember. Doubling the power increases this bill by three decibels. Increasing the power by 10 times increases the SPL by 10 decibels. This is actually a fortunate coincidence on how longer it's work. So if you've got one what that 90 decibels At two watts, you will have 90 free at 4 96 at eight 99. At 16 you will have 102 and in between it 10 watts, you will have 100 decibels so you can see from one what, 10 watts, which is 10 times the power. We got a 10 decibels increase from 90 to 100. This is fine when talking about power. But what about perceived loudness? It is considered that three decibels in sound variation is not particularly detected by an untrained year, and 10 decibels is considered to be twice as loud. So 20 decibels would be four times as loud. 30 decibels difference would be eight times as loud. Again, we're talking about perceived loudness from a subjective standpoint.
19. 7.1 Enclosure types: There are many types of enclosures out there, but we're gonna talk about only the main ones. So we're gonna talk about the even the baffle, the sealed enclosure or closed enclosure. The base reflects a reported band pass enclosures and transmission line enclosures. Before we take each one apart, let me explain what is the purpose of an enclosure like we established in the chapter about phase the speaker produces sound in front of the cone and in the back of the comb. Problem is this. Front waves and back waves are exactly 180 degrees out of face, and they cancel each other up low frequency responses that really affected by this issue. Therefore, the main purpose of an enclosure is to separate the front waves from the back waves.
20. 7.2 Infinite Baffle: Let's begin by talking about the infinite baffle. The infinite baffle is something a bit your topic sounding because it refers to a baffle that extends indefinitely into all directions, therefore completely separating the front waves from the back waves. What about the final Bethel, considering that the wavelength off 20 her thes 17 meters if you have a baffle which is 17 meters across with the speaker in the middle, you effectively got on infinite baffle Onley. 19 hertz and Lower will have long enough web links to travel around the baffle to achieve cancellation. But we can only hear down to 20 hertz, so that's a nice compromise. Anyway, a 17 meter board seems a bit of a stretch. Also, does this type of an enclosure even exist in the real world? Well, it does actually, but in different forms which become being too most of the time. Benefit baffle is called a very large sealed box. Since the boxes large with volume bigger than the speaker of us, the air inside the box doesn't help them put the speaker in. It only acts like a barrier to separate the front waves from the back waves. Ah, good example, often infinite baffle enclosure is in a car when you place the speaker in the rear parcel shelf with the magnets sticking inside the trunk, the front is radiating sound inside the cabin, and the rear is radiating sound inside the trunk. The waves are completely separated in the trunk. X like the oversized sealed box. No, let's see, What are the pros and cons? The pros. It doesn't need much power. Usually it has less distortion compared to other enclosures and in an ideal infinite baffle set up, which is actually a finite baffle but sufficiently large enough, there are no resonances and no diffraction issues, and the cons the wolf for can reach maximum excursion easily, so you need to be aware not to damage.
21. 7.3 Sealed: the sealed enclosure. We're gonna talk more about this type of an enclosure when we'll discuss designing it. But first, let's cover the basics. A sealed enclosure is exactly as it sounds like. Places speaker in a perfectly sealed box, and there you have it sealed enclosure. However, the volume needs to be something smaller than the speaker of yes, so the year inside the box acts like a spring and helps them the speaker. Otherwise, it would be an infinite barefoot and again. Since the back waves are trapped inside the enclosure, they do not meet with the front waves to achieve cancellation. The pros for the sealed enclosure. If space is an issue is sealed. Enclosures are the smallest. They are easy to design, easy to build. Design errors don't have much impact on the overall sound. They have great transient response. This means they play with little effort to short durations, sudden sounds like drums, and it has a smooth roll off off 20 decibels. Productive. As for the cons, it has very low efficiency, and therefore it's not the loudest enclosure design
22. 7.4 Bass Reflex: Now let's talk about the bass reflex based reflects is the meat and potatoes. When it comes to speaker enclosures, it's one of the most common enclosures out there. Why? Because it offers a great balance between quality, efficiency, design and build difficulty. Again, I will go more in detail about this enclosure when we are going to learn about how to design one. But the bottom line is that the base reflects enclosure is basically a sealed box with a pork usually cylindrical, the mass of a recite. The port resonates with the compliance of the year inside the box. Therefore, creating an additional speaker on limited frequency band with this is depending on the tuning frequency of the box. But more details about this in the section dedicated toe base reflects design. No, let's talk about the pros. Incomes, the pros, higher efficiency than sealed. On paper. It's about three decibels. The speaker can reach lower frequencies outside of its frequency response. Reduced distortion. The speaker doesn't need to move us far near the tuning frequency off the box, and because of this, you can feed more power to the speaker. So higher power handling the cons. It doesn't have his good transit response as the sealed enclosure. It is more difficult to design and build compared to sealed based reflect. Sport can become noisy at high volumes. It is larger than sealed, and it has a steep roll off 24 decibels prerogative.
23. 7.5 Bandpass: Now let's talk about the band pass enclosure. There are a few types of enclosures when it comes to Band Pass 44 there's sixth and eighth order band pass. The speaker is out of sight inside the Cabinet, and the sound comes only through the port or ports for the fourth or their band pass. One side of the speaker is placed in a sealed enclosure while the other side is placed in a ported enclosure. In this type of design, the wool for plays louder than based reflects but has a narrower frequency response. You can make the wolf or player broader frequency response, but that is that the expense off efficiency sixth order Band Pass has both chambers sported , while eight order Band Pass has an additional ported chamber. Now let's talk about the pros and cons. The pros. It has high efficiency, a theoretical plus five db compared to sealed lower wool for excursion. In a good choice for high SPL applications, the cons enclosure can get in practically big, extremely difficult to design, with no room for error, especially for the sixth and eighth order if June for efficiency. The sound quality is very poor, it will sound loud, but it will have a very narrow frequency response band with if pushed the limit, you will not hear the wolf are struggling as it is inside the Cabinet and you might damage it unknowingly.
24. 7.6 Transmission line: No, let's talk about the transmission line. This is a unique enclosure type which is quite difficult to pull off. The basic principle is this. You make a path from the back of the speaker to the front, which is exactly in length, equal to 1/4 off the wavelength off the resonant frequency of the driver. Now what I mean by that let me give you example so it can understand more clearly if the driver has a resident frequency off 50 hertz, for example, the wavelength or 50 hertz is 343 divided by 50 which equals 6.86 meters. To find out the quarter wavelength, we need to divide that by four, so 1.71 meters. So basically we make a path from the back of the speaker to the front, which is equal to 1.71 meters long. This is usually done by making elaborate, so you are space efficient. By doing this, you will delay the resonant frequency back wave by 1/4 cycle. These means the sound will come out 90 degrees out of phase relative to the speaker, and it will reinforce the front waves. By some degree, however, these poses some problems with the rest of the frequency spectrum. You will need to apply sound dumping material along the line off different thicknesses and densities to absorb all the upper frequencies. What are the pros and cons? The pros? You will have, Ah, great low frequency response. It can reach subsonic frequencies, and it's not so sensitive to positioning the coms. Because of the extra elements inside the Cabinet, it's more difficult to produce. It's hard to design it because the upper frequencies are very unpredictable. The box can get very large and size, and there were four moves. More or less freely. Anything can reach maximum excursion easily.
25. 7.7 Hoffman's Iron Law: a few moments ago, I said something like, Based reflexes really be louder than sealed or bad. Pass has a narrow frequency response band with compared Toa base reflects these air some general guidelines. In reality, Hoffman's Iran law is in effect, which states between enclosure size, efficiency and low end extension. You can only choose to try not to view it that bluntly. Imagine three sliders, each representing box size, the other efficiency and the other one the low end extension. If you move one up, you have to move one of the remaining two down by the same amount, or you move both down by half of the amount you'll get the general idea. So, for example, if you want an enclosure that is small and plays very low, expect for you to be very inefficient. As in, you will need to feed it a lot of power. Or if you want an enclosure that plays very low and it's efficient, expect for the box to be very big
26. 8.1 Sealed enclosure: it's unfinished with explaining all the introductory terms, we cannot finally focus on how to design a speaker enclosure, and I shall begin with the sealed enclosure. This type of an enclosure has many names sealed, closed acoustic suspension, air suspension. The air suspension name comes from one of the defining properties of the sealed enclosure. The fact that the air inside the box helps them the speaker. This air spring will alter the overall total cube over the system. If the box is small, the air spring is differ. As the box gets larger, the air spring effectiveness diminishes. Increasing the volume of the box by too much will slowly negate the effect of this spring, and the enclosure will transform into an infinite baffle. The overall que of the system. The box plus speaker combo is called Q T C, and this is the number you will need when designing a steel box. Now I'm not going to bore you with mathematics and show you how to calculate Q T. C. Because we have the Excel spreadsheet for that which I will show you later on. But for now, I'm gonna tell you the basic guidelines. Q t s is equal to Q M s plus Q. Yes, Now we know they don't literally add up, but this is just to make a point. And q t c is the cue of the box plus Q t s. Now we can see what the different letters stand for. So mm means mechanical e electrical s stands for speaker T for total and see for the closed box. So if you look at the Q. M s is the Mechanical Cube, the speaker Q T s is the total q of the speaker. Q. T sees the total Q of the closed box and so on. Now when we designed the box, we aim for different values of q T C, depending on our application and what our goals are. Different values off Q t c will result in different sound signatures. Let's start with the QD C off 0.5. Here is the model frequency response. This alignment has a very good low end extension and the best transit response we call transients. Those sudden sounds like drums when the speaker plays a sound and then immediately miss to play another sound. This means that the speaker has to recover quickly from the first town to be able to play the 2nd 1 If the speaker is slow to respond or it has a bad transit response, the sound will be muffled. This Q T c off 0.5 will help the speaker have a great transit response. Problem is, is not the best when it comes to sheer output volume. This alignment is also called liquids Riley, or because of the low value off Q t C. It is also called over that Now let's move to a higher value of Q T C 0.7 or seven. This is the number most people try to reach for as it gives good transients. Ah, flat response and minimal cut off. This is also called the Butterworth Alignment, and it gives a maximally flat response now acutely see value between 0.7 and 1.2. It is called a chip chip, uh, response. It has, ah, better efficiency, somewhat degraded transients and a steeper roll off. The response is not linear anymore and has a peak in response, larger or smaller, depending on the value of Q t C. Some simple for manufacturers will choose this type of response with Acute GC between 0.8 and 0.9, because it yields a slightly smaller box with the more punch sound but all of the expense of linearity, an acute GC off 1.2 and above. This is also called the Chip Shop Response. In fact, anything above 0.7 is a chip response because it's not a linear anymore. Anything about 0.7 will have a peak in the response. Here is the model frequency response. Anything with a qd c above 1.2 will have a high efficiency, bad transit and bad to frequency response. This type of response is also called under death. This is a no go regardless of the application, as q T C increases too much. Although the box gets progressively smaller, the Peking frequency response gets bigger and bigger toe a point where it will sound like one note sub before the Peking response is so large that the response is disastrous. We are probably looking at the response in saying the responses linear till the resonant frequency point, and then I get a picking the response so those frequencies will be louder. So actually, it's a win win. I get a linear response, and then additional base near there isn't efficacy. And the small box problem is that any frequency, which is three db or louder than the rest of the frequency, is too loud compared to them, and they will be covered up. It's like when you're in a noisy room and then blast your headphones full volume. You don't hear the room noise anymore because the head forms are too loud compared to the room volume. This means that this sub will play on Lee this section off the frequency response bandwidth because the rest is covered by the loudness of this section of the response. That's why it's called a one notes up because it literally plays one note, which is the resonant frequency. The conclusion is that when you're trying to design a steel box, you are trying to reach a certain Q T C number. You can go for a big box in a Q T C of 0.5 to have the best transit response. Most of the time, you will want to aim for Q T C 0.7 or seven to have the best blend off box size, transit response and very good frequency response. Q T C. Between 0.8 and 0.9 for a slightly smaller box. Higher efficiency. But for the small peak in the frequencies bus never go for a box with Q TCO 1.2 in higher. Now let's fire up the Excel spreadsheet and start designing.
