System for the measurement of acoustic energy density

Abstract

In the reverberation chamber method of measuring the sound power radiated from an acoustic noise source, pressure microphones are used in arrays, traversed over fixed paths or used singly with a rotating diffuser. The purpose is to accurately measure the potential energy density in the sound field produced by the noise source. In general, accuracy is limited by the variance in the measurement of the potential energy density. When the total energy density (potential and kinetic) is measured, the variance should be cut in half. A system has been designed and built that measures the total energy density in a three‐dimensional sound field. Three sets of spaced pressure microphones are placed orthogonally. For a set the signals are averaged and squared to produce the potential energy at a point and the difference signal is squared to give the square of one component of the acoustic velocity vector. By multiplexing the sum of the squares of the three components of the velocity vector the kinetic energy is produced. The three pressure squared signals are averaged to produce the potential energy, halved and added to half the kinetic energy to give total energy density. Calibration is accomplished with an acoustic calibrator or pistonphone and small plane wave tube. Measurements made in one dimensional and three dimensional sound fields will be presented.