This is the final part of our Why Room Acoustics is Very, Very Important article series. In the previous part, we covered what traits make a room ideal for listening. In this final part, we’ll discuss what changes you can make if your room doesn’t sound good.
Reflections and Dampening
In the first part of this series, we discussed audio reflections. Reflecting sound is sound that has bounced (like a ripple on the surface of water) off of a surface. Most often, in your room, the majority of reflected sound you hear will have been bounced off of the walls around the perimeter of the room.
Walls are practically always made from hard, rigid materials—and for good reason! This isn’t great for audio quality, however, because reflected audio sounds different when compared to the sound coming directly from the speaker. As I said in Part 1, if you’re standing more than two metres away from the speakers, at least 50% of the sound you hear is reflected. So, our goal is to reduce that percentage so that we hear mostly direct sound.
The simplest way to do this, is to treat the hard surfaces of the room with sound dampening materials. The most common choice is foam padding, which contains thousands of tiny pockets of air that help to trap sound waves, bouncing them over and over inside the material until they lose energy and dissipate. You’ll often see foam cut into spikes, or zig-zag patterns. This increases the sound-trapping ability of the foam, enabling slightly lower frequencies to become stuck too, endlessly bouncing to oblivion.
The corners of the room are almost always problematic for bass frequencies. The lower the pitch of a sound, the longer the wave is. This makes the tiny bubbles of air in foam pretty useless at containing bass frequencies (a low-pitched sound wave of 100Hz is approximately 3.4 metres long!). This makes the corners of the room act like the air bubbles in the foam. A build-up of bass in the corners. The solution? Make your corners less corner-y by adding bass traps.
A bass trap is acoustic treatment that fits into the corner of the room. It is usually in the shape of a triangular prism, with far more volume than the foam panels that are used on walls. The extra thickness helps to reduce the energy of low frequencies as they bounce between the hard surfaces of the walls.
There is a lot more that goes into treating a room acoustically, and I’m not qualified to write about it in much more detail. I would recommend reading up on resonance in rooms and Room Modes, here (http://www.acousticfrontiers.com/room-modes-101/ ) as a starting point. Good Luck!