BRUEL & KJAER 4920 User guide
Outdoor Microphone System
Type 4920
The
Outdoor
Microphone
System
extends
the
use
of
the
B & K
Condenser
Microphone
into per-
manent
outdoor
installations
where
the
micro-
phone
is
situated
at
a
considerable
distance
from
the
indicating
instruments.
BHUEL
&
K.Y&R
Ncerum,
Denmark
.
~
80
05
00
•
,;:;."
BRUKJA,
Copenhagen
. Telex:
5316
BB
4920
The
Outdoor
Microphone
System
Type 4920
AUGUST
1964
Contents
1.
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
General
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
The
Amplifier
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Calibration
Oscillator
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
The
Microphone
and
Cathode
Follower
. . . . . . . . . . . . . . . . . . . . . . . . . . 8
The
Wind
Screen
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
The
Rain
Cover
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
Adjustment
of
the
Amplifier
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
Calibration
Oscillator
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Polarization
Voltage
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
3. Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Airport
Noise
Monitoring
......................................
14
Analyses
of
Noise
Signals
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
4.
Specification
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.
Description
General.
The
Outdoor
Microphone
System
Type
4920
has
been
designed
to
enable
outdoor
acoustical
measurements
to
be
made
at
a
considerable
distance
from
the
indicating
instruments.
Fig.
1.1
.
The
Outdoor
Microphone
System
Type
4920.
This
'
~ystem
consists
of:
1. A
preamplifier
and
a
conde
'
nser
microphone
fitted
with
wind
screen,
electrostatic
actuator
and
rain
cover,
and
2.
A
water-
proof
cabinet,
which
encloses
an
amplifier,
a
power
supply
and
a
calibration
oscillator.
This
set-up
will
convert
sound
pressures
into
electrical
signals,
and
due
to
the
low
output
impedance
of
the
amplifier,
these
signals
can
be
transmitted
over
a
lon
g
distance
by
means
of
a
cable,
for
instance
a
telephone
cable
or
a
twisted
pair
of
wires.
An
easy
system
check-out
and
calibratlon
can
be
made
when
the
built-in
electrostatic
actuator
is
switched
into
operation.
Fig.
1.1
shows
the
complete
Outdoor
Microphone
System,
and
its
principle
of
opera~ion
is
given
in
the
form
of
a
block
diagram
in
Fig.
1.2.
3
Wind screen
Rain
Cover
and
electro-
static
Actuator
Microphone
and Cathode
Follower
Waterproof cabinet
~
----
--
--
-
-----
-,
I
~
I
I
I Output
1 Calibrator
on
I
I
.I
I
I
I
L
____
___________
j
tMafo
Fig. 1.2. Bl
ock
diagram
of
the
Outdoor
Microphone
System
Type
4920.
Amplifiei'.
In
this
equipment
a
two
stage
R-C
coup
led
transistorised
amplifier
is
used
in
which
the
transistors
are
in
gr
ounded
emitter
connection.
A
maximum
gain
of
30 dB
can
be
obtained,
and
a
built-in
screwdriver
operated
potentio-
meter
a
ll
ows
gain
variations
of
up
to
31.5
times
the
microphone
signal.
Normally
the
signal
from
the
microphone
and
cathode
follower
is
fed
to
the
screwdriver
operated
potentiometer
through
a
capacitor,
it
is
possible,
however,
to
take
the
signal
directly
from
the
cathode
follower
just
after
lhe
capacitor
at
the
terminal
on
the
printed
circuit
marked
DIR.
OUTP
.
.
ooooooooooooooooooooooooooooodooooooooooooooooooo
B
rll~lc.r
.
5025
z-lMr
·--
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r.:
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.........,~x..~~o
,
._
ooiO~
OP1123
10
1000
10000
..
• c ...
c
.....
f6+878
Fig. 1.3.
Frequency
characteristic
of
the
amplifier
loaded
with
a 200 Q resistor.
4
To
obtain
a
linear
frequency
response,
see
Fig.
