The Two Secrets Of Soundproofing

While much of the art of acoustics is found in the design finishing touches that determines how a room sounds and feels, the hard science is in the basic construction which starts with some acoustic principles that provides the soundproofing ("isolation" is the more scientific term) that every studio needs.

Because most musicians and engineers aren't able to hire a real acoustician to design their rooms, they usually apply the only the finishing touches when they attempt to do it themselves while overlooking the basics, and their room never meet their needs in terms of isolation as a result.

That leads to the first question that both musicians and engineers ask regarding acoustics, “How can I make sure that my neighbors won’t hear us?” Here are the "secrets" of soundproofing, although they're really some basic acoustic principles.

First, all it takes is mass, which is our first principle. Simply put:

Acoustic Principle #1

The more mass your walls have between you and your neighbors 
(that includes walls made from cinder block, brick, wood, drywall, etc), 
the more you’ll be keep the outside sound from getting in, and the inside sound from getting out.

One of the ways that most pro studios accomplish soundproofing is by building a room within a room, which is done by putting the floor on springs or rubber, and building double or triple walls with air spaces in between on top. Needless to say, this gets really expensive and is impossible to do if you start out with a small space like a 10 foot x10 foot to begin with. But there are other ways to improve your isolation that can really be effective (though never as completely soundproof) that are quite a bit cheaper. All it takes are some construction tools and a little time, so here we go:

Step 1 - Add some mass to the walls and ceiling to increase your isolation. The least expensive way to do this is with 3/8” cement backing board. This is the same thing that’s used in showers and is sometimes called “Cement Board”. Home Depot sells 3 or 4 kinds and it does a great job for just a little bit of money. Plus, it doesn’t take up a lot of space and is way more efficient than regular drywall. It usually comes in 5’ x 3’ panels, but they weigh about three times what a panel of 4’ x 8’ drywall weighs (and you want all that extra weight to increase the mass, and therefore, the isolation). Make sure that you both glue and screw the cement board to the existing wall, since anything that isn’t absolutely tight will either rattle or give the room an unwanted resonant ring later, and defeats the isolation (see Principle #2).

Acoustic Principle #2

Think of air like water.

Any space between any construction joint lets the air out (or in)

and acts the same as if the room was filled with water,

so the idea is to make sure that there are no air leaks.

Step 2 - Get the thickest solid oak door that you can afford, then make sure you get a doorjamb. The trick here is to make sure that there are no air spaces around the door, and you do this by applying weather stripping around it on both sides. Most commercial studios use a double door “airlock” with a door attached to each side of the wall to maximize the isolation. You might get by with just a single door as long as you eliminate all the air spaces around it (see Principle #2).

Step 3 - Glue and screw some strips of ¼” low grade inexpensive industrial plywood to the cement board, and then glue and screw ½” regular drywall on top of that. The drywall is there primarily so there’s an anchor to attach the wall treatment outlined in step 4 in a later post.

As you've noticed by now, these 3 steps just aren't possible in a lot of home recording situations, but they're the only way that you can ever hope to truly isolate yourself from your neighbors and them from you.