(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.