The crash of a cymbal, the clang of a bell...all physical actions send “sound waves” rippling through the air. When these “waves” reach our ears, they vibrate a sensitive membrane—the eardrum—and we hear them as sounds.

Noise is simply unwanted sound. In the home, most people consider noise to be just about any sounds other than those made by what they’re doing. For example, if you’re on the phone, you don’t want to hear the television in the next room. Conversely, if you’re watching television, you don’t want to hear phone conversations. And you probably don’t want to hear your teenagers’ music, period.

Unfortunately, most walls and ceilings are only marginally effective at blocking noise. They are built like drums. They have membranes—typically drywall—on both surfaces, fastened to solid structural members and separated by a cavity of air. Sound waves strike one surface and carry through the structure and the air to the other surface, where they’re broadcast as audible noise.