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BRUEL & KJAER 2204 - Measurement of Sound

BRUEL & KJAER 2204
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now
deflect
to
within
the
area
marked
"Battery''.
If
it
does
not,
replace
the
batteries.
To
do
this
unscrew
the
battery
compartment
cover
at
the
end
of
the
instrument.
Remove
the
centre
cell
followed
by
the
other
two
and
clean
out
all
dust
and
corroded
material
with
a
soft
rag.
Never
use
abrasives
as
this
will
damage
the
gold
plating
on
the
battery
contacts.
Replace
the
batteries,
centre
cell
last,
with
three
Mallory
RM42K
(or
three
ordinary
1.5 V
torch
batteries).
To
check
the
amplifiers
and
meter
circuit
proceed
as
follows:-
Set
KNOB 1
to
position
"Lin"
and
turn
KNOB 3
fully
clockwise.
Turn
KNOB 2
fully
anticlockwise
so
that
the
"Ref''
mark
appe
·
ars
in
the
red
circle
to
the
right.
The
meter
pointer
should
now
deflect
to
a
value
on
the
upper
red
scale
equal
to
the
K-value
of
the
microphone,
obtained
from
the
microphone
calibration
chart.
If
it
does
not,
adjust
the
sensitivity
by
means
of
the
sensitivity
potentiometer
until
said
condition
is
obtained.
Note:
The
instrument
should
warm
up
for
about
20
seconds
before
calibration
.
The
Sound
Level Meter is
now
ready
for
use. See also
Chapter
7
for
acoustical
calibration
of
the
instrument.
In
cases
when
a
1/2''
microphone
is
used
with
the
instrument,
the
"Ref."
deflection
should
be
adjusted
to
zero
on
the
meter
scale
and
the
K-value
added
to
the
measured sound
levels.
The
K-value is
found
from
.
the
calibration
chart
supplie
·d
with
each
micro-
phone.
Measurement
of
Sound.
When
measuring
sound
the
Sound
Level
Meter
is
used
as
follows:
-
1.
Pull
out
KNOB
1.
2.
Check
the
instrument
as
outlined
under
"Calibration
Checks".
3.
Set
KNOB 1
to
position
"Lin.".
4.
Rotate
KNOB 2
clockwise
until
a
meter
deflection
between
0
and
10
dB
is
obtained.
5.
Set
KNOB 1
to
the
desired
function
.
6.
If
necessary,
rotate
KNOB 3
counterclockwise
to
obtain
a
deflection
between
0
and
10 dB. Note: Do
not
use
KNOB 2
at
this
stage,
in
order
not
to
overdrive
the
input
amplifier.
The
reading
on
the
meter
scale
together
with
the
value
shown
in
the
red
circle
gives
the
result
of
the
measure-
ment.
Always
state
which
weighting
network
has
been
used
when
quoting
sound
levels, e.g. 60 dB
(A)
or
58 dB (B).
It
will
be
clear
from
a
study
of
Fig. 1.3
that
the
difference
between
A
and
C
readings
is a
rough
measure
of
the
low
frequency
content
of
the
signal investigated.
The
choice
of
curve
to
be
used
is
left
to
the
decision
of
the
operator
who
should
appreciate
the
particular
requirements
of
the
noise
problem
in
hand.
22

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