It’s been 25 years since I wrote an article entitled “Exposing Acoustical Myths.” At the very top of the list was the misconception that absorption improves sound transmission loss.
And yet, rarely a week goes by that we don’t get a call from someone hoping that we can recommend some fuzzy material they can put on their walls to keep their neighbors happy.
Unfortunately, it doesn’t work that way.
The finishes on a surface determine how much of the sound that strikes that surface will be reflected back into the room, and how much will be absorbed. So yes, materials that are better at absorbing sound will soak up more of the energy. That can make a room a more pleasant place to work in, or a better environment for listening to music, or a space where you can carry on a conversation.
But you can’t make a space significantly quieter by increasing the absorption. A snare drum rim shot is still very loud, even in a very “dead” room. And if you have walls made of rice paper, it will be annoyingly loud for your neighbor, too.
The sound pressure level at a wall surface has a direct sound component that depends solely on the energy produced at the source and the distance from it. No amount of absorption can reduce the sound below that level.
At that point, how much the wall stops the sound from going through to the other side (it’s sound transmission loss properties) depends on the:
- Mass of the materials used
- Thickness and assembly of the barrier (including air cavities, damping, and other more esoteric properties)
- Control of flanking and structure-borne paths
It’s important to understand that room acoustics (how the sound behaves within the room) and sound isolation (keeping sound from getting in or out) are not the same thing.
And for good sound isolation there’s no substitute for heavy, airtight construction, regardless of how much fuzzy stuff you put on the walls.