27. 8.2 Sealed enclosure design using the excel spreadsheet: first, let me give a short briefing on how this works. If you see an orange cell, it means you have to input the value there. A grey sale will indicate that there is a formula behind it, and an automatic calculation will occur there. Now the spreadsheet is protected, but it isn't password protected. The only purpose for the protection is that you don't miss up the cell with the formulas. You only shouldn't put values into the orange sells. So if you input, the value here is fine. But if you try to him with a very here, you'll get them ever message. You could remove these protection by doing this, but then you might mess up the formulas, so I suggest you leave it on now at the bottom. In the worksheet area, we have five different worksheets we have sealed, which we will discuss. Right now we have based reflects, which will discuss later on the base reflects the lineman's again, not of your concern, right, for right now and then I have ah, two additional tabs, which are the scene with the first to seal them based reflects, but they use the imperial units of measurement. So instead of leaders, you have ah cubic feet and East Ed off millimeters. You have inches for the rest of this tutorial. I'm going to use the metric system. So let's try and design a sealed enclosure for a particular driver. Now on top, you will see that we need to input three speaker parameters. The big three we talk about in the TS parameters section the resonant frequency, the Q T s and the V s or equivalent compliance for designing a sealed enclosure. I selected a 12 inch sub before to serve as an example to what I'm about to show you. So go ahead and copy the three parameters from the spec sheet off the driver we have. The FS, which is 22.2 hurts Q t is is 0.45. NVs is 97.2 litres. If we move downward a bit, you can observe the box parameters section. The only variable in the sealed box is the volume, That's it, and you will have to input it yourself. Depending on the volume you choose. The rest of the parameters are calculated automatically. Que el refers to the box losses and simply ignore it. This is relevant when we will get to the base, reflects enclosure in a shielding pressure, usually stuff it with sound dampening material and induce a lot of losses anyway. But nevertheless, just pretended Que el isn't even there? FB is the resonant frequency of the box, which will always be something higher than the resident producer of the driver. Since we are placing the speaker in tow a box, the air inside the box has a certain compliance. Therefore, it will make the speaker more stiff. Remember the car spring analogy Stiffer spring or lower? Compliance means higher frequency. F three is the point off three db below linear response and Q T C is the total Q off the box plus speaker system. It is calculated automatically, depending on the volume you choose. If we move further down, we can see a Q T C calculator. So if you want to reach a certain Q t c, enter that value and the calculator will tell you the exact volume the box needs to be. So let's say we want a box with a Butterworth response. Simply enter 0.7 or seven in the Q T C calculator section, and then it will return the volume off the box. Then you can go up and enter the volume in the V B section 66.19. After that, all the parameters are calculated and the modelled frequency response is also shown. If we want to make the box smaller, Q T C will go up and the response will start to peek as we are entering the chip Ishiba alignment. So let's see. We want to make the box 40 leaders. The Q T C has gone up to 0.83 and you can see this light peak in the response. If we go even lower 20 liters, we can see the q t C has gone up even further toe one point 09 and the peak is about to disobey rules. So let's go even lower. At 10 liters, the Q T C is almost 1.5, and you can clearly see from the response that this is not usable as the linearity is severely affected. If we go to the extreme, let's see one liter. I'm not sure if that is even possible, but just to make a point. The Q T C is almost 4.5, and you can observe that it results in a monstrous response on the other end of the spectrum. If we keep increasing the volume, the Q T C will progressively go down. So let's see solid If we go toe 200 liters, the Q T C is now 0.55 500 leaders 0.49. And let's make the box of ridiculous size, Let's say 10,000 liters. You can see now that the Q T C is basically the same with the Q. T s of the speaker. This means that the box doesn't affect the compliance of the speaker. It is so big that is basically a new infinite baffle. What we are calculating here is the Net internal volume of the box. These means that you have to add the volume displaced by the speaker and any other bracing you will place inside the box. The volume displaced by the speaker is usually quoted by the manufacturer. If not, you can make an approximate guess. Now let's move on to the paid application
28. 8.3 Sealed enclosure design using the paid application: I chose Subbu for Design Toolbox. There are just a couple of reasons behind this decision. It's the cheapest, and it's the simplest, and that's it. I'm not an affiliate of any sort with the guy that makes this software is just my recommendation. If you're a beginner and if you are taking this course, you probably are. If the software is simple, you will understand it better. When you fully comprehend this entry level software, you can step it up. You might disagree with me and probably thinking like I'm going to buy a fancy a closure designed software. It might be more expensive and difficult to understand, but I will eventually get it. I strongly disagree with this. Let me give you an example. I present to you sound easy, and this is a pretty top notch software. When you open the app, you are greeted with this screen, and you can see how much complexities we are probably familiar with the TS parameters in this section. But if you move through the enclosure design, you can see all these dabs over here that some of them you don't even know what they mean, and then when you move on to the actual designing, you will probably get overwhelmed and abandon it. That's why it is better to start light and progressively move upward in difficulty. That is my recommendation. So let's move back to our simple software. First of all, let me show you where you can get from simply go to Google and types of before design toolbox, and it should be the first result in Google, or you can access directly the website MFR High Fun E N g that com slash toolbox dot HTM. Then you are greeted with this shady 19 nineties looking me html website. But trust me, it's legit. Go to order section and after you purchase it, you can immediately down with it. Now, when you open the app, you are greeted with four types. First is where you will design the enclosure. Whether it's sealed or based reflects the second dab is where you will design the port of the base triplex enclosure. This will be our focus in the next part of the course. The third tab is where you physically designed the box. After you have calculated the volume and the fourth tab here you will be given some recommendations about your particular driver. So if we entered the driver parameters, we have the FS point. French 2.2 Q t is 0.45 NVs 90 Say, what's going to use me? 97.2 litres. So we have a figure of merit. This basically is like a mark the speaker gets depending on how good it is, how deep it goes for the volume it demands. Something close to 100 will be a more desirable speaker. But don't get too hung up on this. I completely ignore it. Then the estimated freer response is also something that is not a particular interest now. Below that, you will get some recommendations. It says that the speaker is better off in a sealed enclosure, which I totally agree and only go for based. Reflexively enclosure is bigger than 40 liters. You can also see different frequency responses for different box volumes. Now let's move back to the enclosure design and let's first enter the parameters again point to to 0.45. Switch the leaders 97.2. No, this is pretty much similar to the Excel spreadsheet. We choose how many drivers are inside the box, so if they are to, you're going to select two. But there is only one, so we will leave it on changed. Then you can choose the enclosure type, which can be sealed or, ah, ported the which is the base reflects, and you have an additional band pass enclosure. But that is not the focus off our course. So let's choose sealed optionally. You can choose a car response. Let's say if you place the speaker in a car, the car response, we'll show you how it will affect the response, depending on the size of the car. But we are interested in, in the end, it quick response, so we'll leave it at flat or not. Now, what's different from the excess pressure is that you can overlay multiple response curves , and we shall do just that to illustrate the differences between different values off UTC. Unfortunately, these up does not have a Q T C calculator, so we are going toe head back to the spreadsheet and calculate for each of the Q T C values 0.50 point 711.2 and 2.5 and see how they stack up to each other. So let's start with the 0.5 we have. Ah, we have 414 liters, and then we're going to give it the name. Q T C equals 0.5 and click of the plot. And then you should unsealed the response in the in the chart. Then we're gonna hit new data set and see the volume for 0.77 UTC. And we have, ah, 66.19 liters. And we're gonna name this, uh, if UTC equal to 0.77 an update plot, then we're gonna click new data set again. And we're going toe four q t zero value one. So we have the volume one for 24.68. We're going to rename it toe Cutchogue photo one. Probably plot new data set, and now we shall go for 1.2 UTC. We have ah, 15 0.91 liters. Let's rename this would you see equal to of the plot? New data set. And now we're going to go for 2.5. And there we have 3.25 liters, then renamed the data set to do T C equals five and update plot. Now let's switch this the full screen so we can, uh, discuss the different values. Now you can see that the lower the Q T C is the lower in frequency. It will go. So if you follow the red line, which is the Q T C 0.5, you can see that from this point forward, it has a better lower frequency response. Now, if you follow the Butterworth response, which is the green Line, you can see that it gives a maximally flat response. And from this point forward for ah Q T C off 11.2 and 2.5. The response starts toe peak as que TC goes up, it will peak even more, and the low frequency response is also affected. As you can see, the response curves are moving to the right and also for high numbers off q T c. So 2.5 the peak in response is ridiculous, so this is clearly not usable. Now let's exit this foot screen and trying to design the box. Let's say we go for ah Q T C off 0.7 or seven. So we have Ah, 66.19 liter box. We can go to the enclosure designed tab, and we know the volume is 66.19 and we can choose the the shape of the box, which can be rectangular or a witch, which is a trapezoidal shape. But we will go for ah, more conservative rectangular shape. Let's use the wall thickness. Very minded. Desire the outside dimensions so the thickness of the wall is relevant. We're gonna go for Ah, 19 millimeter thickness, which is 3/4 of an inch, and this is a standard I mentioned when it comes to MDF or plywood boards. Now, to calculate the dimensions of the box, we need to enter manually two dimensions and then the program calculates automatically the 3rd 1 So let's say we go for 340 millimeters by 450 millimeters, and then we can calculate the third dimension, which will be 570 millimeters. Now let's imagine that the 570 millimeters we just calculated is too large for where I'm going to place the sub before, So let's see the maximum there. Mention here is 500 but I can spare more space into this dimension, so I'm going to complete this one. So now we have 385 millimeters into this side of the enclosure. Now, after we are satisfied with the overall outside dimension of the box, you can click short template, and you will see an exploded view off all the boards that make up the enclosure. This makes it much easier to calculate the box, and it's easier to see what's what when actually building the enclosure.
