Determination of laboratory standard microphone parameters in reciprocity calibration

Abstract

Reciprocity calibration is one of the most accurate technique to calibrate a primary standard condenser microphone. The calibration procedure is conducted according to IEC 61094-2:2009, including the calculation of acoustical transfer impedance, electrical impedance as well as correction of thermal conduction, radial wave-motion, and ambient pressure temperature. This paper investigates four characteristics of laboratory standard microphone in reciprocity calibration, front cavity depth, equivalent volume, resonance frequency, loss factor, and their influence on the pressure sensitivity level. In order to obtain more accurate calibration results, microphone parameters should be determined for every single laboratory standard microphone, instead of using nominal values provided by the manufacturer in the reciprocity calibration system. Several laboratory methods for every single microphone characteristic are analyzed and the optimal solution is decided based on applicability, time cost, and accuracy evaluation.