Effect of Absorption and Rotating Vanes on Qualification Procedure of Reverberation Chamber

Abstract

The new ANSI Standard 1.2-1972, “Methods for the Determination of Sound-Power Levels of Small Sources in Reverberation Rooms,” and ASHRAE 36–72, “Methods of Testing for Sound Heating, Refrigerating and Air-Conditioning Equipment,” define criteria for the reverberation chamber which have to be satisfied in order to qualify for the measurements of sound power at discrete frequencies. As it has been found by measurements of existing reverberation chambers with no additional treatment, the criteria for measurements of sound power with only one source position are not satisfied. However, when applying absorption and rotating vanes, it is possible to achieve the qualification. At low frequencies the addition of absorption is substantial. The rotating vanes are very useful at middle and high frequencies where the increased absorption must be avoided. The effect of absorption can be explained by its influence on modal overlap. The rotating vanes modulate the sound field. This paper presents practical data on qualification procedure.