Reciprocity Calibrations in Closed Couplers

The responses which are customarily defined for a transducer operating in a closed coupler do not lead to a reciprocity parameter which is independent of the acoustic impedance of the transducer unless the impedance is high compared to the impedance of the cavity. If the response of a reversible transducer used as a sound source is defined as S = pb/I, where pb is the pressure produced in the cavity for a current I into the transducer, and if the response as a microphone is defined as M = e/pg, where e is the open circuit voltage and pg is the pressure produced by a source of constant volume velocity applied to the cavity prior to the introduction of the microphone; then a reciprocity parameter may be obtained which is independent of the acoustic impedance of the transducer and the response of a microphone having a low acoustic impedance can be determined by a reciprocity calibration.