Uncertainties in realising the standard of sound pressure by the closed coupler reciprocity technique

Sources of uncertainty associated with realizing the standard of sound pressure using one-inch laboratory standard microphones calibrated by the closed coupler reprocity technique are discussed. A measurement technique designed to achieve an unacceptable level of uncertainty is described and the components of systematic and random uncertainities in the range 63 Hz to 12.5 kHz are given. With suitable microphones, the overall systematic uncertainty of calibration is estimates to be less than 0.025 dB at frequencies up to 1 kHz, increasing to 0.11 dB at 10 kHz.