1.3, a
heavy,
negative
feed-
back
has
been
introduced.
However,
when
a
long
transmitting
cable
is
con-
nected
to
the
amplifier
output
it
may
be
necessary
to
correct
for
a
drop-off
in
the
response
at
higher
frequencies
to
obtain
the
desired
linear
cha-
racteristic.
This
correction
is
made
by
connecting
a
capacitor
from
the
~
emitter
of
the
first
stage
to
ground
(on
the
printed
circuit
the
mounting
holes
for
this
capacitor
are
marked
C 30).
The
effect
of
the
correction
is
illustrated
in
Fig.
1.4. At
the
output
of
the
amplifier
a
transformer
is
used
..
OODDOOOOOOOOOOOOOOOCJCJDDOOODOODD
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Brll~lat•
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50".
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10
QP1123
10
--
,-
-:-
--t--
+
1000
·
---
10000
20
~~~:
Fig. 1.4.
Frequency
response
correction.
a.
Response
of
amplifier
and
a
long
cable
without
correction.
b.
Response
of
amplifier
with
correction.
c.
Response
of
amplifier
and
a long cable
with
correction.
'
.,
,
•
cu.
cu.
to
obtain
several
output
impedances.
The
secondary
windings
of
this
trans-
forfl,ler
are
detailed
in
Fig.
1.5
and
by
means
of
two
or
three
shorting
links,
it
is
possible
to
use
any
of
the
following
load
impedances:
200
Q,
200 Q
floating,
200 Q
symmetrical
or
50
Q.
The
01.1tput
terminals
of
the
amplifier,
which
are
located
on
the
printed
circuit
can
be
directly
connected
to a
transmission
line,
the
length
of
which
may
be
of
up
to
10
km.
The
amplifier
is
highly
stabilized
varying
less
than
± o.2
QB
for
a ± 10 %
variation
in
line
voltage.
The
long
term
stability
is
expected
to
be
± o.5
dB
when
the
equipment
is
in
continuous
use.
Furthermore
the
amplifier
is
well
temperature
stabilized
and
will
be
virtually
unaffected
from
-30°
C
to
+60° C
if
power
is
drawn
continuously.
See
Fig.
1.6.
5
200.A.
Osc.on o
Di
r.
out
o
<>:1_
200.n
Sym
Osc.
on
.Dir.
out
200..n.
Floating
Osc.on 0
A
mp.ou
t{
~
f-<>
<:J__
Di
r.
out o
SO.n.
Osc.
on
o
Amp.out
Di
r.out
o
16+880
Fig. 1.5.
Load
impedance
conditions.
Calibr
..
tion
Oscillator.
As
mentioned
earlier,
the
microphone
system
contains
a
device
by
which
it
is
poss
·
ible,
without
any
alterations
being
made
to
the
measuring
set-up,
to
make
an
easy
system
check-out
and
calibration.
A
known
voltage
from
6
a
I
/~
r'-b
-1
-2
-20
-10
0 10 20
-
...
-
1',._---
30 40 50
60
Col.signol
rel.90
dB
SPL.
---f-16~-88~
c
Fig. 1.6.
Typical
amplification
and
calibration voltage variations
with
'
temperature.
a
calibration
oscillator
in
the
amplifier
assembly
is
fed
to
an
electrostatic
actuator
built
into
the
microphone
rain
cover.
This
voltage
produces
a
known
force
which
acts
on
the
microphone
diaphragm
and
is
comparable
to
a
sound
pressure.
The
actuator,
delivered
with
the
microphone
system,
is
adjusted
at
the
factory
so
as
to
produce
an
equivalent
SPL
of
90 ± 1
dB
by
the
injection
of
an
AC
voltage
of
215
V,
this
being
the
output
voltage
from
the
calibration
oscillator.
It
is
possible
to
adjust
this
voltage
by
changing
the
resistor
marked
OSC.
VOLT
ADJ
on
the
printed
circuit.
