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Abstract
Objective: Calibration service providers for audiometric equipment often encounter impracticalities in fully implementing the International Electrotechnical Commission (IEC) guidelines for the extended high frequency region. This report evaluates some of the work-around solutions sometimes employed in practice and the implications these have for audiometer calibration results and uncertainties. Design: The impact of using four different microphone configurations on the ear simulator calibration in the frequency range 125 Hz to 20 kHz, and especially in the extended high frequency range from 10 kHz to 20 kHz, was investigated, at a range of temperatures. Results: Variations in the response of the ear simulator of up to 6 dB were observed with the different microphone configurations. In addition, using the microphone without its protection grid produced a dip in the high frequency response of approximately 15 dB. Conclusion: While deviation from the practices required in IEC standards is not recommended, replacing the microphone protection grid with a specially fabricated collar (essentially a grid with the top removed) was found to constrain deviations in response to within ±2 dB. It was also concluded that simply removing the microphone protection grid resulted in a wholly unsatisfactory performance.
Acknowledgements
The author is grateful to Michael Ekelid and Oliver Sargent at GN Otometrics for providing the motivation for this study, and to Søren Jønsson at Brüel and Kjær Sound and Vibration for providing the microphones and adapters used in the testing.
Declaration of interest
The author reports no conflicts of interest.