29. 8.4 Stuffing: it is common practice to stop the box with absorbing material, you can line the walls with it, or you can literally fill it up. Many materials can be used polyurethane, fibreglass, feeling bonded cellulose, acetate, fiber, long fiber, wool, etcetera. The stuffing has various advantages. Absorbing standing braves. The whole point used to separate the waves generated by the front of the speaker from the ones generated by the back. It is obvious that absorbing some of these back waves will do some good diminishes the panel residences. Placing absorbing material on the walls of the enclosure ensures low resonances. The thickness of the damping material is important if you need to absorb sound waves off certain frequencies. The back panel is the one who needs this damping the most, because back ways reflects from the back panel. Come back towards the speaker and come out through the speaker panel. Residences are minimized by using thicker enclosure walls or by using internal bracing. But the absorbent material is also very effective. Another advantage. It would be that it increases the internal volume of the box. This is a bit harder to understand, but the technical term is Aiso thermal propagation. I'm going to try to explain it more user friendly so you can understand. Because of the feeling inside the box. The sound waves will have a harder time traveling through this medium because it takes longer for the sound waves to reach the extremities off the box. It simulates the exact effect off having a bigger box. Adding stuff into your box will translate into 15 to 25% volume increase. We are talking about the effects that happen when increasing the volume, because obviously the physical box size will remain the same. Another advantage will be increased efficiency. If the damping of the box is done right, you are looking at up to 15% efficiency increase Now Here is an example of a sealed enclosure I made to see how easy it is to make one the wolf for had the following parameters. Resonant frequency off 24.9 Hertz. Total Q off 0.45 NVs off. Ah! 139 leaders. So for a Q T C off 0.7 or seven, the box volume needs to be 94.66 liters. Now we have to add the volume displaced by the magnet assembly. But I'm not going to do that because I'm going to feel the box with the loudspeaker wool. The dimension I choose for the box is, Ah, 592 by 420 by 470 millimeters, using 18 millimeters thick boards. This resulted in 92.77 leaders, which is lower than I need even lower, considering that I have in this place the volume of the magnet. Let's see what happens when I feel the box with dampening material. Now I have the necessary means toe measure. This changes So after I feel the box, the resonant frequency has changed, as if the box had 101.21 leaders. So I gained about 10 litres, which is roughly 10%. But wait, I aim for 94.66. Laters. What does that mean? If we currently the Q t C. For the new volume, we can see that the Q T C is 0.69 which is more or less the same with Q t. C. Off 0.7. This is a nice part about designing a sealed box. You can be 5 to 10% off and you're still on the right track. That's why the sealed enclosure is recommended for beginners.
30. 9.1 Bass reflex enclosure: Finally, it's time to discuss the base reflects enclosure. Now this is the most popular enclosure out there, and for good reasons it gives better efficiency for the amount of volume demands. And for a little extra cost. It has reduced distortion, better power handling, and it can reach frequencies below the resonant frequency off the driver. Now, I already mentioned these perks before. The difference is that now, as I dig deeper into the design, you'll understand why. First of all, let's see how the design functions. It's basically the same as the sealed enclosure, but with the added vent or port, there are a lot of misconceptions on how the sport actually works. Many think that the back of the speaker compresses the air inside the box and then pushes it out the vent. While this might be uneducated observation, it couldn't be further from the truth. On one hand, we already established at the beginning of the course that the air molecules don't move. They vibrate and set the air particles next to them to follow the vibrating motion. On the other hand, if this were true, the sound waves generated by the back of the speaker will come out through the port to meet with the front waves and cancel each other out. You're probably confused in the asking yourself. How come this doesn't happen? Well, this would be true if there were a whole in the box, but it's not the whole it's a pipe in it X Like a resonator, the air inside the tube has a certain mess and resonance with the compliance of the air inside the box. If you want to make the ball in spring analogy, the ball is the mass over there inside the pipe, and the spring is the air inside the box at certain frequencies. The year inside, the port vibrates violently and acts like a second speaker. The waves generated by the vibrating mass or they're inside the board. Add with the waves from the front of the cone. The port has a certain resonance frequency, and that is the point where it gives the most output. So let's look at the port frequency response. We got frequency on the X axis and magnitude on the Y axis, and we can tell that this sport is June that 60 hertz, as it's the point of maximum output. As we move away from this point, the effectiveness of the poor diminishes. So if you go down in frequency, let's say 50 hertz or 40 or 30 hurts. You can see that the magnitude is lower and lower on the other side. If we move up in frequency 70 80 90 or 100 hertz, we also lose amplitude. In conclusion, as we move away from the tuning frequency of the port, we progressively lose amplitude 22 in the port to a certain frequency, you have to take into account three factors. The internal volume of the box, the diameter of the port and the length of the port. Altering any of this free will modify the tuning frequency. Understand that the resonant frequency of the box is independent of the speaker. You place in it so you for boxes tuned to 40 herds, it will be June 2 40 hertz. Regardless of the speaker to place inside it, different speakers will have different frequency responses, depending on the parameters of the speaker in the size of the box. But when we are talking strictly about the tuning figures of the box, the dimensions of the box in port are the only things that matter. It's interesting to know how the sport act. Two different frequencies. Let's say the Portis tune toe 50 hertz when the speaker is being higher frequencies. The massive very side. The port is too great to respond to the speaker movement, so it virtually simulates a perfectly sealed box at frequency in the close vicinity off 50 hertz. The port resonates and creates additional sound waves to combine with the front waves of the speaker and below 50 hertz. The waves pass through unrestricted and achieve cancellation with the front waves. That's why the base reflects. Enclosure has such a steep roll off off 20 for this bus prerogative after the resonant frequency has been reached back with cancellations starts to set in and the frequency response loses amplitude quickly again. These are some basic and rough guidelines, so we conform a general picture. In reality, it's a much more complex process. Now let's move won't report saying the most common used ships for a base reflect sport is either cylindrical or rectangular, but virtually any shape can be used. Rectangular ports are made using pieces of material you are using to make the box, usually MDF or plywood, but most often circular ports are used. These are made by various materials, mainly plastic. But if your local audio stories out of basically exports, you can successfully use a PVC pipe. For example, for the ongoing discussion about these events, we're going to focus on the cylindrical one as it is more popular. We know that these four factors are interconnected, joining frequency off the box or f B box volume, or VB, poured the A meter and board length. If you change one, the value off at least another parameter will change. Also, let's consider we have a box toe fixed volume, and we want to achieve a certain FB or tuning frequency these means who have toe, choose a certain diameter for the port and then calculate its length. There are a few guidelines when actually picking the diameter of the port, the diameter of the port needs to have a minimum value. When the frequency reaches the resonance value, or FB, the port radiates almost all of the acoustical power. The speaker moves very little, and the port does most of the work, and because of this, the vent needs to have a minimum volume displacement in order to prevent power Compression . Also, a bigger diameter ensures that there will be little air movement, noise or shuffling. If the port is small, the air movement inside the port can make unwanted noise, and sometimes it can even whistle. Here are some general rules when it comes to picking poor dimensions. A one inch event is suitable for a four inch speaker or smaller. A two inch event can be used with a four inch speaker or a five inch speaker, but no bigger than six inches. A three inch event is suitable for a six inch speaker, but don't use a speaker larger than eight inches. Ah, four inch event is suitable for an 18 speaker or attain inch one, but don't go any higher than 12 inches, and a six inch event is suitable for a 12 or a 15 inch speaker. Having a flare port will increase the port linearity, reduced distortion and minimize air noise so you can get away with a smaller port sees the air is moving back and forth. Having a flare at both ends is highly recommended, not just a one end for best results. Use a port as large as possible. We will see in a minute white. There are limitations on how big you can go when choosing the port diameter. Let's give a practical example. Imagine we have a 12 inch wafer and the box volume is 50 liters and you want to tune it it 25 hearts. All that's left to do is to set a poor diameter and calculate its length. In an ideal case, the poor diameter is the same size as the speaker diameter, but that is always not the case. As you make the port larger, you need to make it longer to keep the same tuning frequency. So in our case, if I choose ah diameter for the port off five centimeters, the port needs to be 15 centimeters long. For a diameter of 7.5 centimeters, or three inches, the port needs to be 37 centimeters long for 10 centimeters. The port needs to be 68 centimeters long, and for 15 centimeters or six inches, the port needs to be 1.6 meters long. Let's take into consideration the ideal case a 12 inch wolf or will have one effective cone diameter off around 10 inches if we exclude half of this around and such so the speaker has on effective diameter off 10 inches or 25 centimeters. So if we make the port the same size of the speaker, it will demand a length off 4.5 meters. So you can understand why there are certain limitations. A length off 4.5 meters, basically silly, even for the diameter of 15 centimeters. The poor demands a ridiculous length. So the best compromise for our 12 inch wolf, or is do you support with a diameter of 10 centimeters Before we start designing a bass reflex box, I want to talk about two important things. The box losses and the base reflects the line once.
