Sound from HVAC ducts or devices in ceiling plenums passes through the ceiling system to the room below and can cause annoyance to the occupants of the rooms. ARI Standard 885 provides a method to calculate the level of the sound in the room using the sound power of the device and some attenuation factors for the ceiling. The goal of ASHRAE research project RP-755 was to evaluate and extend the information given in ARI 885. This paper describes the attenuation factors found for six types of ceiling tiles and four air-terminal units. Attenuations at low frequencies were found to correlate with the area of the lower face of the device emitting sound. Sound fields in the room below were essentially uniform; no significant attenuation with distance was found.

Units: Dual