ARI Standard 885 provides a method for calculating sound pressure levels in rooms below plenums containing air-handling devices. An important step in the calculation is the correction of the sound power for the device from values provided by the manufacturer to values appropriate for use in occupied spaces. This correction is called the "environmental adjustment factor." It compensates for the fact that sound power measured for a source placed outdoors or in a hemi-free field has been found to be greater at low frequencies than the sound power measured for the same source in a reverberation room. When making predictions of sound pressure level in a room using such sound power levels, one has to estimate the reduction in sound power caused by the room. Estimated reductions provided in ARI 885 were examined during ASHRAE research project RP-755 and found to be too large. Lower values are suggested in this paper.

Units: SI