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Fig. 2.4. Artificial Ear and Precision Sound Level Meter in combination
.
4. Turn knob 3 fully clockwise.
The mark "Ref" appears in the red circle to the
right.
5. The meter pointer should now deflect to a value, on the upper red
scale, equal to the
k-value'
obtained from the mierophone calibration
chart.
If
it does not, adjust the SENSITIVITY ADJUSTMENT by means
of a screwdriver, until the said condition is
obtained.
NOTE: The instrument should warm up for approximately 15 seconds
before calibration.
6.
Turn knob 2 clockwise until the meter pointer deflects between 0-10 dB,
and the sound pressure level in the artificial ear is measured.
7.
If
the meter pointer does not deflect, when knob 2 is fully
clockwise,
then turn knob 3 counter clockwise, until the pointer deflects between
0-10 dB, and the sound pressure level can he
measured.
Further it is possible to use the Sound Level Meter in connection with
the Level Recorder Type 2305 for automatic recording of the frequency
characteristic of an earphone. The Sound Level Meter must be adjusted
as described above item 1 to 5, and knob 2 (Fig. 2.5) is turned clock-
wise until 100 appears in the red circle to the right. Operations of the
Beat Frequency Oscillator Type 1022 and the Level Recorder Type 2305
are described under "Operation of a Complete Arrangement for the
Testing of the
Earphone".
15
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