A sound intensity probe for measuring from 50 Hz to 10 kHz

The upper frequency limit of a p-p sound intensity probe with a certain microphone separation distance is generally considered to be the frequency at which an ideal p-p probe with the same separation distance would exhibit an acceptably small finite difference error in a plane wave of axial incidence.

It is shown in this paper that the resonances of the cavities in front of the microphones in the usual 'face-to-face' configuration give rise to a pressure increase that to some extent compensates for the finite difference error. Thus the operational frequency range of the intensity probe can be extended to an octave above the limit determined by the finite difference error if the length of the spacer between the microphones equals the diameter.