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Using B. F. 0. section or an external generator
1. Connect the generator output to the EXT. INSERT VOLTAGE
socket on the rear panel of the 201 0.
2. Fit the microphone to the 2627 preamplifier and connect to the
PREAMP. input of the 2010.
3. Apply the sound source to the microphone: If the Pistonphone
Type 4220 is used, this involves fitting the Pistonphone onto the
microphone and moving the switch to the "Measure" position. Note
the voltage V indicated on the meter of the 201 0.
4. Switch the Pistonphone off, but leave the Pistonphone mounted on
the microphone to ensure that the microphone is terminated in the
same acoustical impedance.
Adjust the frequency of the generator to be the same as that of the
sound source. Depress the push-button INSERT VOLT. CAL. "E~t."
and adjust the output of the generator until the voltage V indicated is
the same as before.
5. Then the calibration voltage from the generator is equivalent to the
open circuit voltage E
0
of the microphone. This calibration voltage,
Ec, can be measured by taking a lead from the output of the generator
to the DIRECT input of the 2010. The calibration voltage then can
be read directly on the meter scale by depressing the "Direct" INPUT
and CAL. OFF push-buttons.
The output from the generator should be terminated in the EXT.
INSERT VOLTAGE socket on the rear panel of the instrument while
the calibrating voltage is being read from the meter.
Again:
Open Circuit Voltage Sensitivity=
Ec
Sound Pressure
N.B.
30
a) If the Type 4220 Pistonphone is used it produces a sound pressure
level of approx. 124 dB= 31.6 N/m
2 .
The generator frequency should
be adjusted to 250 Hz.
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