Technical issues related to sound power measurement standards

Abstract

As the ‘‘3740 series’’ of International Standards on Sound Power Determination are revised, several technical issues must be considered. In ISO 3745, the characteristics of the sound source used to qualify a hemi-anechoic room for precision measurements must be carefully considered. The use of a low-profile source placed just above the floor of the room, and the performance of the same source in the plane of the floor are described. The discrete microphone positions used on a hemispherical measurement surface must also be carefully studied and perhaps changed. Experience with ISO 6926 shows that an array of microphones having discrete positions have ‘‘holes’’ in their frequency response, and optimization of this response is critical. In ISO 3741, the method used to determine the minimum distance between the source and the microphones must be carefully studied, especially at high frequencies. The qualification procedure for reverberation rooms in ISO 3742 must also be examined with a view toward the use of modern instrumentation and speed of performing room qualification. The use of special test signals matched to the characteristics of a particular analyzer is considered.