G.R.A.S. Sound & Vibration
Pistonphone Types 42AA/42AA-S1 - Page 14
3.4 Calculation of Microphone Sensitivity
The sensitivity of a microphone under test can be calculated via a measurement of the micro-
phone’s output voltage. If the measured output voltage is V
o
, and the sound pressure level in
the Pistonphone’s coupler is L
C
(decibels), the microphone sensitivity S is given by:
The value 20 μPa is the standard reference sound pressure. The result here includes the load-
ing effect of the preamplier’s input impedance as well as the gain or attenuation within the
preamplier. To measure the “Open Circuit Sensitivity” of the microphone (i.e. when the micro-
phone’s output is not affected by the load of a preamplier), a special preamplier, for example
the G.R.A.S. Type 26AG (which has insert voltage calibration capability), should be used.
S =
(8)
V
o
20 μPa ⋅ 10
L
c
20
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