THE INFLUENCE OF MICROPHONE VENTS ON THE PERFORMANCE OF SOUND INTENSITY PROBES

This paper examines the influence of the pressure equalisation vents o f conventional condenser microphones on the performance of sound inten sity probes provided with such microphones. It is shown theoretically and demonstrated experimentally that the vent systems give rise to a b ias error that is proportional to the reactive sound intensity. A disc ussion of this source of error is presented, it is concluded that, alt hough the error can be very large at low frequencies under some condit ions, this source of error is nevertheless relatively harmless since i t will usually be possible to avoid such conditions. The error is alto gether eliminated if one uses 'single port' microphones, that is, pres sure microphones with particularly low vent sensitivity.