Diffraction constants for pressure gradient transducers

Conventionally the diffraction constant D of a receiving transducer (microphone or hydrophone) is defined as the ratio of the average sound pressure acting on the blocked diaphragm to the free‐field sound pressure. This definition is inadequate for transducers that have complex vibration patterns, and, in the absence of ad hoc modifications, it will fail to give the correct results for pressure gradient transducers. A new definition based on the general theory of transducers with fixed velocity distributions is therefore introduced. The diffraction constant is assigned not only the function of accounting for scattered wave effects but also the function of extracting from the surface pressure distribution the component that drives the velocity distribution (or vibration pattern) of the transducer. The diffraction constant depends on the choice of the reference velocity that is associated with the acoustic port of the transducer. A spatial rms reference velocity is defined, and it is shown to be a suitable ...