One-microphone sound intensity method

Abstract

The two-microphone sound intensity method is potentially a valuable tool for noise source identification, sound power determination, and for other measurements (e.g., transmission loss) that are based on sound intensity measurements. An essential ingredient in an accurate sound intensity measurement is the accurate measurement of the phase between the two microphones. Because the phase is generally small, on the order of a few degrees, the microphones must either be "phase matched," or a phase calibration procedure must be used. This paper outlines the design and test procedures for using a plane-wave tube to perform a microphone phase calibration with an uncertainty of less than approximately 0.2 deg. The phase calibration procedure is illustrated for a pair of condenser microphones and for a pair of miniature crystal microphones typically used in hearing aids.10:05 S103

The Two-Microphone Sound Intensity Probe

“…Rearranging equation (2) to solve for pressure in terms of velocity, it is evident that a two-sensor probe need not use pressure-sensing microphones [10]. Using the pressure/gradient approach, approximations of higher order and involving additional microphones can be substituted for equations (3) [11,12]. Still another approach is to use Helmholtz integral or holography techniques with multi-microphone arrays [13,14].…”

“…Still another approach is to use Helmholtz integral or holography techniques with multi-microphone arrays [13,14]. If the sound field is deterministic, or is sufficiently stationary, single-microphone techniques can be appropriate [12][13][14][15][16].…”

“…As a practical matter, the experimenter usually does not have the required L p , but only the two measured sound pressure levels. Provided that these do not differ too much, either one or their mean can be used in equation (12) [21]. Note also that L^i 0 is a property of the probe that usually needs be measured only once.…”