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BRUEL & KJAER 2204 - Pistonphone Type 4220

BRUEL & KJAER 2204
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5uch
a
calibration
can
be
carried
out
on
the
B & K
microphones
using
the
B & K
Pistonphone
Type
4220.
After
calibration
it
is
possible
to
perform
sound
level
measurements
to
an
accuracy
of
± o.3 dB
with
the
Precision
Sound
Level
Meter
Type
2203.
The
principle
of
operation
of
the
Pistonphone
is
shown
in
Fig.
7.3.
16612 2
Fig. 7.2.
Assembly
drawing
of
the
Pistonphone.
Reto
i
ni~g
spring
Fig.
7.:J.
Cross-section showing
the
principle
of
operation.
The
two
pistons
are
driven
symmetrically
by
means
of
a
cam
disc,
mounted
on
the
shaft
of
a
battery
driven
miniature
electric
motor.
The
cam,
which
is
made
of
specially
selected,
tempered
steel
and
machined
to
a
high
degree
of
accuracy,
gives
the
pistons
a
sinusoidal
movement
at
a
frequency
equal
to
four
times
the
speed
of
rotation
.
The
cavity
volume
is
therefore
varied
sinusoidally
and
the
RMS
sound
pressure
produced
will
be
2
A.
S
P =
rP·
---=
Vy2
where
r =
c.tc.,
=
ratio
of
specific
heats
for
the
gas in
the
cavil}
P.
==
atmospheric
pressure.
A.
=
area
of
each
piston
.
46

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