? Acoustics and Sound
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Perfect your home theater's acoustics with these how-to guides

The acoustics of a home theater are one of the most overlooked topics by do-it-yourselfers. Most people get so caught up with the how their theater will finally look like, that they neglect to put in the time to properly address potentially serious acoustic issues.

Go big or go home

One of the neat things about home theaters is the ability to have big sound. Cranking up the volume during the opening battle in Master and Commander really pulls you into the action. The problem is, you don't want to disturb other people in your home.

This is where acoustics come in. Sound is like waves of energy that travel through the air. When those waves hit an object, that object will start to vibrate. Anything touching that object will also start to vibrate and so on and so on until the energy is dissipated. Sound waves love to leak through cracks and gaps in floors, walls, electrical outlets, door jams, and ventilation ducts. This makes sound really difficult to control.

Good vibrations

There are many techniques you can use to help reduce the amount of sound that escapes your home theater. Some are expensive and some are cheap. Two main ways to reduce the transmission of sound are mass, and air. A 2 foot-thick cement wall is very effective at blocking sound because those waves would have to vibrate all that mass. You're likely not going to want to surround your new media room with such thick walls, so there's got to be a better way.

If you can't stop sound vibrations using brute strength, why not prevent the sound from traveling at all. When sound in one room comes into contact with a wall, it has to vibrate that wall. The vibrating wall then causes the air on the other side to vibrate as well, but some of the sound energy has weakened so the sound you hear isn't as loud. This is why a stereo in one room doesn't sound as loud in another.

We can use this to actually build a room within a room, a technique used by many professional recording studios. You'd basically build an extra set of walls and a new ceiling so there's literally a 6 inch gap of air surrounding the room. That gap of air and the second set of walls would eat up a lot of the sound wave's energy and you'll end up with a very quiet solution.

Staggering the studs within a wall can also reduce the amount of sound thats transmitted from one room to another. Filling the space between the studs with fiberglass insulation will further help soundproof the wall. The idea here is to prevent the vibrating drywall and studs on the inside of the room from vibrating the studs and drywall on the other side of the room. This is pretty effective and a good do-it-yourself solution.

Standing waves: The not so silent killer

The dimensions of a room can make or break the acoustic experience you can expect to get out of it. The distance the walls are from one another will affect how sound is reflected inside the room and create unwanted sound waves. These unwanted sound waves are known as standing waves. Since sound can reflect off of walls and other objects inside a room, there are places where sounds can cancel each other out, or actually reinforce the sounds you hear.

You can demonstrate this yourself by standing about 6 feet from a wall and clap your hands (the harder the better). Then take a step forward and listen. Keep clapping as you take more steps forward until you hear a change in the clapping sound. These standing waves will affect how people will hear a movie depending on where they sit in the room.

Special wall treatments you hang on your wall and even on your ceiling can help diffuse or absorb standing waves. These can easily be made and don't have to be ugly if you use your imagination. Wall treatments like these can help offset an unusually shaped room. Bass traps are boxes specially designed to absorb low frequencies. Bass can also reflect off walls and can create areas in your room where the bass is extra heavy, usually in corners. Placing bass traps in these locations will help eliminate these low frequency standing waves.

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