31. 9.2 Box losses: When you are building an enclosure for your speaker, it is convened that the box will have some leakage more or less, which we call box losses or Q B. When designing a base reflects enclosure, the box losses are given by three things. Air leakage or que el absorption of ah dumping material or Q A. An event losses or Q P. The total losses, or Q B, is the sum of all three, and you can calculated using this Formula one over Q B is equal to one over QL plus one over Q A plus one over Q P. If you want to play sound dumping material in a base reflects box, you don't stuff it like in a sealed box because you will obstruct the port. Instead, you will line the wall with a maximum of one inch off dampening material. Sometimes this material is absent altogether in a ported enclosure. Since the dampening material used is in a small quantities, the losses induced by this absorption is minimal. Also, considering that the port is not obstructed, Q. P is negligible is well. In this case, when we are talking about box losses, we are only referring toa air leakage. So Q B is equal to kill because the other two are negligible in conclusion, que el refers toe box losses. Que el has various values, depending on how well the enclosure is made. If Cuba has a value off seven, the box has normal losses. So use this when you are designing a box. If you're enclosure modeling, software doesn't have an option to specify que el like support for design toolbox assumed that Curiel is seven. If you will, is equal to 15 it means you have very low losses. 15 or higher, if you will, is about three. It means you have high losses, and you have a very leaky enclosure, and you should probably rebuild the enclosure or fix the issue. You cannot predict box losses, and you can only measure them after the box is finished. Also, you need some way to measure impedance, and we know that's not fixed value. It's actually a graph, so it's pretty difficulty if you don't have specialized equipment. But you cannot ignore box Lasses as they influence the overall response curve. My advice is this. Make your enclosure design using Curiel off. Seven. You should be fine. Most of the time. If you plan to use silicon sealant on every joint and seem off the enclosure used que well off. 15. Well, the box losses are unpredictable Every time I use abundant silicon sealant, I got a very air tight box when I measured que well, it was always something near 15.
32. 9.3 Bass reflex alignments: similar to the Q tissue of the sealed enclosure for based replace. We also have a line Once you can design the box, however you wish. Or you can use certain alignments, which translate into specific sound signatures, usually to choose a certain based replace alignment. Your speaker needs to have a cute ES off 0.4 or lower. There are six. Main base reflects the violence. SB before or super for order boombox a C four or $44 sub chip shift. Q B three were third order quasi Butterworth before or four for their Butterworth B E four or four for their vessel and I before or Butterworth Inter order the last. We are called discrete alignments because they exist for drivers with specific values off cuties. These are quite difficult to obtain. An we shall disregard them and only focus on the 1st 3 SB before is characterized by a large box, low tuning frequency, which means a longer event and good transit response, which, to be honest, puts the term boombox out of place. A C four has about the same enclosure sizes be before, but with different turning frequency, somewhat degraded transients When compared to SB before and Q B three is the most popular vented alignment because it yields a smaller box in the lower F Free. However, the transit response is not as good as that be before or s C four. This is similar to the equivalent off Q T C off 0.7 or seven in the sealed enclosure, which has a maximally flat response. Now, if you open the Excel spreadsheet, we have a tab off base reflects Alliance, depending on which all I want you choose. This table has all the values you need to calculate the box volume and the tuning frequency off the box. It will also show you if the response is linear or if it has a certain peak again, I'm not going to bore you with mathematics and show you how to calculate the box volume and the tuning frequency. The spreadsheet does that automatically. We will get to that when we are going to design a base reflects box. However, you can tell from this table if the response will be linear or if it will have a peak in the response. For example, let's say, have a speaker with Q T is off 0.33 and I want a Q B three alignment. So we have the SP before alignment here. The Q B three here in the S E four here. So we have to look at these cons and we're going to look at the cule off seven. So, for normal box losses, then you will search your Q t s value, which is 0.30 free. These three numbers are used to calculate the tuning frequency of the box the box volume in the free point for this specific alignment. Again, this is calculated automatically and more on that a bit later. But we can see the pig D. B in this case is zero, which means it will have a perfectly flat response.
33. 9.4 Bass reflex enclosure design using the excel spreadsheet: You should be familiar with the expression by now from the sealed enclosure, but I'm going to give you a quick run now. Enter values only in the orange sells. The gray cells contain formulas, so don't miss them up. Even if you accidentally try to modify the great sales, you will get an error message because the spreadsheet is protected now, As you can see, the base reflects, worship is a bit more cluttered. This is because the design is more complex and has an additional variable, which is the port similar to the stilled enclosure. Have three speaker parameters at the top, which you will enter manually to make the design process more familiar. I'm going to use an actual sub before here is the spec sheet of the driver. So go ahead and copy the parameters into the spreadsheet. So for the effects we have 24.2 hurts. The Q T s is 0.39. NVs is 84.1 liters. If we move further down, we can observe the books parameter section. Only difference now is that we have to enter the box losses que el manually, and we select the resonant frequency of the box ourselves. F three is calculated automatically. The bending on the values that we enter as box losses is concerned entered the value. Seven. If you plan in using a lot of silicon sealant and you're confident you are going to make a new air tight box, go ahead an intra Curiel of 15. Here you can enter the box volume and tuning frequency as you like, and adjust accordingly until you get the desired frequency response curve. So let's say we want to tune it toe 30 hertz. Let's under 30 Hertz joining frequency. And judging by the V s value, let's start with something like 40 leaders and the curial of ah seven with normal losses. As you can see, we have a peek off around 1.5 db. If we keep increasing the volume, we will get a better with free in a larger and larger peak. So if we moved from 40 toe 50 you can see how the response curve modifies. You can see the P getting larger. So for 90 leaders even higher, peak for 100 even higher peak at 100 leaders. We already have a three DB Peak. That's why, for SPL competitions, the boxes are huge. The linearity is not the factor on Lee. How much some pressure they generate is important. So having a large speaking that response is desirable. This is one way to design a box by changing values off the volume and tuning frequency until you get the response you are satisfied with. Alternatively, you can choose. A base reflects the line one. When you enter the speaker parameters, you can observe the values for different base reflects laymance. So, for example, if I want a maximally flat response, I should go for a Q B three alignment. Let's say I'm confident I'm going to make an airtight box so I choose Que El Off 15 simply entered those values in the box parameter section. So we have the volume move 65.82 liters. Cuba is 15 and the F B is 24.34 and there you have it, a maximally flat. The response. Now let's see the difference between box losses. Let's try a 60 liter box with the tuning frequency off 30 hertz. What happens when we change the box losses from 7 to 15. You can see we gained an additional one db in the response. It has the same effect as if the box is larger. So a box with a que well off seven has the same effect with a slightly smaller box. But with the Q well of 15. So if you make the box less leaky, you effectively gain some free volume. Let's design an actual box for the speaker. So considering we want a Q B three alignment, let's enter the box parameters with a que l of 15. So again Ah, 65.82 the F B's Trench 4.34. Let's move down to poor design number of ports. Let's go for one port, and the diameter needs to be at least 10 centimeters. Recommended would be 15 centimeters diameter. So if you go for 150 millimeters, the length is 1.2 meters, which is pretty long. So let's make a compromise and go for a 10 centimeters port. Now we have, ah, 50 free centimeter long port, which is more manageable. E. For example, you want to place to ports, so the number of ports now is to so two ports off 10 centimeters diameter each. The port length needs to be 1.1 meters. Please know that this length is for each port, not the combined length. So each port needs to be 1.1 meters long, so adding an extra port poses some extra difficulties. What I want to show is that the box volume is in direct correlation with the length of the port. So if you enter the speaker parameters and see that the Q B three alignment demands on Lee , let's say 20 liters of volume. Don't be smiling just yet because smaller box volume demands a longer port. So if I change the box volume 20 liters watch what happens. So all other factors remain the same Onley. The box volume has been reduced to 20 liters in return, the length of the port or ports because we have to has increased from 1.1 meters to 3.9. That's a ridiculous port length. To reduce the port length, you have to choose a smaller port or choose a higher tuning frequency. So if we tune it higher, we can see that the port length starts to go down. So the junior frequencies 24. If we go into 25 26 you can see it going down. 27 30 Hertz 40 50 against yet 50 hertz. We have, ah, 87 centimeter long port or ports because we have two ports. Try to ignore the frequency response chart. I'm just trying to make a point on how these parameters direct with each other. If you want to design a rectangular port, it's basically the same thing before. A dangler port has the same Miria of a circular port. The length should be the same. That's why I included an equivalent diameter calculator so you can make an idea on how large the sport would be if it were circular. So let's under the Q B three numbers so we can work with real world values analysts which the number of ports to one in the round section so entered the Q B three values 65.8 to 12 15 24.34 hurts and one round then centimeter diameter port. Now let's design a rectangular port Number of ports. One. I really don't see why you would have to, but anyway. If the speakers 12 inches, let's say the height is 30 centimeters, so 300 millimeters and let's go with the width off 50 millimeters. The equivalent diameter is 138 millimeters, so bigger than the 100 millimeters round port, and the length is about one meter long. When working with rectangular ports, it's easier to fit longer ports. This is because you can use them in an L shape or if it's too long, you can make elaborate to make efficient use of space.
