Phase response measurement with the three-port two-microphone coupler

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With the advent of sound intensity measurement, the need for a reliable and precise method for the assessment of phase response of microphones is evident. For national laboratories, a direct method is preferred. There are less time-consuming signal-processing techniques that are capable of measuring the phase response of microphones. However, for high-precision measurement, it is relatively difficult for national laboratories to verify or to substantiate the uncertainty of phase measuring techniques that involve inaccesible computational algorithms. The theory on precision phase measurement with the three-port two-microphone coupler [J. Acoust. Soc. Am. 71, 1276–1277 (1982)] is presented with experimental verification. The uncertainty of the method depends on the uncertainty of the phase measuring instrument. With a calibrated commercial phase meter, the uncertainty is typically 0.02 deg.