Transm. cable
Osc.
start
Transm. end
Input
to indicating
or analysing instruments
-25V
Receiving end
16+81:3
Fig. 1.7. Connection for
remote
control
of
the
calibration generator.
The
frequency
of
the
oscillator
is 500
Hz
and
it
may
be
adjusted
by
means
of
the
iron
core
marked
OSC.
FREQ.
ADJ.
As
there
is
no
DC
bais
voltage
between
the
actuator
and
the
diaphragm,
the
frequency
of
the
signal
from
the
microphone
itself
will
thus
be
1ooo
Hz.
A
careful
stabilization
of
the
output
voltage
from
this
oscillator
makes
it
practically
independent
of
ambient
temperature
variations.
See
Fig.
1.6
curve
a.
To
operate
the
calibration
oscillator
a
10-25
V
battery
is
connected
either
between
one
of
the
signal
leads
and
ground
(2
wire
system),
see Fig.
1.
7,
or
between
a
special
lead
from
the
amplifier
assembl
y
and
ground
(3
wire
system).
When
using
the
battery
between
signal
lead
a
nd
ground,
care
must
be
taken
not
to
short
circuit
the
signal
or
the
DC
voltag
e.
If
the
indicating
instruments
have
a
capacitor
in
the
input
circuit,
the
DC
voltage
can
be
supplied
through
a 5 k.Q
resistor,
but
in
the
case
of
a
transformer
input
where
the
transformers
are
not
floating,
a
series
capacitor
must
be
used.
7
Microphone Cartridge
Type
4133
and
the
Cathode
Follower
2615.
The
microphone
used
consists
of
a 1/
2"
microphone
cartridge
and
a
cathode
follower
attached
to
a 10 m (30 foot)
cable
between
the
microphone
and
the
amplifier
box.
This
microphone
cartridge
is
screwed
onto
the
housing
of
the
cathode
follower
forming
a
small
rugged
unit.
Connection
of
the
microphone
must
be
made
directly
to
the
input
socket
on
the
amplifier
assembly
which
matches
the
microphone
connecting
plug
.
Stabilized
'
plate
and
heater
voltages
for
the
cathode
follower
and
polarization
voltage
for
the
cartridge
are
available
at
this
seven-pin
socket.
The
200
volt
polarization
voltage
may
be
adjusted
by
means
of
a
potentiometer
marked
POL.
VOLT.
ADJ.
on
the
amplifier
assembly,
with
the
point
for
measuring
this
voltage
marked
MEAS.
The
Microphone
Cartridge
Type
4133
features
a
normal
incidence
free-
field
frequency
characteristic
which
is
flat
up
to
12.5
kHz
(with
rain
cover
mounted).
Fig. 1.8.
The
Wind
Screen
UA 0082.
Wind
Screen.
The
wind
screen
is
designed
for
mounting
on
the
cathode
follower
equipped
with
a
condenser
microphone
cartridge
and
the
rain
cover.
It
is
covered
with
a
double
layer
of
nylon
cloth,
and
gives
an
effective
reduction,
of
the
order
of
10 dB
or
higher
of
wind
induced
noise
at
lower
wind
velocities.
It
is
possible
to
mount
the
1", 1/
2"
or
1/4"
microphone
inside
the
wind
screen,
but
when
mounting
a 1/
2"
or
a 1/
4"
microphone
and
cathode
follower
a
tightening
ring
and
mounting
tube
must
be
used,
refer
to
Fig.
1.9.
The
8
•
. '
Cathode Follower
16+811
with
2 1/8"
mounting
holes
.
Fig. 1.9.
The
Wind
Screen
VA
0082
mounted
on
1/2
cathode
follower.
mounting
tube
is
isolated
from
the
microphone
and
cathode
follower
housing
in
order
to
avoid
a
disturbing
ground
loop,
and
it
is
rhodium
plated
for
corrosion
protection.
