Abstract:
The accuracy of microphone reciprocity pressure calibrations deteriorates due to environmental noise at relatively low frequencies. A computer-controlled automated system that has the potential to reduce calibration uncertainty at low frequencies has been developed. The reciprocity calibration apparatus was placed on a rigid platform with conventional rubber vibration isolators. A lock-in amplifier was employed to assist data acquisition and correlation, with an auxiliary microphone placed near the reciprocity calibration apparatus to measure environmental noise. Calibration results were continuously logged for various environmental conditions during a test period of 2 weeks. Measurements confirmed that the noise signal received by the auxiliary microphone is highly correlated to that of the calibration system, and that adaptive noise-canceling techniques can be used to reduce calibration uncertainties. Preliminary results obtained are encouraging.