Experimental determination of the difference between diffuse and pressure field sensitivities of half-inch laboratory standard microphones

Frequently, is important to assure high accuracy to a measurement result then, a practical way to do that is calibrating the measurement instrument. Traditionally, a calibration can be performed by a comparison or an absolute method and the choice depend on the desired measurement uncertainty. In acoustics, absolute calibration of measurement microphone's sensitivity is usually performed by the reciprocity technique in three standardized sound fields: free, diffuse and pressure. Depend on the sound field, microphone's sensitivity will be different at high frequencies because the interaction between microphone and sound wave. While reciprocity in pressure field is performed by many institutes, in free-field, it is performed by a small number, and in diffuse-field, only by a very few. Institutes that do not perform free-field or diffuse-field calibration, commonly use a correction applied to the pressure field sensitivity to obtain the free-field or diffuse-field sensitivity. In this paper, diffuse and pressure field reciprocity calibrations are summarized and a correction to the pressure field sensitivity to obtain the diffuse-field sensitivity is presented. That correction, which is determined from reciprocity calibrations in the range from 1.25 to 16 kHz for half-inch laboratory standard microphones, is compared with standardized values.