Acoustical impedance measurement.

Abstract

Many components of specialty transducers have extremely tight acoustic impedance tolerances and become difficult to measure in a production environment. Comparing the device to the acoustical impedance of a cavity is one method of determining its acoustical impedance. A precise method of determining the acoustical impedance is described. The technique applies methods normally found in defining cavities for pressure reciprocity calibration to obtain a precision acoustical reference. Pressure reciprocity standards also define how environmental factors influence acoustical properties and these are included into the system to maintain the precision regardless of the environmental conditions or the frequency of operation. Further improvements are obtained by employing differential measurements throughout the measurement and calibration process to eliminate many common errors common to field calibration of microphones. Ultimately the measured data are curve fitted to an equivalent circuit model to extract the desired components from the measurement artifacts. This talk will discuss the method of defining the acoustical components and extracting the desired value from the equivalent circuit model.