34. 9.5 Bass reflex enclosure design using the paid application: designing a ported box using so before design toolbox should be pretty straightforward. Now go ahead and enter the three speaker parameters. So we have the FS off 24.2. The Q. T s 0.39 in the V s in leaders is to 4.1. After that. Select the ported enclosure type. Since this app has no option to select box losses or que well, we assume that Q. Ellis seven. You can see at the bottom. You get the recommended voting for a Q B three alignment and a recommended tuning frequency that turning frequencies just a recommendation. And sometimes it does not reflect the Q B three alignment. If you want to make sure your boxes online correctly, please use the alignments calculator in the Excel spreadsheet. But if you want to use these numbers, go ahead and double click them and the values are. Insert automatically in the box volume and tuning frequency section, and then you can go ahead in Click Update plot to view the frequency response chart. Now you can alter the box movement to need privacy as you wish, but we already done that using the spreadsheet So let's move on to port design. As we establish previously, the poor dimensions are in direct correlation on Lee with the box size and the tuning frequency. So we need to input these values. Head back to the book. Designing copied these two numbers. So we have the box volume of 68.59 leaders, 68.59 liters and the tuning frequencies 24.2, 24.2 hurts. Now you can select the type of port, and we have round rectangle and slot board. Let me show you an example for each one. If you go for around port, if the diameter is our 100 millimeters, then the length is calculated. Toe 514 millimeters. If I choose the poor Toby rectangle in shape, I have to enter the height and width. Let's a have a port off 35 by 250 millimeters. Then the length needs to be 577 millimeters. And finally, the slot board. The SLA port is basically a rectangle poor. It's very popular because it shares parts of the enclosure in the actual construction of the port, so the actual height of the port is fixed by the height of the enclosure, minus two times the thickness of the boards were using to make the enclosure. From a mathematical standpoint, it is basically a rectangular port, So if I enter the same values as before 35 millimeters by 250 millimeters, the length needs to be 560 millimeters, which is a bit shorter than the normal rectangular port. This is because the thickness of the front baffle is also used in the port construction, so the total port length is the actual length plus the thickness of the battle. Now let's move on toe the enclosure designed tab. When you are designing an enclosure, you have to calculate the total volume of the box first, which is the net volume plus the volume displaced by the speaker, plus the volume displaced by the port. Now, we previously calculated that the net volume is 68.6 litres. The volume displaced by the speaker is not coated by the manufacturer, But since it's a 12 inch wolf, or we can make an educated guess that it's roughly two leaders now let's calculate the port volume. Let's choose the round design with the 100 millimeters diameter. So with the length off 514 millimeters, the volume of the port is the area off the circle times the length. So the area of the circle is pi times the radius square, which is equal to 7850. And this we multiply by the length, which is 514 and we get roughly four million cubic millimeters now. To transform the volume into leaders, we need to transform millimeters into destined meters. Since we are talking in cubic units of measurement every step up in a subdivision, we have to divide by 1000. So if we round the number 24 million four million cubic millimeters are equal toe 4000 cubic centimeters, which are equal to four que big Desam eaters, which is four liters. So the total volume is equal to 68.6 plus two liters plus four leaders, which is the Goto 74.6. So we entered the volume 74.6 litres. As with the sealed enclosure entered the world thickness. Let's go for 22 millimeters now 22 and enter two dimensions, as you wish. But keep in mind the size of the speaker because it does need to fit. So, for example, the height I wanted to be 340 millimeters in the length I wanted to be 440 millimeters and hit the button Kilcher next to the dimension you need to calculate. So the box needs to be 680 millimeters deep click show template. And now you have your speaker box plans and you might as well start building.
35. 10.1 Construction tips - General: in this last section of the course, I'm going to talk about the best practices when it comes to building an enclosure. Then we're going to design a sealed enclosure from scratch and do the same for a base reflects enclosure. Let's begin by choosing the material for the enclosure. The most popular material for building enclosures is MDF, because it's a very dense and heavy. The surface of the material is very smooth and gives little headaches when applying of finish to the box. The cost of MDF is a relatively cheap compared to what it offers another popular choices. Plywood. Now, depending on the type of plywood, it can be cheaper or more expensive. Comfort. NDF plywood is stronger than MDF, and it's better suited for high powered speaker, or you can use thinner material for more common applications. A cheaper alternative is particleboard. This option is popular in budget applications, where standards are low. These are all materials that are made using pieces of dried wood and glued together in one form or another. Using role would is a bad idea. Even if it's dry, changes in humidity will occur, and as it ages it can warp and ruin the enclosure. Depending on the power of your speaker, you should choose an appropriate thickness for your enclosure walls. Most common used thicknesses 19 millimeters or 3/4 of an inch. You can successfully use this for drivers upto 500 watts. If you plan to go up in power, make sure you use thicker walls. Also, for one kilowatt used at least 22 millimeters MDF if you plan to go higher than two kilowatts. Ah, good idea. Used to use plywood instead. Birch plywood is a good chase, and as a general rule the thicker, the better as it reduces resonances. But bear in mind that thicker material will be more expensive, and it will make the enclosure very heavy. Another popular practice is to use a double baffle. You can see in the first picture that the holes are cut for the speaker and there another two holes for the ports. The glue is already applied. Then another panel identical with the battle is stuck on top. This one is screwed to the box and hold with a clamp in the middle until the glue dries off . Since we are cutting a big hole in the baffle to fit the speaker. We are severely affecting its structural integrity. Most of the time for based reflects enclosure, the port will be placed on the front baffle. Also, in this case, we have two of them. The additional holes will hinder the strength of the baffle even further. To compensate for this, a double bed feliz used stacked two boards and glue them together, and you got yourself a double battle. As a result, the front panel who have double the thickness compared to the rest of the panels used to build the enclosure for lower power projects like 100 and 200 watts. This is not mandatory toe fit. The panels together use wood, glue and clamps to keep the panels in place until the glue dries off. Sometimes crews are used in conjunction with blue. It makes the enclosure more 30 and you don't need clamps anymore. Please know that the glue is the primary factor that keeps the enclosure together, not the screws. Also, it acts like a ceiling for the joints of the enclosure. In a small two way enclosures. Screws are almost never used because it's harder to make the enclosure look good and apply a decent finish to it. When working with MDF. Making pilot holes for the screws is mandatory. The material is very dense, and if you screw the screw directly into the material, it will crack. Now let's talk about choosing panel dimensions when constructing a box. Are the dimensions of the panels relevant or it doesn't even matter? Well, it actually does. It has to do with the internal waves, more so with internal standing waves. A standing wave is a wave that takes a lot of time to dissipate its energy. This happens when bouncing back and forth between peril Walls. A rectangular books, has three pairs of parallel walls. Let me describe the perfect environment for a standing wave. We already established that two parallel walls is a good place for waves to bounce back and forth. If the distance between these two walls is half the way bling off the frequency off that particular sound wave, it will bounce back and forth with the little consumed energy. Let me make an analogy if you take a rubber band and stretch it. If you pinch it from the middle, it will keep vibrating for longer. If you paint it from closer to the ends, it will not vibrate as much. Different frequencies have different wave lings, and some will match this criteria that the distance between the walls is half of wavelengths. Also, multiples of this will work as well. So half of wavelength 1.5 wavelength 2.5 and so on. If this condition is satisfied, that particular wave will bounce back and forth between the walls for a longer time compared to the rest of the frequencies. Even after the speaker has stopped receiving the signal to stop panel resonances, we can do several things. Don't make a rectangular box. A trapezoidal shape is a better choice as it forces the wave to take non uniformed paths. The more angles the enclosure has, the better the worst case scenario used to make a Cuban closure. This is because you will have the same standing wave from the back top to bottom and left to right. They will reinforce each other, and the box will probably ring at that frequency a good rule of thumb. If you divide the internal with length or hide by one another, make sure you don't get the whole number. While it is not mandatory, you can use a golden ratio. The following ratios for internal box dimensions are considered have the lowest the resonances. So here are different ratios, So if you choose the first ratio and let's say you choose the with for the box to be 230 millimeters, then you can calculate the height as a 230 times 1.17 which is equal toe 169 millimeters and the length is 230 times 1.47 which is equal to 338. Please know that these are internal dimensions. Also, please note that this ratios are best sound wise. The enclosure will look a big awkward as, uh, it's not the most proportionate. From a visual standpoint, internal bracing can also help. Bracing of the panels can be done in many different ways, and it's up to your imagination on how you do it. Also, it's up to you on how