Sound Power Measurement in Nonstandard Environments

Abstract

The measurement of the sound power produced by many types of apparatus is often desirable and sometimes necessary when neither an anechoic chamber nor a reverberation room is available. When measurements are made in an enclosure where the absorption of the walls may be arbitrary, some means of determining the effect of the enclosure upon the observed sound pressure level measurements is necessary. One possible means of attack has been suggested [R. J. Wells, “Power apparatus and systems,” Trans. Am. Inst. Elec. Engrs., No. 21, 1170 (December, 1955)]. An alternative method is presented here, having the significant advantage that no measurements need be made until after the apparatus whose sound power is to be measured has been installed in an enclosure having reasonably arbitrary absorption characteristics. The procedure requires the taking of two sets of sound pressure measurements—one set with the apparatus operating in the enclosure as normally constructed, and a second set after the sound absorbing properties of the enclosure have been modified by the introduction of acoustic material of appropriate area and absorption coefficient. From these data, the sound power output of the apparatus may be determined.