OVERVIEW

Sound power level L _W expresses the amount of sound energy that is radiated by a given source, regardless of the space into which the source is placed. The sound pressure level L _P can be estimated if the absorption and volume of the room are known.

For example, a 30-hp electric motor is placed in a mechanical equipment room finished entirely in painted concrete. This bare reverberant cubical room is 10 by 10 by 10 ft. The sound power levels L _W listed in the table below were obtained by the manufacturer from laboratory tests conducted according to the provisions of ANSI S 1.35.

To find the reverberant sound pressure levels L _P from this motor in the mechanical room, first calculate the room absorption and reverberation time at octave-band center frequencies from 125 to 4000 Hz. Next, estimate the L _P ? L _W difference at 1000 ft ³ from the graph on the following page. Finally, the reverberant L _P equals L _W plus the L _P ? L _W difference.