The first method is the simplest. Just pour 18” of concrete on the floor, walls, and ceiling. Make sure the room is completely surrounded with very thick concrete and sound will have a hard time getting out. Of course, this is very expensive. If you have a leak, you are done! If there is a place where sound can get through, it will. It's kind of like winterizing a home with insulation. One little hole will allow a lot of cold air through! This method of soundproofing usually isn't a possibility for a home recording studio.

In a slightly more realistic fashion, I've heard of some people having great results by simply adding mass to their current rooms. So by adding a second layer of drywall, it's possible that you will reduce the amount of of acoustical energy leaving the room. Obviously, this is cheaper and a little more realistic than pouring energy concrete to stop a nuclear blast.

Room Within A Room

Method two is what is called a Room Within A Room. Basically, you take an existing room and build another room inside it leaving a 3” air gap or so. It's extremely important that this new room not touch the old room in anyway. In fact, you don't want the new wall to be mechanically connected to the floor , ceiling, or any other part of the original structure.

The concept here is that the acoustical energy coming of a kick drum, for example, will quickly fly through the air. As soon as it hits a wall, it's going to try to go through it. Well, in order to do this, it has change. Obviously, it has to use energy to shake the wall. Then it will go through the drywall, studs, etc of the wall and come out the other side. When it comes out the other side, it has less energy than it did before the wall.

So, by adding a second “conversion” you can greatly reduce the amplitude of a sound going out into the real world. The downside is if any part of your new room (including the floor) is mechanically connected, the sound will flow through the floor to all over the building. This is called “transmission”. So it's extremely important that a soundproofed room be mechanically isolated when using the Room Within A Room concept.