On the Reciprocity Free‐Field Calibration of Microphones Available to Purchase

The physical conditions for a valid reciprocity free‐field calibration are examined in considerable detail. The expression for the absolute value of the reciprocity parameter J is derived in a general manner. The result shows that J is actually a transfer admittance relating the volume current Q of the linear, reversible transducer to the pressure P this unit causes at a certain point in space. The usefulness of this concept in other than free‐field conditions is pointed out. The formula for the sensitivity of the unknown microphone is derived by a method which emphasizes the significance of the physical arrangement, and the limiting conditions are stated. Practical methods for determining the validity of the calibration are suggested.