Elimination of the Phase Mismatch Error in PP Probe Using Synchronous Measurement Technique

Abstract

The paper presents a modification of the pressure-pressure (PP) sound intensity measurement method. In the proposed solution simultaneous measurement with a pair of microphones (used in the classical PP probe) is replaced by a sequence of measurements taken with a single microphone placed in successive positions. This approach requires an additional (reference) microphone to synchronize the successive measurements. Although, in the process of calculating the sound intensity only the signal from the measurement microphone is used. Thanks of this the errors associated with differences in the frequency responses of the measurement microphones (especially phase mismatch error) that occurs in the classical PP method are eliminated. This approach simultaneously increases the random error and limits the measurements to periodic signals only. The article presents the principle of operation of the classical PP probe and the currently used methods of phase mismatch error elimination based on pre-calibration of the probe. Next, the theoretical basis of the proposed measurement method is described. To verify the effectiveness of phase mismatch error elimination in the proposed method, an experiment was conducted. It consisted in estimation the angle of incidence of an acoustic wave under controlled conditions in an anechoic chamber. The measurement was carried out with the classical PP probe and with the modified method. Measurements were made for different sound sources (a loudspeaker set and a small electrical device). In the final part of the paper, the results are discussed, both methods (classical and modified) are compared and potential applications of the proposed method are indicated.

Design of a Phase Calibrator to Evaluate Non-Matched Microphones for Intensity Probes

“…Given the theoretical background, it is clear that before proceeding with the sound intensity measurement, it is necessary to address any intrinsic phase mismatch between the microphones [10][11][12]. With "intrinsic", we refer to the phase mismatch that the two microphones carry as a bias error and therefore is not linked to the pressure difference generated by the measurement itself.…”