much you want to complicate the design. If the box is small enough, you can choose not to brace it, or you can choose some simple, bracing techniques. You can use the pieces of wood. Cut that 45 degree angles to brace neighboring panels. You can use triangular pieces of wood took place in the corners. You can use the rectangular pieces as well. The effect is the same Onley problem is that they buy more internal ball. You you can use bracing the size of a panel, but with holes in it. This is very effective because it holds together the whole enclosure from the middle. Also, you can up for a more complex and creative bracing patterns. Now let's talk about the port. Design doesn't make any difference on which panel I place the port. Most of the time it doesn't, but it depends on your application. Ideally, you want to place the port on the same panel with the speaker, so they radiate sound as close to each other. It's possible, I say, ideally because base has very long way. Billings, so being a bit apart won't do much to the overall sound. But here are some scenarios where you would not want to place the port in certain areas. Let's say you have some small bookshelf speakers that you want to use for your computer, but considered they are of decent power. You wouldn't want to place the port on the front panel because it could blow annoying air into your face. If you plan to position your speaker against the wall, you wouldn't want to place the port on the back panel. This is because it could choke the port, or it can make unwanted noise if it's partially obstructed. Sometimes the port is placed on the bottom panel. This is considering the speaker has some sort of feet. Placing the port at the bottom or at the back has some benefit. If it higher volumes, the port is a bit noisy. The noise can remain undetected if the port is not firing directly at the listener. Placing the port on the top panel is rarely done, and I myself have been seen such design, but I'm sure it exists well. There's nothing wrong in placing the port upward. It makes it easier for us to settle inside the enclosure. Let's talk a bit about the cylindrical ports. When you are feeding a port inside a box, you must be careful that the other end of the port is not too close to the internal walls off the enclosure. This distance must be at least the size of the diameter of the port. So if the diameter of the port is 10 centimeters, make sure that the other end of the port is at least 10 centimeters away from the inside war. This issue is sometimes sold by using a 90 degree elbow. Also, when fitting a port one enclosure, it is important to know that you don't have to fit it inside the box. While this is more convenient than better looking, you can hope to place the port outside the box. By doing this, you don't have to add the volume displaced by the port to the overall internal volume off the box. When dealing with flair ports, you have to consider the length of the flares. Also. Now this involves complicated formulas, depending on the growth of the player, which would be quite difficult to measure. But as always, I like to simplify things, which makes calculation easy and the results good enough after you calculated the length of the port, including the total length half of the length of each player. So if the length of the port needs to be, ah 150 millimeters, and you have to 40 millimeter long flares. The port will be made by a flare at one end, 110 millimeters long pipe and another flare at the other end. So 20 plus 110 plus 20 equals 150. If you have only one flare at one end, it's one flare plus 130 millimeters pipe. Now, when you're making rectangular ports, you can make them quite long adopting two techniques. You can make an L shaped port. This will give a pretty decent Portland, but it's limited to your enclosures with in depth. If you want to make an even longer port, you can make elaborate. By doing this, you are making the most out of the available space, and you can make a very long port in the least amount of volume for the last two sections. Off this course, I'm going to give a four start to finish example on how to build a sealed enclosure and a base of freaks enclosure. But first we need to be co driver. There are a few tips when choosing a driver for a sealed or based reflects enclosure first is to calculate the E B P or the efficiency. Bend with brother if you divide the drivers FS or resonant frequency by its Q. Yes, you will get the CBP Val. If it's lower than 50 the driver is more suited for a sealed enclosure. If it's between 50 and 100 the driver is suited for both. And if e B P is higher than 100 then it's better off in a based reflects enclosure. Another quick way to tell which enclosure is best for a particular driver is to look at its Q T s. If it's 0.4 or lower, it's more suitable for base reflects. If Q T s is between 0.4 and 0.7, then you might consider a sealed enclosure. If you d S is higher than 0.7, then an infinite baffle would be more appropriate. While these are some general rules, they're not set in stone. For example, you could use a speaker with a Q T is off 0.5 in any type of enclosure. However, when we are talking about the extremes, you should follow the rule. For example, a 0.3 Q T s speaker is not suitable for an infinite baffle enclosure. And at the other end of the spectrum, a 1.1 cuties driver, for example, is definitely not suited for a base reflects enclosure for our two enclosure. Examples sealed in base reflects I'm going to is a driver, which is suited for both. I chose a 12 inch jail will for And if I calculate the e b p. Here are the parameters of the speaker. An e B P E is equal to 26.99 divided by 0.487 So F is divided by Q years, which is equal to 55.27. We get any BP off 55 which states that it is suitable for both type of enclosures, with the slight bias, the wars, the sealed enclosure
36. 10.2 Construction tips - Sealed design: We're going to calculate the sealed enclosure using the Excel spreadsheet, so go ahead and copy the parameters. So the FS is 26.19 to the Q T s. 0.46 NVs is 54 point 37 liters. Now I'm going to choose a Q t C off 0.8. This is for a slightly smaller box, but with a bit more punch and with decent but not perfect linearity. So the Q G c is a 0.8. This means the volume needs to be 26.86 leaders. Now, this is the net internal volume off the box and I'm gonna show you here in this, uh, side the worksheet. What calculations have I done to fully designed the box? So as you can see at the top, we have the net volume off the box. But let's do this by the book. Let's add the volume displays by the speaker and the volume displaced by a few bits of bracing elements I'm going to use to brace the box. Fortunately, jail quotes the volume displaced by the speaker, which is 2.97 liters and also I'm going to add up the bottom, displaced by the bracing, Let's say, 0.5 liters. This is depending on how many you have and how big they are. You can easily calculate the volume, so they all add up to 30.30 free leaders. Now we are going to feel the box with sound dampening material, and we know that by doing that we will gain about 10% of perceived volume. So we need to compensate for this. We need to make the box 10% smaller. So if we take 10% away from 30 leaders born 33 we get 27.57 leaders. So the box needs to have a volume off 27.50 several leaders. No, let's design the actual box for this example. I'm going to use a golden ratio, and I'm going to show you how to calculate the panel dimensions according to this ratio. So the volume is 27.57 leaders. Now we have to transform this ratio into a nick ways Asian. If we multiply each one of them, we should get the volume, so x Times 1.26 6 times 1.60 x should equal to the box volume, which we will transform in Q big millimeters, which is 27 million, 570,000 cubic millimeters. Now, after you have done the multiplication, I'm going to show you how you can extract the cubic root because you have X at the power of three. So let me bring up the calculator. We have 27 million, 570,000 which we will divide by 2.16 so x at the power of three easy will do this number. So what? We extract the cubic root. We set this number to the power off one divided by three and we get 239 millimeters. So X is equal to 239. By knowing next, we can calculate the other dimensions by multiplying with the numbers of the ratio. So 239 multiplied by 1.26 is equal to 301 millimeters and set is equal to 239 multiplied by 1.6, which is equal toe, 382 millimeters. So now we know the internal dimensions of the box, and we can verify this. If we multiply these newly calculated dimensions, we get a volume off 27.48 leaders, which is roughly equal to 27.57. It is not exactly that because I rounded up the numbers. Now let's have a look at the physical dimensions of the driver, and we can see that the outer diameter is 318 millimeters. At first glance, this driver is too big for our box. We need to dimensions with at least 318 millimeters toe fit this speaker, and we only have one. But these are the internal dimensions. To calculate the external dimensions, you need to know the thickness of the panels For this driver. I recommend using 22 millimeter boards to calculate the outer dimensions off the box. You need toe. Add two times the thickness of the board toe each dimension. So by knowing the internal dimensions, you add the double of the thickness of the boards, which is two times 22 so 44. By adding 44 to each of the internal dimension, you get the external dimensions of the box. Now against you have two dimensions which are bigger than the outer diameter of the speaker . With just 318. Those two dimensions will be the width and height off the box. The last one will be the depth. Now we need to check the depth of the speaker to see if it fits. The depth is 191 millimeters. Any definitely fits another thing we need to check. Since the outer diameter of the speaker is larger than the internal size of the box, the mountain hole diameter needs to be smaller than the internal dimensions. And since it is 218 it is smaller than both 301 and 382 so the speaker will fit inside the box. Now we need to calculate the sites of the panels. Since we know the internal dimensions and the external dimensions of the box, this should be quite easy. Now I'm going to put this exploded diagram off the enclosure on the screen as reference as you can see. The front and back panel have the same dimensions as the outer dimension, so 345 times 426. For the top and bottom panel. You have the full exterior with but the internal depth. So these panels are 239 times, 426 and the sides have the same dimensions as the internal warms. So 239 times 301 you need to pieces off each of these dimensions, so six boards in total, and you can go ahead and start building your sealed enclosure.
