Performance evaluation of a three dimensional intensity probe

Abstract

A three dimensional intensity probe using four microphones is proposed. Four microphones are placed at apexes of a regular tetrahedron. One is placed in the front and three others consisting a vertical regular triangle are in the back. The microphones are attached at the tips of parallel thin tubes. The microphone arrangement is not the conventional face to face type. The aim of this type of microphone arrangement is to design a sound intensity probe with a simple structure, which is essential for reducing the diffraction problem. Algorithms for three dimensional intensity components from cross spectra are given as well as for leakage components. Measurements of sensitivity characteristics in an anechoic room using two types of probes with 60mm and 20mm microphone separations show that sensitivity fluctuations are small enough (less than 1dB) for the practical application of the sound intensity method. The leakage errors of approximately 5%(-13dB) seem also acceptable. The measurement results indicate that sensitivity and leakage errors will become smaller if a more ideal plane wave field in an anechoic room is achieved.