Errors in the automatic measurement of spatial acoustic intensity in the direction of sound energy propagation with a rotating probe

Abstract

For the automatic measurement of spatial acoustic intensity the authors have devised a rotating probe comprising two microphones, which are arranged in parallel with the axis of the probe's holder and shifted by a minute distance from each other in the direction of the microphone axis. If measurements are carried out, once before any rotation of the probe, and twice at two different predetermined angles of its rotation around the holder axis, then it is possible to determine easily the three components of an acoustic intensity vector in the corresponding three co-ordinate axis directions. Theoretical and experimental investigations are presented of the possible error in automatic measurement of spatial acoustic intensity in the direction of sound energy propagation with such a probe. On the basis of the theory of measurement with a rotating probe and the fundamental error theory of the acoustic intensity method, it is possible to calculate the theoretical error in the direction of sound energy propagation. The results of calculations of this error agree well with those of measurements, and it is shown that the measurement error in the direction of sound energy propagation depends upon the frequency of the sound wave as well as on the incidence angle on the probe. These results have made it possible to determine the measurement error limit in the direction of sound energy propagation.