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3. Turn the switch AUTOMATIC SCANNING to "Off".
4. Turn FREQUENCY INCREMENT knob until the pointer of the incre-
mental frequency scale is at
"0
Hz".
5. Set
MODULATION FREQUENCY to "Mod. Off".
6. Set the COMPRESSOR SPEED switch to "Comp. Off".
7. Turn OUTPUT LEVEL until the pointer of the indicating meter is
positioned at "12" at the upper scale.
8. Set MATCHING IMPEDANCE switch to "Att.".
9. Set ATTENUATOR to "120 mV", or another desired value.
Connect the attenuator output to the input terminals of the earphone
under test.
Assemble the artificial ear as described under "Operation of the Artificial
Ear" page 10, and use the coupler suited for the earphone.
·
Adjustment of the Microphone Amplifier.
1. Check the microphone polarization voltage.
2. Connect the condenser microphone in the artificial ear to the micro-
phone amplifier as shown in Fig. 2.1.
3. Set the contrql knobs in the following positions:
INPUT SWITCH:
"Condenser
Microphone".
METER RANGE: "Ref".
METER SWITCH:
"Fast-RMS".
RANGE MULTIPLIER: "0 dB X
1".
WEIGHTING NETWORK:
"Linear,
2-40ooo Hz".
Control
k~obs
not mentioned can be in any position.
4. Allow 2 minutes to warm up.
5. Next note the correction factor
"k"
from the calibration chart of the
microphone.
6. With a screwdriver turn the potentiometer SENSITIVITY-CONDENSER
MICROPHONE until the meter pointer deflects to the red mark
+
the
"k" factor in dB. If the "k" factor is negative it has to be subtracted
from the dB value which corresponds to the red mark.
7. Turn METER RANGE to
"100
dB SL" (or another desired value).
8. Connect the Microphone Amplifier to the Level Recorder as shown in
Fig. 2.1.
The Level Recorder.
50 dB potentiometer
'~
used.
1. PO"WER and MOTOR toggle switches to
"On".
2. POTENTIOMETER RANGE to "50".
12
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