Soundproofing

Soundproofing really can be broken down into two separate issues: sound transmission, and sound control. I’ll break this down into these two sections. This is not meant to be a complete treatment on the issue. There are many books and websites available, and I recommend "The Master Handbook of Acoustics", the Auralex website at www.auralex.com, as well as any other information you can get your hands on.

Section One: Sound Transmission
Basically, this is the boom boom boom that you hear from the car next to you. Sound transmission is reduced by the construction of the room, not by throwing something on the walls.
In a perfect world, you can construct the room from scratch. Here are some techniques: staggered beam construction, floating floors, drop ceiling. Here’s why you go through all the trouble. Sound waves are energy. Anything they hit, like a wall, they give some of that energy to the object. Now, laws of physics state that the energy doesn’t just disappear, it has to go somewhere. So that sound wave energy goes into the wall, then finds the next connection, like a beam, and travels along it’s length until it finds the next piece. The lower the frequency, the better it is at traveling along a solid object. At the end, it finds the last object (usually the wall facing the living room….) and that object gets deformed and re-broadcasts the sound wave into the next space. Higher frequencies get lost along the way, and that’s why you usually hear boom boom boom.
So for low frequencies, the trick is remove any connections. Hence the floating floors where the entire floor sits on hard rubber pads, and is separated from the floor underneath, and staggered beam construction, where the beams are smaller than the inner space of the wall where every other one attaches to the opposite wall so each wall does not have a path. Go online and find what this looks like. Now, lots of mass also helps with this low frequency problem. To get a little more dissipation, use at least two layers of sheetrock with two different thicknesses at 90 degrees to each other. It’s a long theory, but trust me it works, and sheetrock is cheap.
Now for high frequencies, think of your technique like preventing air from escaping. All the spaces in the walls should packed with standard R insulation (pink fiberglass), and any small spaces like the spaces around wall outlets should be filled in with the appropriate substance. If air can move through the space, then so can sound. The same goes for what’s over the ceiling: double and triple layers of insulation will tame the sound transmitting into those spaces, especially if there’s another room above.
Another reason to go through all this trouble is that you must remember you’re not just preventing sound from going out, you’re also preventing sound from coming in. If you’ve got live mics, then any sound that comes in will get picked up in your recording and will be permanently in the track.
Unfortunately, I’ll have to address the issue of sound control in the next issue. See you then!