A numerical and experimental investigation of the performance of sound intensity probes at high frequencies

The upper frequency limit of sound intensity probes with a certain microphone separation distance has generally been considered to be the frequency at which an ideal probe that does not disturb the sound field would exhibit an acceptable finite difference approximation error. However, a numerical investigation has indicated and an experimental investigation has confirmed that the resonance in front of the cavities of the microphones to some extent compensates for the finite difference error. A practical conclusion is that a probe with half-inch microphones separated by a 12-mm spacer performs very well in sound power determination up to 10 kHz, which is an octave above what has hitherto been considered to be the upper frequency limit of this configuration.
The investigation was initiated during Vicente Cutanda's stay at Department of Acoustic Technology in 1995. In 1996 the efforts have been concentrated on testing the validity of the numerical findings under a variety of sound field conditions.