37. 10.3 Construction tips - Bass reflex design: now for the base for Felix enclosure. We're going to use the same driver, but now we are going to design it. Using the subwoofer design toolbox sees the circular port would be easier to do. I'm going to show you how to make a slot. Port subwoofer This happened doesn't have a Curiel option. So considering Toby seven and I'm not going to use in your line, I will design the box by trial and error until I get a desired modeled frequency response. The end goal is to have a low tuning frequency and a plus two db Peak. I want us upto hit hard and low given that the linearity will not be perfect. First of all, Kobe the three parameters and select ported. So the if s is 26.92 the Q T s 0.46 the V s in leaders is 54.37 and portend enclosure. Now I'm going toe double click the recommended values by the AB and start from there. Go ahead and click up the plot and you can see we got a very flat response. But we are aiming for a plus two db So let's increase the box volume toe 100 and 20 liters . Now let me full screen this so we can look a little closer. You can observe that we gained just a little bit of output. But if you look closely, you will see that the response is going down and then going up again, and then it starts to roll off. This is happening because the boxes june too low below the resonant frequency of the driver . Well, this is quite the common practice. Going to low can have this effect. So let's try to increase the resonant frequency by just a few clicks. So now it's almost 20 free. Let's Goto 24 the plot 85. No, you can see that we already hit our goal no more deep in the response below the resonant frequency of the speaker, and we got a to the B peek at the resonant pregnancy off the box. If you want, plus three db, you could increase the box, vault him even further. But that is not our interest. Now let's go ahead and designed. The port entered the box numbers so 120 liters and 25 hertz and select the rectangle. Since we know that the speaker has an outer diameter of 318 millimeters, I'm going to choose an enclosure that will be 400 millimeters tall. So I don't have any fitting issues. Since the thickness of the panels will be 22 millimeters, the port height will be 400 minus 20 to minus 22. So 356 millimeters. 366 for the poor to have with this interior off 40 millimeter wide port should be more than enough considering its height. But I'm going to go for 80 millimeters to make it ridiculously long and make the enclosure more complicated. So 80 millimeters with so the length of the port needs to be 1002 millimeters. Since we're going to cut a rectangle in the front baffle to accommodate the port, the thickness of the baffle takes part in the total length of the port. From the actual length of the port, you will exclude the thickness of the baffle. But since we're going to make a double baffle, subtract two times the thickness of the baffle from the total length of the port, so 1000 to minus 20 to minus 20 do, which is equal to 958. In conclusion, the port needs to be 356 millimeters told by 80 millimeters wide and 958 millimeters long. Since we know the dimensions of the port, we now need to calculate the total volume it displaces. Three sides of the port uses actual panels of the enclosure, but the fourth is added extra and needs to be taken into consideration for volume displaced . For added simplicity, consider that the width of the port is the actual width plus the thickness off this panel. So 80 plus 22 which is equal to 102 millimeters. So the volume displaced by the port is 356 multiplied by 102 multiplied by 958 which is equal toe 34 points. 79 Leaders of volume. Now we have to add up all these volumes. So the net volume, the volume displaced by the speaker, the port and the brace ing's. So 100 and 20 plus 2.97 plus 34.79 plus 0.5 liters, which will be the brace ing's, which is equal to a total off Ah 158.26 leaders. Now let's go to the enclosure design. We know that the wall thickness will be 22 millimeters and the volume we calculated at 158.26 leaders and also we established that the height is 400 millimeters. Now the depth needs to be a minimum of 190 millimeters, considering the mounting death off the speaker. But since the boxes very large, we need to go for a bigger number than that. I was thinking something like 550 millimeters to minimize standing ways. Let's go for a number that is not round so 500 53 millimeters, so 553 millimeters and now we calculate the with, which is 917 millimeters. Now, if you click short template, you have all the pinal dimensions and you can start building the box. But let's focus on the poor design. Now we have the outside dimensions off 917 times, 400 times, 553. You can observe the various bracing elements now because the port is long. I opted for an L shaped design. Observe the double baffled, which contributes the total length of the port. So does 44 millimeters and we need to come up with the rest of 958 millimeters. I understand that the second front baffle is applied after the boxes done. So the actual depth of the boxes now 553 plus 22 575 millimeters. The port is 80 millimeters wipe. So this section is 80 millimeters if we substrate from the total length 575 minus 44 the double baffle and minus 22 the back panel and this 80 millimeters from the other piece of the port. We are left with 575 minus 44 minus 22 minus 80. We got 429 millimeters. So the first panel is 429 millimeters long. The height of this panel is the actually internal height of the box, so 400 minus 20 to minus 20 to 300 56 millimeters. So this panel is 429 times 356 millimeters. This means that this section has the rest of the length of the port, so 958 minus 429 That's 529 millimeters. So the length of the second port panel is 529 minus 80 millimeters the width of the port minus 22 millimeters. The thickness of this panel, which is equal to 427 millimeters. So the second panel is 427 by 356 millimeters. If you look at the actual numbers, this drawing my look out of proportion. But this picture is just have a visual aid on this slot port design. Having said that, this concluded our enclosure designed course. Congratulations on sticking to it up until the end. I hope I had a clear explanation on the matter. But if you have any questions, don't hesitate to contact me
38. 11.1 2-way design Introduction: This is the first update for discourse because I received feedback that people wanted more info about multi way speakers and that the course only offers information on how to build a subwoofer. This is partially correct. The course is about how to design an enclosure. This is, regardless, if it's one way to way and so on. The problem with multi way speakers is that you need to design a crossover for them. The crossover design part is quite challenging and by far the most difficult part in making a speaker system. To make a good crossover design, you have toe have the equipment necessary to measure the frequency response, the impedance and then RLC meter. To measure crossover components, you have to learn how to make quasi and a quick measurements. You need a room that is sufficiently large enough to make these measurements. You need to learn how to measure feel small parameters. You need a crossover design software that will help you in optimizing the response curves in. These are just the things that came from the top of my head in conclusion. To make a crossover, you need adequate measurement equipment than software. Also, it will take it least I don't know 10 hours to describe every process. If this should be of interest, most definitely it will be in a separate course. So if you are interested in this complex course about crossovers, make sure you let me know and support me with the five star Review. However, even if you are a skilled electrical engineer and make a great crossover, you still need to design the enclosure, which this course is all about. The enclosure dictates the Loman response off the speaker system, regardless, if it's a subwoofer or a multi way loudspeaker. In other words, bad enclosure, bad based response. Also, if you want to design a crossover, you would need to take this course beforehand, as the acoustical part is interconnected with the electrical part. Anyway, I felt the need to have a section to this course regarding full range loudspeakers, so I will show you the design process of a two way bookshelf speaker. As for the crossover part, I will attach an Excel spreadsheet, which will calculate the basic crossover and buy basic. I mean that it will do nothing fancy. It will separate the frequencies between the Tweeter and Mitt base and make sure that we there won't burn up. I will also show you the difference between this simple crossover and another which more effort has been put into it.
39. 11.2 Enclosure design: we're going to make a two way bookshelf speaker with the rear firing bass reflex port. The Twitter is a refer X T 25 very popular Twitter in the D, A white community, as it offers a great value for money. And the mid base is a safe C 18 R N X, a seven inch driver, a good base draper, but a bit more pricey. The drivers are not expensive, but not cheap. Also, this is going to be a moderately price project now. I'm not going to use the TS parameters provided by the manufacturer because I have the means to measure them. That doesn't mean that the numbers you find the specifications sheet that wrong is just that you get the more accurate number if you measure them. You have to understand that although the manufacturing process is the same, it's not uncommon for speakers to have a deviation from the numbers you found in the specifications sheet, especially for the cheap drivers. While not something to show us about. If you can measure the two years parameters, you might as well do it. So we have the FS off 39 hurts the Q t s 0.32 the VSC s 24 liters. If you enter these numbers in the Excel spreadsheet and aimed for a Butterworth response, so let's enter the parameters. We have 39 hertz, 0.32 24 liters. We got the Butterworth response that 10.14 leaders cool off seven and the resonant frequency off the box said 48 at 48 hurts. This will demand one single port off 50 millimeters, so the length of the port will be 216 millimeters. Now this is all fine on paper. But when you factor in the size of the baffle to accommodate the two speakers, there isn't enough depth to fit the rear firing port and also to leave appropriate breathing room for the port. So it's not choked at the other end. So to give you an example with external dimensions, a large enough baffle toe feed the speakers will be something like 320 by 220 millimeters. Having this prayerful will demand a depth off 230 millimeters to reach the 10 litre volume , so there isn't enough room to fit the port and leave any breathing room. As a result, we need to scrap the Butterworth response and make the enclosure bigger and work our way from their Ah, 50 littering. Closure will be more appropriate. Also, I'm going to turn it a bit higher in frequency at 50 free herds to get a plus one to be peak for a bit off extra kick. For this tuning frequency, we need the 50 millimeter diameter port off just 104 millimeters in length. A bigger enclosure gives us more room to work with, and the extra volume will demand a short port, which makes our lives but more easier. As you can see, I mentioned nothing about the Twitter. This is because the enclosure is solely for the mid base that Twitter does not need an enclosure. Furthermore, the Twitter is encapsulated and it's not affected by the motion of the buffer. However, in a multi way set up, the story is different. Let's say you have a three way set up with the war for a mid range driver and a Twitter. We know that the tweet there is encapsulated, so it poses no problems, but the midrange driver isn't There is an issue here because the mid range shares the same enclosure with the wolf for the wolf for motion will force unwanted cone movement for the midrange driver and introduce distortion. For this reason, we need to make separate chambers. The usual solution is to place the wolf wearing toe one chamber in the mid range of the Twitter into another chamber. The chamber for the mean range should be sealed. Enclosure. Don't bring any fancy enclosure here because you probably will do more bad than good. The size of the enclosure does matter. Depending on hollow, the mid range will play and how well you want to damp it. Exactly as we talked about in the sealed enclosure designed section on Lee, the resonant frequency will be much higher now. The chamber for the wolf for is separated, and you can make it. However you wish sealed base reflects, or any other type of enclosure you might fancy another soldier. She needs to make a separate enclosure for the mid range alone, either by using pieces of wood or buying special cups that seal the back of the mid range driver. Some mid range speakers, especially dome speakers, are encapsulated just like the tweeters. So one less thing to worry about. The main thing you need to focus on is the base driver. This is where the inclusion will have a considerable contribution in the low frequency department. We already established that the enclosure will have a 15 liter volume, but that is the net volume we need to start adding the other components which we will fit inside the box. So the net volume is 15 litres. The port will be around 0.25 the speaker 0.35 liters, the crossover 0.2 and the bracing 0.4 liters. This adds up to a total off 16.2 leaders. Now that we found the overall volume off the box, we need to calculate the dimensions of the panels. And because the enclosure is pretty small, we need to focus on two things. Make sure that the baffle is sufficiently large enough to accommodate the wolf for, and the Tweeter, especially with wise, make sure that the depth is sufficient to accommodate the length of the port. In conclusion, the baffle needs to be large toe have enough room for the drivers but small at the same time, so it will demand a sufficient depth to reach the required volume. This is the make room for the port. If the battle is too large, then the enclosure will be shallow as we only need 16.2 litres of all you. A good choice for this type of enclosures is 3/4 of an inch MDF or 19 millimeters. Since I had some 18 millimeter MD of lying around, that was my choice. To make my life easier, I calculated the size of the panels using symbol for design toolbox. After a bit of fiddling, I ended up with these dimensions. So 340 by 227 millimeters for the front and back to 80 by 27 millimeters top and bottom to 80 by 304 millimeters The sides and the 191 by 2 80 millimeters The bracing. I will see you later on what I mean by this bracing. These are the Penhall dimensions and numbers. For only one bucks, we will need material for two boxes. The mid bass speaker has 176 millimeters in diameter. If we had two times the thickness of the wall. Ah, 176 plus 18 plus 18 equals 212 millimeters. This means we got another 1.5 centimeters of room to spare. But make sure you center the speaker properly so you don't run up into issues like the speaker hitting the side of the wall. Height wise, 340 is more than enough to feed the wolf for and the Tweeter. No calculations needed here. The death is 280 millimeters, which is more than enough to accommodate the 104 millimeter port with breathing room to spare. Now that be validated our panel dimensions. We should head on toe the construction.