When
using
the
wind
screen
with
the
rain
cover
screwed
onto
the
microphone
cartridge,
the
signal
lead
to
the
electrostatic
actuator
inside
the
rain
cover
is
fed
through
a
slot
in
the
tightening
ring.
Shown
in
Fig.
1.10
is
the
free-field
corrections
for
a
microphone
cartridge
Type
4133
and
cathode
follower
equipped
with
a
rain
cover
and
mounted
inside
the
wind
screen.
Rain Cover.
This
special
screen
has
been
developed
to
protect
the
microphone
diaphragm
against
rain
and
extreme
weather
conditions.
A
drawing
of
this
Rain
Cover
9
15
Free- field corrections for
c-----
type
4133
with
Wind
Screen
UA
0082
/""'
f---
and
Rain
Cover
UA0056
I I I /
~
f--
-
-4133
with protecting grid
//
\
r------
.
--4133
with
UA0056+UA0082
/,
\
dB
10
....
o•
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r\
y i
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........
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.......
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......
I
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.......
15o•
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~
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\
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J \
•
-5
-
10
1 6 7 8 9
10
20
30
40
50kHz
70
/6f891
a)
15
Free-
field
corrections
for
I I
f--
type
4133
wi
th Wi
nd
Screen
UA0082
f--
and
Rain
Cover
UA
0056 I
dB
r---
--4133with
protecti
ng
grid
10
r--------4133
with UA0056+UA0082 V"'\
I \\
--
.............
Vfr\
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/"'
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10
20
30
40
50kHz
70
1'6f892
b)
10
15
Free - field corrections
for
I
-type
4133
with
Wind
Screen
UA
0082
-and
Rain
Cover
UA0056
I I
dB
~
--4133
with protecting grid
10
~--4133
with UA0056+ UA0082
I \
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10
20
30
40
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Fr
ee-
fi
eld
corrections
fo
r . I
dB
-
~:de~~~~
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i
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e
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1
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82
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4133
with protecti
ng
grid
-1-t---+-+----1f---+--+--+--t--t
-l
10
1------4133
with UA0056+UA0082
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--+-
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L_
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1 5 6 7 8 9
10
20
d)
30
40
50kHz
70
/6>89~
Fig. 1.10. Free field corrections for
microphon
e cartridge
Type
4133 and
c
athode
follower equipped
with
a rain
cov
er
and
mount
ed inside a
wind
screen.
11
Fig. 1.11.
The
Rain
Cover UA 0056
with
cable for feeding
the
built-in
calibrator
connected
on top.
is
shown
in
Fig.
1.11.
An
electrostatic
actuator
is
built
into
the
rain
cover,
allowing
remote
controlled
calibration
and
check
of
the
installations
to
be
made.
This
rain
cover
/
actuator
when
delivered
with
an
outdoor
microphone
system,
is
adjusted
together
with
the
particular
microphone
cartridge
that
it
will
be
mounted
on,
to
an
equivalent
SPL
of
90 dB
at
215
Volts.
In
case
of
replacement
or
repair
the
complete
cartridge
+
rain
cover
assembly
should
be
returned
to
the
factory.
The
maximum ambient
temperature
for
the
cartridge
and
rain
cover
is
80°
C and it is
only
fully
protected
when
the
associated
cathode
follower
is
permanently
heated.
pooooooooooooo
D D 0 D D 0 0 D D D 0
.....
Ki-
0° incidence
......
KJ-
=Type
UA0056
+ 4133+2614/15
Sensitivit~
limits
=
==
for
any
incidence
5db
Random
incidenc~
200
500
1000
2000
....
10000
20000
"'
1900
CIS
10000
ASZJWJ
Fig. 1.12.
Response
of
a
half-inch
microphone
fitted
with
a
Rain
Cover
UA
(;056.
The
increase
in
sensitivity
at
high
frequencies
may
easily
be
com-
pensated
for
by
appropriate
loading
of
the
microphone
output.
12
2.
Operation
Adjustment
of
the Amplifier.
