AmpliVox 260 - A2.2 External Amplifier and Loudspeaker; A2.3 Calibration Overview

APPENDIX 2 - FREE FIELD CALIBRATION PROCEDURE
34 MODEL 260 INSTRUCTION FOR USE
A2.4.2 Calibrating the Competing Noise Channel
Refer directly to Section A2.5.2 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.
A2.5 FREE-FIELD WARBLE TONES CALIBRATION
A2.5.1 Entering Free Field Calibration Mode
• Press and hold the MENU key and then use the MENU SELECT keys to move through the menu items and
access ‘Set freefield level?’
• Press the YES key, release the MENU key 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
If a calibration of the speech channel has already been carried out:
Adjust the calibration level for the 1kHz, Left channel using the SIGNAL  keys 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, Left channel has been calibrated:
At every other frequency the adjustment should then be made as follows to give the above values as measured by the
SLM.
• Change frequency using the FREQUENCY   keys and then adjust the calibration level for the new
frequency using the SIGNAL  keys to reach the correct level as measured by the SLM
• Repeat the above until all frequencies have been calibrated for the Left channel
• To calibrate the Right channel (if required) press the RIGHT key (do not change the amplifier’s volume
control)
• Adjust the calibration for all of the right channel frequencies (including 1000Hz) by using the FREQUENCY 
 keys and the SIGNAL  keys as described above
• To store the levels and leave Free-field calibration mode, press the MENU key
• If required, all calibration levels can be set to a default of zero by pressing the +20dB key while in free-field
calibration mode