The first thing to realize when you're thinking about in-home acoustics is that minimizing sound and sound-proofing are not the same. In fact, when people talk about sound-proofing a room, what they're usually referring to is sound-deadening. It is much easier to construct or modify a room to deaden sound than it is to make it totally sound-proof. Sound-proofing is a whole different process — a complicated and difficult structural result to achieve — and it's rarely done in the course of ordinary house-building. As you might guess, sound-proofing a space can also be very expensive to do. It involves building a system of double walls where virtually nothing within one wall is allowed to touch anything in the other wall — a sort of room within a room. Sound travels in waves of vibration, and any vibration will transfer from one side of a wall to the other through anything that touches, including insulation. So truly sound-proofing an area such that no sound at all can escape is beyond the scope of most home renovation projects. Realistically, what the average homeowner wants is to deaden sound. Based on the same general principles, there are a few different techniques you can use to do this, and they can be combined to achieve greater levels of quiet. It really becomes a question of how far you want to go to control the acoustics of the space you're dealing with, but using fairly conventional building methods you should be able to contain sound within a room to a satisfactory degree.
First off, if you want to sound-deaden a room and don't have any space to sacrifice, there is sound-deadening insulation that can go into the wall. You can then cover the wall with a sound-deadening product such as homasote. There's also a product available now that actually is a sound board designed especially for the purpose. That wall then gets covered again with a layer of 5/8-inch drywall. If you have floor space to spare, you can take the room's sound-tightness to another level by spacing the wall with another layer of drywall, to create what is called a "resilient channel" behind the room's finished walls — the room-within-a-room concept. A saw cut in the floor, up the wall, and into the ceiling between the two walls of the channel will further enhance the room's sound-tightness by preventing vibrations from transmitting through the floor and ceiling into the floors and ceilings of adjoining rooms. You should then cover that wall with yet another layer of drywall. While not as silent as more expensive sound-proofing processes, it works on the same principle of creating gaps that make it harder for vibrations to move along. The media room in the Milton house offers a good example of how sound-deadening techniques can be combined. The insulation that we used is a liquid, which we applied both in the walls and the ceiling. The product is an open-cell material that dries and cures in six seconds and has very good sound-dampening properties. The walls were then built with double layers of drywall in such a way that none of the seams of the drywall lined up with the seams of the layer below it. The bookcases on each end were spaced away from the wall so that the vibration in the bookcases don't touch the wall in back. The ceiling was also built to hang in suspension from the structure above, and again, using double layers of drywall. Finally, Vinnie Ferrara, a wall-covering specialist, covered the walls in the media room with liner and fabric panels. First, Vinnie applied vibration-absorbent polyester fill to the walls with staples, leaving a 1-inch border around the perimeter. Over the polyester he stapled panels of silk fabric — a material that is both attractive and extremely durable as a wall-covering. Vinnie then used hot glue to apply a matching fabric trim that finishes the look and hides the staples. This is also a good method for achieving some sound-dampening in a room that is not being rebuilt, because the fill and fabric can be easily applied to existing walls.
As I said earlier, the main principle at play is simply that, wherever possible, you try to prevent sound waves from traveling into and out of the space through the air and surrounding structure. Therefore, as an example of what definitely doesn't work, tightly packed fiberglass insulation in your walls won't help deaden sound. Such insulation only serves to make your entire structure more solid, enabling — not preventing — the transference of vibrations. So whether you're looking for a place to hide your kids with their drum sets and video games, or a place where you can hide from them, listen up: vibration limitation is the key. Rob those waves of all their best escape routes and you should be well on your way to some peace and quiet.