The Plane Wave Reciprocity Parameter and Its Application to the Calibration of Electroacoustic Transducers at Close Distances

The reciprocity parameter for a plane wave sound field is shown to be equal to 2A/ρc, where A is the area of the plane piston source and ρc the characteristic acoustic resistance of the medium. It is shown experimentally that the sound field in front of a plane piston source is effectively plane over a distance approximately equal to A/λ, and that in such a region the plane wave parameter may be used to obtain a free field calibration of the transducer by the reciprocity method.