Output of a Sound Source in a Reverberation Chamber

Abstract

Expressions are given for the sound power output of a simple source as a function of position in a rectangular reverberation chamber. The method of images is used in the derivation. The power output of the source near a single plane reflecting wall equals P[1 + (sin 2kx)/2kx], where P is the free-field power output, x is the distance of the source from the wall, and k is 2π f/c; f is the frequency and c the sound velocity. Similar but more complicated expressions hold near corners and edges of the chamber. Thus a simple source with given volume velocity can emit either more or less sound energy in a reverberation chamber than in a free field. When the source distance from the wall exceeds about one wavelength, the power output closely approaches the free-field value. The reverberation chamber can be considered as presenting an impedance which varies with source position. Experimental data are given which support the theory. The reverberation chamber method of measuring the power output of sources is considered in the light of these results. In the general case of an extended source emitting nonspherical waves near reflecting surfaces, the power output cannot be predicted in terms of the free-field output. It has to be measured experimentally.