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BRUEL & KJAER 4220 - Page 22

BRUEL & KJAER 4220
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control
knobs
and
the
meter
deflection
as
explained
above
.. A
suitable
in-
crease
of
sensitivity
should
be
given
the
amplifier
by
means
of
the
attenuators
in
order
to
obtain
a
convenient
deviation
of
the
pointer
during
the
calibration.
For
example,
in
the
case
of
the
half-inch
microphone
having
a sensitivity
which
is
around
14 dB
lower
than
the
one-inch
microphone,
the
sensitivity
of
the
measuring
instrument
can
be
increased
by
20
dB
by
shifting
the
METER
RANGE
switch
one
step
down
with
respect
to
the
adjustment
in-
dicated
for
the
one-inch
microphones.
The
pointer
will
then
deflect
around
20 dB (full deflection)
when
calibrating
with
the
124 dB S.P.L.
of
the
Piston-
phone
.
If
now
the
deflection
is
adjusted,
by
means
of
the
SENSITIVITY
CONDENSER
MICROPHONE
potentiometer
to
exactly 20 dB,
the
global
reading
is 110 dB,
while
the
sound
level is 124 dB,
which
means
immediately
that
the
correction
to
be
made
on
.
the
global
reading
is +
14
dB.
With
a
Pistonphone
producing
123.8
dB
S.L.,
the
correction
is
exactly
+ 13.8 dB etc.
By
this
procedure,
the
correction
is
determined
with
an
error
which
is
equ~l
to
the
pistonphone
calibration
error
(less
than
± o.2 dB)
plus
the
reading
error.
Referenee level
on
Sound
Level Reeordings
and
Spedropam&.
The
recording
of
the
Sound
Level as a
function
of
time
can
be
made
by
means
of
a level
recorder,
such
as
the
B & K
High
Speed
Level
Recorder
2305
connected
to
the
output
of
the
measuring
instrument.
In
addition,
the
Analyzer
Type
2107
and
the
Spectrometer
Type
2112
are
often
used in
connection
with
the
B & K Level Recorders
in
order
to
obtain
the
frequency
distribution
of
the
sound
being
investigated.
They
are
designed
to
be
driven
synchronously
with
the
pre-calibrated
recording
paper
of
the
level
20
4220
4132
2613
=
.
.
2112
•
~-~lr-------------------------
2305
/60S'S
.Jig. 16. Calibration
of
a
set-up
for frequency analysis
of
noise
.

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