AmpliVox 260 - A1.8 Free Field Recorded Speech Audiometry With Competing Noise (Recorded)

APPENDIX 2 - FREE FIELD CALIBRATION PROCEDURE
33 MODEL 260 INSTRUCTION FOR USE
2) the competing noise channel, which may be omitted if competing noise is not required
A2.4.1 Calibrating the Speech Channel
A2.4.1.1 Equalisation (Optional)
To perform equalisation, connect an external speech source to the audiometer (e.g. CD or tape player). From the default
(switch-on) condition of the audiometer select SPEECH and FREEFIELD and then play the test signal from the speech
recording. This should either be:
• pink noise used with a third-octave spectrum analyser and the SLM
• third-octave noise bands used with the SLM
Use the SIGNAL control to set the output to 70dBHL, and adjust the external amplifier to give a reading of 90dBSPL as
measured by the SLM at the reference point.
The response should then be checked to be within the following limits (IEC 60645-2:1993 Section 10.1):
Frequency Range (Hz)
Tolerance (dB)
125 to 250
+0/-10
250 to 4000
+3/-3
4000 to 6300
+5/-5
If necessary, adjustments should be made using the amplifier controls or an additional graphic equalizer to achieve this
response.
As an alternative to using an external speech source, the warble-tone calibration method and controls (see Section A2.5)
may be used to achieve this response. Note that this will invalidate any previous free-field warble tone calibration, and
this must be repeated when warble tone testing is required.
A2.4.1.2 Level Setting
The calibration tone from the speech recording should be played and the external amplifier volume control used to give
a reading of 90dBSPL for a 70dBHL instrument setting. Once set, no further adjustment should be made to the external
amplifier or graphic equalizer controls (if used for equalisation).
If more than one set of test recordings is to be used then the following procedure can be used to allow for minor
differences in calibration levels:
• Set up as above for the most commonly used test recording
• Measure the actual listening point level for when playing the calibration tone of each alternative set of test
recordings
• For each alternative set of test recordings produce a correction table (the difference between the actual
listening point level measured and 90dBSPL)
• Apply this correction to the output level of the audiometer while conducting a test to compensate for the
minor difference in calibration level