The
microphone
system
may
be
used
in
the
range
from
approx.
GO
dB
to
150 dB
SPL.
When
the
Outdoor
Microphone
System
is
connected
to
a
tele-
phone
cable
the
cross
talk
from
neighbour
lines
may
cause
trouble
which
will
determine
the
lower
limit
for
the
transmitted
signal.
The
built-in
amplifier
will,
however,
enable
some
adjustment
of
the
microphone
output
voltage
level
to
the
telephone
line.
At
the
200 Q
output
of
the
transformer
the
maximum
signal
handling
capacity
will
be
3 V
r.m.s.
and
for
50
.Q,
1.5 V
r.m.s.
at
200
Q
the
gain
is
30 dB
and
at
50
.Q,
24
dB
therefore
the
gain
should
be
adjusted
so
that
the
3 V
r.m.s.
(1.5 V r.m.s.)
is
obtained
for
the
highest
signal
level
expected.
This
means
that:
For
a
microphone
cartridge
sensitivity
of
1 mV/,
,ubar
the
gain
adjustment
may
be
at
maximum
for
any
measurement
of
SPL's
up
to
114 dB.
For
SPL's
above
114
dB
the
gain
adjustment
should
be
reduced
by
as
many
dB
as
the
SPL.
is
expected
to
exceed
114 dB.
This
will
ensure
the
best
possible
signal
to
noise
ratio
on
the
cable.
Calibration Oscillator.
The
electrostatic
actuator
inside
the
rain
cover
is
adjusted
at
the
factory
so
as
to
obtain
a
SPL
of
90 dB
by
the
injection
of
an
AC
voltage
of
215 V.
Normally
it
should
not
be
necessary
to
adjust
this
voltage
from
the
calibra-
tion
oscillator,
but
if
it
is
found
necessary
to
do
so,
it
can
be
adjusted
by
changing
the
parallel
resistor
marked
OSC.
VOLT.
ADJ.
on
the
printed
circuit.
Furthermore
it
is
possible
to
adjust
the
oscillator
frequency
by
means
of
the
iron
core
marked
OSC.
FREQ.
ADJ.
this
frequency
should
be
500
Hz
in
order
to
produce
a
1ooo
Hz
signal
from
the
microphone.
Polarization Voltage.
The
polarization
voltage
of
200 V
for
the
microphone
cartridge
can
be
adjusted
by
means
of
the
potentiometer
marked
POL.
VOLT.
ADJ.
this
voltage
can
be
measured
at
the
point
marked
MEAS.
13
3.
Application
Airport
Noise
Monitoring
System.
In
recent
years
it
has
been
obvious
that
the
noise
from
aircraft
taking
off
and
landing
at
commercial
airports
in
the
neighbourhood
of
large
cities
has
raised
a
tremendous
problem
for
people
living
in
the
vicinity
of
the
airport.
Many
measurements
have
been
carried
out,
and
the
sound
from
different
types
of
planes
under
various
conditions
of
loading,
power,
rate
of
climb,
speed,
height
etc.
has
been
analyzed.
The
purpose
of
the
system
shown
in
Fig.
3.1
is
to
monitor
the
noise
of
every
aircraft
taking
off
or
landing
in
directions
where
noise
disturbance
may
be
exptected,
and
in
order
to
avoid
criticism
of
the
system
and
the
technique,
the
accuracy
of
these
measure-
14
Windscreen UA0082
Rain
Cover
UA
0056
/Microphone
Cartridge
4133
Co
thode Follower
box
10m
...__
__
__,
min.2
conductor
Main Unit
in
.the
Control Tower
ZH
0002
Control Panel
I
Distance
up
l
to
10
km
cable
2212
Microphone
system
in
the field
Noise
Limit Indicator
ft.'t&f~
Fig. 3.1.
The
different
parts in the complete noise
limit
indicator set-up.
ments
must
be
high.
Both
the
absolute
accuracy
of
the
system
and
also
the
long
term
stability
are
extremely
important
factors.
