Howto Soundproof an Apartment
From the Wikipedia [http://en.wikipedia.org/wiki/Sound_transmission_class] article: > Sound Transmission Class (or STC) is an integer rating of how well a building partition attenuates airborne sound. Materials which can improve STCs in walls include mass-loaded vinyl (MLV), standard drywall, “soundproof” drywall (such as QuietRock, Supress,