2. Operation
The calibrator
is
made
for
calibration
of
1 in and
1/2
in diameter micro-
phones.
An
adaptor
is
placed in the
front
opening
for
use
with
1/2
in
microphones, and this adaptor
is
removed when 1 in microphones
are
cali-
brated. (Fig.2.1)
Fig. 2.1. Calibrator
with
Adaptor
for
1
/2"
Microphone ..
The sound pressure level
of
the
calibrator
is
94
dB. However,
because
of
the
increase in sound pressure at a microphone diaphragm when placed in a free
sound field (Fig.2.3), there
is
a small correction
to
be
subtracted
from
the
calibration value when calibrating free field microphones. This correction
is
0.4 dB
for
1 in microphones and 0.2 dB
for
1/2
in microphones.
For
pressure microphones no correction
is
required.
4
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