CH-89-03-4 -- Low Frequency Problems in the Determination and Application of Equipment Sound Power Ratings PDF

There is a growing concern with low-frequency noise in buildings. Sound poweratings for the sources involved, however, typically do not include any data below the 125 Hz octave band because the present series of ANSI standards ($1.30-$1.35) and their ISO counterparts for the determination of sound power, while not setting any low-frequency limits, do not provide any information on measurement uncertainties for frequencies below the 125 Hz octave band. In reverberation room measurements, there are at least two types of Iow-frequency problems: (1) difficulties in obtaining a valid space average the sound pressure and (2) effects of the acoustic impedance seen by the source on its sound power output. The published literature on the second type contains conflicting information. This issue is important not only for standardizing equipment sound measurement and rating procedures, but also for the proper application of equipment sound power ratings in the design of quiet airconditioning systems.