If I could just draw myself that picture would be the perfect representation... I decided to keep it simple. hehe
The first thing I thought was the layout. A stressed layout can portray loudness. Other things that can come into play are big UPPERCASE letters, and colors (only thought about it since it is only a sketch)
These are things that, for me, represent the word LOUD:
A night in the CITY. 80s BOOM box. Police SIRENS. TROMPETS. FIESTAS!