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D-0126050 rev 1 -
270+ Operating Manual
To calibrate the Right channel (if required) press softkey
F3
to select
RIGHT
(do
not
change the amplifier’s
volume control).
1. Adjust the calibration for all of the right channel frequencies (including 1000Hz) by using the frequency
keys and the Channel 1 rotary control as described above
2. To store the levels and leave Freefield calibration mode, press the softkey
F4
key
3. If required, all calibration levels can be set to a default of zero by pressing
Softkey
F1
(‘Zero all’) while
in freefield calibration mode
It is possible that, because of the characteristics of the listening room or test set-up, the calibration levels listed
above cannot be achieved because the limit of adjustment is reached for one or more frequencies. Re-
arrangement of the listening room may improve the situation, but if not, the following is a possible solution:
•
Set all of the frequencies for which calibration can be achieved
•
For frequencies where this is not possible, adjust each to be a multiple of 5dBs from the required level
•
Produce a correction table for each frequency for which calibration could not be achieved to be applied
to the output level of the audiometer while conducting a test to relate the instrument display to actual
output level from the speakers.
8.6.3.
CALIBRATING THE COMPETING NOISE CHANNEL
This part of the calibration procedure may be omitted if freefield speech calibration is not required.
1. Enter the Freefield calibration mode through the
MENU
2. Press the
F2
softkey and the display will change to indicate the option to adjust the competing noise
calibration level
– the legend “Sp Mask” is used to indicate this
3. Without changing the setting on the external amplifier use the SIGNAL control to adjust the level of
the competing noise to 90dBSPL as measured by the SLM using dBA settings.
4. Calibrate each channel, pressing the RIGHT and LEFT keys to switch between channels
5. If necessary it is possible to switch between speech (competing noise) and warble calibration modes
by pressing SPEECH and WARBLE respectively
6. To store the levels and leave Freefield calibration mode, press the SAVE key
8.7.
FREEFIELD LIVE SPEECH CALIBRATION
Note: Users should be aware that there is a growing body of professional opinion that Live Voice speech
audiometry is generally not recommended. Exceptional skill and concentration are required to achieve
accurate and consistent levels.
1. Connect a microphone to the
MIC1
input on the audiometer
2. Press
SPEECH
and use Softkey 2
to ensure that ‘MIC’ is displayed in capitals (indicating that the
external microphone is selected)
3. The input signal is adjusted in 1dB steps with the Channel 2 rotary control
4. Input signal
adjustment should be made to adjust for the operator’s voice to peak at the 0dB point on
the LEVEL dB bar graph
5. If recorded speech has been calibrated no further action is necessary
6. If recorded speech has not been calibrated, the volume control of the amplifier should be adjusted so
that the SLM reads 90dBSPL at the listening point with a 70dBHL setting on the instrument; note that
this is an approximate setting only, as it is not possible to produce a true calibration signal in live
speech
Summary of Contents for 270+
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