The cylindrical microphone array: A proposal for use in international standards on sound power level measurement

Abstract

To determine the sound power level of a stationary noise source, a hypothetical measurement surface is defined which envelops the source under test. The sound pressure level is measured at selected microphone positions on this measurement surface, and the sound power level computed. A previous paper [M. A. Nobile and J. A. Shaw, Inter-Noise 99, 1535–1540] introduced the concepts of the cylindrical microphone array and cylindrical measurement surface and presented results from initial measurements. The array was suggested as a more practical alternative to the current parallelepiped or hemispherical arrays for measuring the sound power level of sound sources in hemi-anechoic chambers according to standards such as ISO 3744, or the Information Technology and Telecommunications industry test code ISO 7779. It was also suggested that for certain types of machines, such as tall, rectangular computer frames, or other equipment with similar aspect ratios, the cylindrical measurement surface may yield results that are more accurate. In this paper, the results of further experiments and measurements using the cylindrical array will be presented, along with a proposal for incorporating this new array into the international standards on sound power level measurements.