AmpliVox 270+ - 8.7. FREEFIELD LIVE SPEECH CALIBRATION; Live Speech Calibration Considerations

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D-0126050 rev 1 - 270+ Operating Manual
• 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
8.5.4. CALIBRATING THE COMPETING NOISE CHANNEL
Identify if a warble tone calibration is not to be carried out. If warble tones are to be calibrated (or if the warble
tone calibration method is used to equalise the speech frequency response) then the competing noise channel
may be calibrated after the warble procedure as the instrument will already be in the appropriate display mode
for this operation.
8.6. FREEFIELD WARBLE TONES CALIBRATION
8.6.1. ENTERING FREE FIELD CALIBRATION MODE
• Press MENU, press F1 key to enter Config and move through the menu items and access the SET
FREFIELD LEVELS screen. Select the YES key.
• Press Save and you are now presented with the freefield calibration screen for Warble tones.
• The audiometer will now output at 70dBHL from the Left channel.
As reference for the calibration of warble tone sound pressure levels, the values from ISO 389-7, Table 1 are
used (binaural, on-axis).
FREQ [HZ]
125
250
500
750
1000
1500
2000
3000
4000
6000
8000
DB SPL
92
81
74
72
72
70.5
68.5
64
63.5
72.5
81.5
8.6.2. CALIBRATION PROCEDURE
If a calibration of the speech channel
has already been carried out:
Adjust the calibration level for the 1kHz, Left channel using the
Channel 1 rotary control to reach the SPL level specified above
as measured by the SLM.
If a calibration of the speech channel
is not required:
The output of the external amplifier should be set in order to
achieve the level specified above at 1000Hz (i.e. 72dBSPL) as
measured by the SLM with the audiometer set to 0dB
compensation. The amplifier’s level control should not then be
changed.
When 1kHz calibration is complete continue with the calibration of the other frequencies of channel 1:
At every other frequency the adjustment should then be made as follows to give the above values as measured
by the SLM.
1. Change frequency using the frequency keys and then adjust the calibration level for the new frequency
using the Channel 1 rotary control to reach the correct level as measured by the SLM
2. Repeat the above until all frequencies have been calibrated for the Left channel