40. 11.3 Enclosure construction: Cottle the panels the correct size, using whatever you have available. Handful table. So some hardware stores are for cutting services, and you can buy the panels directly at the right sizes. For the holes. Use a router with a circle jig. I off, said the tweeter, to reduce age diffraction. As for bracing, just cut the panel to the inner dimensions of the box, then make a large hole in. It doesn't matter the sheep or how well you cut it, because we'll be inside the box and no one will see it anyway. I drilled four holes using a large drill bit and then use the jigsaw toe cut between them and make the bracing. As for the back panel, cut the whole for the port and use the drill to make two small holes for the binding posts . For assembly, we will use wood glue on Lee. No screws are used. Just go everything up and secure with clams until it dries up. To put the bracing in place, I did a neat trick, which worked well with this project. I stacked little pieces of MDF until the bracing reached the designated height. This is so it doesn't obstruct the cut out for the meat base, the tweeter or the ports. After that, apply glue to each section, which comes in contact with another panel, only 11 site. Look at the enclosure designed tool box diagram toe. Understand how each piece stacks the one another next puzzle. The pieces together. I manage this by myself, but it's much easier with helping hands. First thing I like to do is use four clams in the corners of the sites. When you place the clamp, make sure it covers all the three panels, which make up that corner for the top corners. There will be only two panels because the top panel isn't place yet. Also, don't tighten the clamp all the way. Yet. After you place the four clams, you can go ahead and place a few longer clamps to secure the front and back panel again. Don't tighten all the way as the top panel is not placed yet. Take advantage of this and add additional glued to the joints where it's not losing out. This will make sure all the panels will stick together, and they are not leaking any air. After that apply grew to the top panel and place it on top. Place a big vertical clamp from the top to bottom, and now you can tighten each clamp until every panel is nice and snug. Leave it there for 24 hours. If you have panels that are not flush, use the center to correct the imperfections and to assure that the box has a small with finish. As for the port, if you buy a high quality one, it will be made by several pieces on inner Flare. A long pipe, which you can cut the size two connection rings in the outer flare. After you cut it to the appropriate size, disconnect the back for an apply cocked to the side, which will fit to the box. I usually like to go overboard here and remove the excess after it has dried up. This port doesn't have school horse to fix it to the box, and if it's any bid loose, it will introduce unwanted distortion. Even if the hole is cut, processed it to size and you force the port in, I will guarantee it will still have air leaks. The vibrating air from inside the box has its ways to come out for the small imperfections and make the port on stable increase distortion. That's why I don't like to take my chances. But going for a small quantity of silicon should be fine. Also, the binding posts are just some fancy bolt and nut system. Place them in the holes and screw the nut from the inside of the box until the terminal is secured firmly to the box. Then we will use some cream terminals to connect to the binding posts.
41. 11.4 Crossover basics: as I mentioned before. This course is not about crossover design because the subject is too large and demands a separate course. However, I will touch the subject briefly and explain things as simple as possible. A passive crossover network is a collection of capacitors in doctors and resistors To simplify things, the components have the following properties. Capacitors repel low frequencies in doctors, repel high frequencies and resistors repel all frequencies. You might have heard of simple solutions, like placing capacitors in series with a twitter so you don't burn it up. This is because the capacitor filters the base, the low frequency notes. Or you might have placed a series resistor with a twitter toe. Take me down. Since it filters all frequencies in, basically lowers the output of the Tweeter. Of course, the value of the resistor dictates how much of this effect will take place. And, of course, the value of the capacitor. And in Dr the Germans, which frequencies are filtered more of that later. The crossover have many types, depending on which characteristics you are focusing. So if you are talking about the filtered frequency, there are free types, high pass filter filters, the low frequencies and lets the high frequencies past used for tweeters. So if you look at the frequency response, the high frequencies are untouched. And then as it reaches the lower notes, the output gets lower and lower as the effect of the filter starts to Syrian. The point when the response starts to roll off, also known as the crossover point, will be different, depending on the values of the components. Band pass filter filters, some low frequencies and some high frequencies used for midrange drivers. Low pass filter filters the high frequencies and lets the low frequencies pass used for wolfers, while filtering the base from the Twitter is a must tow, make sure the driver doesn't fail. Having a wolf for playing high frequency sounds won't damage it in any way, however. Sometimes you have to filter of the high frequencies from a wolf for so you don't end up with too much high frequency response. When that Twitter is playing the same frequency band, one other purpose of the crossover is to make sure that the frequencies of the wolf for and the Twitter blend will and some upto a flat response. One of the key defining factors off this summation is the knee of the response that roll off the cue of the filter describes the shape of the knee when the frequency starts to roll off. The Q shapes are exactly the same as the Q T C discussed at closed box. This means that the queue of 0.7 will give the longest linear response before roll off, while a cue off one will give us like big before roll off. Also, the different values off Q have corresponding names, which will almost always be used, so a queue of 0.49 is liquids. Riley Que off 0.58 is basil Q of 0.7 or seventies Butterworth and cue off one and above his chip ship to translate this in plain English link Israeli crossover matches the Attenuation slopes, so they combined for a flat response at the crossover point. Butterworth crossover creates a small peak in the response at the crossover point. Best sell crossover is somewhere in between the 1st 2 and the chip Schiff basically avoided a zit greets on unwanted peek at the crossover point. You may be confused, but I'm not stressing too much on this is we want to design just a basic crossover and this won't be a barrier. So so have a bit of patients. The crossover orders It's the roll off slope. The most popular ones are 1st 2nd 3rd and fourth order crossovers. First Order has a six db per octave slope. Second order has a 12 db per octave slope. Third order has 18 db in fourth quarter has 24 db per octave slope. The order of the crossover lets us know the amount of components in the circuit will have. These are the number of components for each speaker side, so First Order has one component. Second order has two components. Third order will have three components and four for there will have four components, depending on the crossover order. There will also be some face shift. Different types off crossovers will result in different face relationships between the drivers, so first order presents the high pass and low pass in a 90 degree out of phase relationship . Second order presents the high pass and low pass in on 180 degrees out of phase relationship. So basically you need to reverse the polarity of the Tweeter so they don't cancel each other out at the crossover frequency. Third Order presents the high pass and Lopez in a 270 degrees out of phase relationship. Many choose to do the same polarity, switching off the Tweeter in this case shifting toe 90 degrees out of phase. And the 44 order presents the high pass and low pass in a 360 degrees out of phase relationship, which is basically in face but with one delayed cycle.
42. 11.5 Crossover design: Let's open the attached Excel spreadsheet in Designer Toe Way crossover. I hope you already learned my style, and you already know that you have to enter the values in the orange sells and ignore the rest. You only have to input the impedance of the treater, the impedance of the mid base and the crossover frequency. After that, it will display the value off each component of the crossover. Several popular crossover apologies have been chosen. The problem with this kind of design is that these formulas consider the speaker like a resistor with the fixed resistance value. Now we already know that the impedance varies with frequency. Using the nominal impedance off, the speaker is basically cutting corners. Also, face cannot be predicted without measurement. Baffled diffraction is also an issue and much more. What I'm trying to say is that this is an oversimplification off a crossover network. It will protect the tweeter and separate the frequencies between the driver's successfully . But don't expect ruler flat frequency response anyway. People still use these designs. Sometimes it works very well because the design is very simple. Now let's return to our Excel spreadsheet, the nominally pittance of the drivers is found in the specification ship. So let's take a look at our drivers our way for Twitter has an impedance off forums, and the cess mid base has an impedance off eight homes. So, let's say, introduced them into the cells. Britches Forums for the Tweeter and A comes for the mid base. Now, to choose the crossover frequency, we need to take a look at the frequency response off both drivers. Let's start with the Tweeter. This is important as choosing a bad crossover point can damage the Tweeter. Look at where the response starts to roll off, which is roughly at 1000 hertz Go for a crossover point, at least an octave above that, So at least 2000 hertz. To be on the safe side, you can choose a second order filter at 2500 Hertz or a 44 there at to 1000 hertz. If you design a system that you know, you will play loud Ah, higher crossover point would be advised. So for now we know that the crossover point will be somewhere above two kilohertz. Now let's switch to the myth based response. This meat base has a pretty clear frequencies parts. More often than not, you'll see your cone break up in the response chart. We already talked about this. It will appear as a peak in the response as you enter the high frequencies. If so, make sure the crossover point is at least one octave below the cone break up. So if you see that the cone is breaking up at the six kilohertz trying not to cross the driver above three kilohertz, judging by the frequency response anywhere between two and three killers should be a great pick. Let's go for 2500 Hertz Crossover point Popular choice for crossover topology is liquids Riley because the two responses some of flat this is only available in even orders. So second for six, except for the simpler the crossover, the better because it has a lower component count. This means less stuff that can deteriorate the signal and, of course, a lower cost. We talked about the face relationship between the two drivers for the second order filters , and they are 100 and 80 degrees out of face, so you have to reverse the polarity of the Twitter so that the two drivers don't cancel each other out at the crossover frequency, so let's input the crossover frequency off 2500 hertz. Now you can see the values of the components for the second order link with Israeli. If you would use such a filter, the crossover frequency off the speaker would look like this. I actually made the crossover and measure it so I can see how the response will look like. Clearly, you can see that the tweet there is way louder as the high frequencies have a higher amplitude, However, not having the means to measure the frequency response. You cannot know this, but many times you can tell that that we there is harsh, and you can fix this by placing a series resistor on the Twitter side. Start with something like a three Yoma resistor and then play with different values until you find something satisfactory. This will lower the high frequencies and will yield a moral in a response just to make a comparison. If you have the necessary tools and know how you can make a significantly better crossover design, which could look like this. This is an asymmetrical crossover with the first order filter on the mid based side in the second order. On the sweeter side, it also features a leather delay network to match the acoustic centers off the two speakers and then Attenuation resisted. For the Tweeter, the frequency response will look like this clearly much better. The linearity is great, with only two db variation in the response. I'm just showing you what could be done because this course is not about crossovers. It's about enclosure design. The actual process off designing such a crossover, we'll have to leave it for another course.