Free Field Calibration of Microphones

Abstract

THE determination of the ‘field calibration‘of a microphone, that is, the sensitivity under free space conditions, has been rendered difficult in the past by the presence of air currents comparable with the velocities to be measured, or field irregularities and uncertainties in direction due to reflection from the walls in a small enclosure. If, in the case of a pressure operated microphone, one tries to avoid this trouble by determining the pressure calibration by the resonant tube¹ or thermophone methods and by calculating the increase in sensitivity due to reflection from the microphone, the difficulty, if not impossibility, of making this calculation rigidly for practical forms of microphone is encountered.