A soundproof room is a specially constructed space in which almost all generated noise cannot escape. Recording studios routinely employ these rooms to minimize external noises and isolate individual instruments or voices. Research engineers may also utilize a soundproof room to measure the audible output of a machine. Apartment dwellers and homeowners often create these rooms to minimize the sounds of entertainment systems.
Creating a room that is truly soundproof is not easy. To understand the difficulty, a crash course in acoustics may help. Amplifiers and speakers generate soundwaves, which must travel through some sympathetic medium in order to reach the ears of the listener. In a typical room, air is that medium. Sound energy travels through air until it strikes a surface such as a wall, but a single non-insulate wall does not prevent all sound waves from penetrating into the surrounding area. It may prevent higher frequencies from leaving, but low frequencies continue through the wall and into the air again. This is why a neighbor's loud stereo may sound like a bass and drum solo in your apartment.
An ideal room that is soundproof would eliminate all possible methods for soundwaves to travel, but this would include the air you'd breathe. In lieu of a total vacuum, the next best solution is dampening, or absorbing, the soundwaves as much as possible. A soundproof room is really a room within a room. There are two walls separated by a void filled with thick insulating material. The wall studs are offset so there is no physical connection between them. Soundwaves which penetrate the inner wall of the room must first travel through the sound-absorbent insulation and then through a second wall barrier. This eliminates most, but not all, of the troublesome noises.
In a professional recording studio, the room may actually be lined with lead sheets for maximum sound absorption. This would be too expensive for the average homeowner, but less expensive soundproofing materials are available. Most work on the principle of dampening or deflecting soundwaves. Foam panels with vertical and horizontal slats can be placed on the inner wall of a soundproof room to deflect soundwaves away from the outside wall. Doors in this room are also designed to be sound dampening. The door alone in a professional recording studio can cost thousands of dollars.
Many soundproof room designs do not incorporate windows, but it's not impossible to install a soundproof window system. Glass is an excellent carrier of soundwaves, but a double or triple pane system can dampen vibrations before they escape into the outside air. If the air is removed between panes and the frame is installed properly, a window can be soundproofed effectively. For even more sound dampening, special curtains constructed from heavy materials can be hung over windows.
The floors and ceilings of a soundproof room must also be insulated with sound-dampening materials. A solid concrete floor is usually best for minimizing soundwaves, but some designers suggest a 'floating' floor plan, in which the subflooring is covered with a Neoprene-based insulating material and the floor essentially floats above it. The ceiling can be amended with a suspended grid of acoustic tiles and additional insulation blown into the void.
Having a virtually soundproof room can solve many more problems than it creates. Musicians can play louder instruments without fear of disturbing the peace, while owners of entertainment systems can use them at any volume.