Sensitivity correction method for a three-dimensional sound intensity probe

The upper frequency limit of a p-p type sound intensity probe is mostly determined by the sensitivity reduction of the probe. The sensitivity reduction is caused by obtaining the pressure from the average of the two pressure signals including the phase, and by obtaining the particle velocity from the finite difference of the two pressure signals. This is a systematic error suggesting a possibility of correction. In order to compensate or correct the sensitivity reduction, the direction of energy flow must be known. If a one-dimensional intensity probe is used, the probe direction must be varied to find the direction of the energy flow. If a three-dimensional intensity probe is used, the direction of the energy flow can be at least roughly estimated from a single measurement and then the sensitivity reduction can be corrected. This paper proposes a method of sensitivity reduction correction in the high frequency region for a three-dimensional (3-D) intensity probe. A theory of the method is described first and then numerical results that validate the theory will be given. This method works even for a probe with some amount of phase mismatch among microphones and for a sound field with reflections.