Acoustic intensity measurement error for complex sources

Abstract

There has been much discussion in recent literature of the accuracy of the two-microphone method of acoustic intensity measurement. The errors introduced by the finite difference formulation for intensity have been a frequent topic of investigation. However, these treatments have been limited to ideal plane wave and point sources. This paper describes a study of finite difference approximation errors for more realistic, finite sized sources. Error expressions are developed for a pulsating sphere, an oscillating sphere, and a piston in an infinite baffle. For the spherical sources, the error expressions derived are identical to those of their ideal equivalents, the point monopole and dipole. In the case of the piston source, large errors are predicted for particular conditions. For nearfield measurements along the piston axis, intensity level measurement errors can approach infinity.