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For calibration, the measuring microphone of a sound level meter
(SLM) is placed at the reference point (the point that the subject’s
head will be located).
The procedures outlined below cover calibration for both speech
and warble tone modes of audiometry. If both modes are to be use
then speech calibration must be carried out first. If only warble
mode is to be used then only the warble part of the calibration pro-
cedure may be carried out.
However, if speech mode is required later (and a speech calibration
is performed) this will invalidate any previous warble calibration
which would then need to be repeated. If warble tones are to be
used as a means of equalising the frequency response in the spee-
ch calibration (see Section 4.1.1 of this appendix) then this will in-
validate any previous warble calibration which would then need to
be repeated when warble tone testing is required.
4. Free-field Speech Calibration
This is carried out in two stages:
1) the speech channel, which contains two elements:
• an optional equalisation phase
• a level-setting phase
2) the competing noise channel, which may be omitted if
competing noise is not required.