Improved Formulation of the Acoustic Tr ansfer Admittance of Cylindrical Cavities

Summary The reciprocity calibration method using cylindrical cavities (called plane wave couplers )d escribed in standards assumes that only plane wave-motion exists inside the cavity ,w hereas radial wave-motion also exists. Ap revious investigation, which accounts for the radial wave-motion, analysed the acoustic field in cylindrical cavities, providing ac orrection to the plane wave theory quoted in the current IEC standard 61094-2 (1992 )a nd pointing out its relevance in the calibration uncertainties. The author expresses the acoustic field excited by the transmitting microphone (set at one end of the cavity )a sas um ove rt he eigenmodes of the cavity which satisfy Neumann boundary conditions and give sap rominent role to the shape of the diaphragm of this transmitting microphone. But in this analytical formulation, the influence of the finite acoustic impedance of the receiving microphone (closing the end of the cavity )o nt he shape of the acoustic pressure field inside the cavity is neglected. This limitation is pointed out in the present paper: the cavity boundaries need not be so highly idealised, in order to obtain am ore realistic representation of the acoustic field inside the cylindrical cavity and thus ad eeper accurac y in microphone calibration results.