Free-Field Reciprocity Calibration of Capacitor Microphones at Frequencies from 19.95 kHz to 316.2 Hz

The free-field calibration of a group of three one-inch capacitor microphones has been carried out over a frequency band extending from 19.95 kHz down to 316.2 Hz using the reciprocity method recommended by the IEC in Publication 486 (1974). The bridge method used for the electrical measurement gives information about both magnitude and phase; in magnitude, the results generally fall within ± 0.1 dB of their mean values. A companion paper considers the correlation of the free-field results with those from low-frequency coupler measurements and with results obtained using an electrostatic actuator.