|Keeping the Sound in the Room: Soundproofing|
|Home Theater Feature Articles Audio Related Articles|
|Written by Dick Ward|
|Monday, 13 December 2010|
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Whether you've got a dedicated theater space or a multi-purpose room that you use for your home theater, there is a wide array of options available to you, ranging from the cheap and simple to the costly and complex. To know how to block the sound that's escaping your room, it's important to know just how it's getting out in the first place. There are two possible ways for sound to get out, and more often than not you're getting a mixture of both.
The first way - airborne - is the simplest, both to think about and to fix. Sound waves travel through the air to reach our ears inside our listening room, so why should it be any different outside of it? Windows, vents and walls can all be escape avenues for sound waves. To stop airborne sound, you simply need to put something in front of it. It's not the size that matters, but the mass and therefore the density. It makes sense of course; a sheet of lead will stop sound better than a sheet of paper.
The second way sound is getting out of your home theater is through solid objects like the floor. Like airborne sound, structure-borne sound can travel through your walls and ceiling as well, but through different avenues. The waves travel through the object itself. Structure-borne sound requires separation. If two objects aren't touching, the sound can't get through. It's not the most complicated concept, but executing a fix can be difficult, especially if the object your audio is travelling through is the floor.
In order to conquer the task of soundproofing your home theater, you'll need to be able to defeat both airborne and structure-born sound. The combination of these two requires a dual pronged approach. It requires massive objects to block the airborne sound and separation of those objects to prevent structure-born. If you've lived in a less than spectacular apartment or an old house, you've experienced the dreaded paper-thin wall that allows sound to travel wherever it pleases. The walls inside of your home are likely superior to these, but they could be better.
You'll notice the most immediate improvement to the audio isolation of your home theater by fixing up your walls. This is where people building from scratch get lucky. There's no need to tear down walls and you won't have to worry about losing a little bit of space in your room. Most people with drywall have a standard setup that consists of sheetrock on either side of the wall, insulation in between and a single stud that both pieces attach to. As you might imagine, this isn't the best solution. Just two pieces of sheetrock and a bit of insulation in between isn't going to do much to stop that airborne sound. To add to the trouble, using a single stud means those structure-based vibrations can travel right through the wall into the next room.
A step up from the standard is the staggered stud technique. Instead of using the same stud, a staggered stud drywall setup utilizes separate studs for each side of the wall. It requires a slightly wider wall, but the additional insulation and separation of the sides makes for a much more sound-proof construction. For maximum sound isolation, you'll want to add something special into the mix as well. You can go with either soundboard or a product like Green Glue that's made specifically to keep sound from travelling through the walls. Either way, you'll be adding mass to keep the airborne sound from getting out.
You can also decouple the drywall from the framing using resilient channels - metal strips that move the drywall an extra half inch away and add an extra bit of sound isolation. Some experts warn against these though, as they have potential to create extreme amounts of resonance at specific frequencies. That's definitely not something you want while enjoying a movie. Once your walls are set there's another big surface you'll want to take a look at - the ceiling. Ceilings can be very similar to walls if you're going with the drywall approach, but there's more you'll want to take into consideration.
The thing about ceilings - the definitive thing about ceilings - is that they're attached to the floor above them. It's not as big a deal if there's nothing above you, but if you've got a basement viewing room or a home theater with a bedroom about it, keeping sound from going out through the ceiling will be essential. There are several methods for isolating the ceiling including suspending it from specialized spring hangers, or using resilient channels to decouple the ceiling from the floor above. Whatever method you use, separation is key to avoid both sound going out and sound coming in. Typical drop ceilings don't do much to keep the sound isolated, but with proper soundproofing it can work. If you've already got a grid installed, for example, you can pick up special tiles, thicker and denser than those commonly used, and with much stronger sound absorption qualities.