Otorhinolaryngology

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The effect of fequency tolerance on audiometer accuracy
(Health & Medical Publishing Group, 1977) Guelke, R. W.; Floyd, J. D.; Van Zyl, F. J.
Investigations into the methods used to calibrate audiometers reveal that the 6000 Hz frequency is particularly liable to yield inconsistent results when calibrated in the usual way. It is shown that the TDH39 telephone receiver which is usually calibrated on a 9A coupler in accordance with the International Standards Organization recommendation R389 will depend to a considerable extent on the precise frequency used and may differ by as much as 7 db when the frequency is varied but still retained within the specified tolerance limits. A new telephone receiver, the TDH50, is much less sensitive to frequency variation. It is shown that this receiver should be calibrated with the same threshold figures as the TDH39.