Audio Engineering

Microphone Technology 641

The open circuit voltage output of the microphone when exposed to some other arbitrary
acoustic level LP is calculated from

Eo

SLVP





10

94

20

⎛

⎝

⎜⎜⎜

⎜

⎞

⎠

⎟⎟⎟

⎟ (22.2)

where Eo is now the open circuit voltage output of the microphone for an arbitrary
acoustic input of level LP.

For example, suppose a sample microphone is tested by the conditions of Figure 22.1
with the result that the open circuit voltage is found to be 0.001 V. The voltage sensitivity
of this microphone as calculated from Equation (22.1) is then

SV 



20 0 001

60

dB

dB.

log(. )

This result would be read as .60 dB referenced to 0 dB being 1 V per pascal (1 V/Pa).
If this same microphone were exposed to an acoustic input level of 100 dB rather than
the test value of 94 dB, then its open circuit output voltage from Equation (22.2) would
become

Eo



 

10

0 002

60 100 94

20

⎛

⎝

⎜⎜⎜ ⎞

⎠

⎟⎟⎟

⎟

.V.

Many current microphone preamplifi ers have input impedances that are at least an
order of magnitude or larger than the output impedances of commonly encountered
microphones. In such instances, Equation (22.2) can be employed to determine the
maximum voltage that a given microphone and sound fi eld will supply to the preamplifi er
input. The voltage sensitivity of Equation (22.1) is the one currently employed by most
microphone manufacturers.

Another useful sensitivity rating for a microphone is that of power sensitivity. In this
instance the focus is placed upon the maximum power that the microphone can deliver to
a successive device such as a microphone preamplifi er when the microphone is exposed
to a reference sound fi eld. In this instance the reference power is 1 mW or 0 dBm and