Table of Contents
Advertisement
30
A source of known and adjustable voltage, Ec, is then connected in series with the mic-
rophone (position "b" on the figure). This insert voltage is adjusted until the input vol-
tage to the amplifier is the same (V) again. Then Eo = Ec and the open circuit voltage
sensitivity can be calculated as follows:
Open Circuit Voltage Sensitivity= E c I sound pressure.
When the 2627 is used with the 2010, the insert voltage Ec can be supplied in two
ways. The internal reference oscillator can be used to give a voltage at a fixed frequency
of 1 kHz, or the BFO section of the 2010, or an external generator, can be used to give
a signal at any other required frequency.
It is also necessary to have a sound source of known pressure level and frequency. This
can be provided in two convenient ways:
a)
The Sound Level Calibrator Type 4230 produces a signal at 1 kHz, 94 dB SPL, and
may be used when the insert voltage is supplied by either the internal reference os-
cillator or by the BFO section of the 2010 or by an external generator.
b)
The Pistonphone Type 4220 produces a signal at 250Hz, 124 dB SPL, and may be
used when the insert voltage is supplied by the BFO section or by an external gener-
ator. Using the normal voltage scale supplied with the 201 0 (SA 0051 ), recom-
mended procedures are as follows.
Using the internal reference oscillator
1.
Fit the microphone to the 2627 Preamplifier and connect the 2627 to the PREAMP:
input of the 2010.
2.
Set the controls as follows:
GAIN CONTROL
OUTPUT SECTION ATIENUATOR
INPUT SECTION ATIENUATOR
EFFECTIVE AVERAGING TIME
READ OUT SELECTOR
FREQUENCY RESPONSE
INPUT
"Cal."
"x
1 "
"1 00 mV"
"Fast"
"Lin.", "AC" or "DC"
"Linear"
"Preamp."
3.
Fit the Sound Level Calibrator 4230 on the microphone and press the Calibrator but-
ton. Note the voltage V indicated on the meter scale.
4.
Wait until the Sound Level Calibrator switches itself off, but do not remove it from
the microphone. This is to ensure the microphone is terminated in the same acousti-
cal impedance. Then depress the INSERT VOLT. CAL. "Int." push button on the
201 0. Then adjust the GAIN CONTROL until the voltage V is the same as before.
5.
The calibration voltage from the reference oscillator is then equivalent to the open
circuit voltage E
0
of the microphone. This calibration voltage Ec can be measured by
depressing the "Ref 50 mV" push button and reading the meter without adjusting
the GAIN CONTROL.
Then:
Open Circuit Voltage Sensitivity= Ec I Sound Pressure.
Advertisement
Table of Contents
