Transmission of sound through suspended ceilings from HVAC terminal units

Abstract

An ASHRAE project to investigate factors determining the sound pressure levels in rooms below ceilings concealing air-terminal units has been completed. Four terminal units installed close to the six ceiling types used were the major noise sources. They were supplemented by two simulators powered by loudspeakers. Sound power was measured for each device in the 156 cubic meter test room in its reverberant condition. The levels in the room were measured for each combination of source and ceiling tile. Sound pressure level was measured as a function of distance from two sources in the room below. The main intent of the project was to validate ARI Standard 885 which provides a calculation method for such situations. Differences among ceiling types were less than expected; leakage around the edges of each panel is a dominant transmission path. Ceiling attenuations at low frequencies were found to depend on the area of the lower face of the units. Sound levels in the room were essentially uniform when the source was above the ceiling. The decay of sound with distance from the sources below the ceiling was found to depend on the inverse of the room reverberation time.