How to Control Sound Transmission Through Floors Reducing sound transmission through floors and ceilings is much more difficult than controlling sound on the same level. The builder faces all the problems of airborne-sound control, plus the problem of structure-borne impact noise. The expression "waiting for the other shoe to drop" must have been coined by an apartment dweller in a building with poor floor construction. How Much Isolation Do We Need? A building component's ability to resist sound transmission is rated by Sound Transmission Class. (For a full explanation of STC, see "The ABCs of STC Ratings," page 32.) For instance, a floor-ceiling system with an STC of 35 could reduce a noise level of 75 decibels (inside a moving car with
