SM010-3 Siemens SD 270 Operating & Service Manual Page 33
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 5 of this appendix) 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.
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
4.2
Calibrating the Competing Noise Channel
Refer directly to Section 5.2 of this appendix 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