For
such
measurements
the
Outdoor
Microphone
System
Type
4920
is
used
as
shown
in
the
figure,
connected
by
a
normal
telephone
cable
to
the
measul'ing
unit
in
the
airport
control
tower.
Here
all
the
lines
from
the
microphone
positions
are
fed
to
the
Noise
Limit
Indicator
Type
2212.
Sound
limit
indications
are
given
on
a
small
control
box
by
one
or
more
of
the
red
lamps
lightin
g
up
if
the
sound
limit
is
exceeded
at
any
of
the
microphone
positions.
This
control
box
also
contains
some
pushbuttons
for
starting
and
stopping
the
whole
measuring
procedure.
Analysis
of
Noise Signals.
A
very
convenient
method
of
measuring
trafic
noise
vs.
time
over
a
long
period
for
instance,
would
be
to
install
the
Outdoor
Microphone
System
9
10mj
~
~
"'"''"'~"'------<>
4920
9
~~
10m'
I
~~:_1Q_15,!n
4920
Fig. 3.2.
Practical
measuring
set-up
foJ"
field
noise
measurement.
Type
4920.
By
employing
several
of
these
systems,
it
is
possible
to
take
measurements
at
different
positions
covering
a
large
area,
as
the
signals
detected
by
each
different
Microphone
System
can
be
fed
back
to
only
one
set
of
data
reduction
equipment
where
the
sound
pressure
level,
statistical
distribution
of
the
noise
or
the
spectrogram
can
be
measured.
Due
to
the
fact
that
the
transmitting
cable
between
Microphone
Systems
and
indicating
instrument
can
be
up
to
10
km
long,
the
indicating
and
analyzing
equip
-
ment
may
be
situated
at
any
suitable
place
within
this
.
distance.
In
the
particular
arrangement
shown
in
Fig.
3.2
spectrograms
of
the
noise
signal
can
be
recorded
automatically
on
the
frequency
calibrated
paper
of
the
15
Level
Recorder
Type
2305
either
in
narrow
bands,
or,
when
the
Selective
Section
of
the
Frequency
Analyzer
Type
2107 is
switched
out,
and
the
Band
Pass
Filter
Type
1612
is
switched
in
as
external
filter,
in
1/1
or
1/3
octave
bands.
Again
switching
the
selective
section
of
the
Frequency
Analyzer
out,
this
instrument
can
be
used
as
a
microphone
amplifier
where
provided
that
the
instrument
has
been
calibrated
correctly,
the
Sound
Pressure
Level
of
the
noise
signal
can
be
read
directly
off
the
instruments
indicating
meter.
The
statistical
distribution
of
the
noise
signal
may
be
recorded
over
24
hours
if
so
desired.
This
is
achieved
by
employing
the
Statistical
Distribution
Analyzer
Type
4420
connected
to
the
Level
Recorder,
and
using
the
Frequency
Analyzer
as
an
amplifier.
16
Frequency
Characteristics:
Electrical
System:
Acoustical
System:
Amplification:
Noise:
Output:
Calibration:
Stability:
Temperature
and
Humidity:
Microphone
Sensitivity:
Specification
{+
~·
2
dB 20-
40ooo
Hz
No
load
+
~·
2
dB 20-
18ooo
Hz
Nominal
load
{
~
~
dB
25-5ooo
Hz
Random
incidence
+
~
dB
Sooo-125
00
Hz
Random
incidence
Max. 30 dB
continuously
variable
downwards.
<40 p,V
referred
to
the
input
terminals.
200 Q No
load
max.
3
Vrm
s
Loaded
max.
2.2 V
rm
s
50 Q No
load
max.
1.5 V
rms
Loaded
max.
1.1
Vrm
s
90 ± 1 dB
from
the
el
ec
tro
static
actuator
inside
th
e
rain
cover
for
215 V
AC
from
the
built-in
genera
tor.
Variation
is l
ess
than
± o.2
dB
for
a ± 10 %
vari-
a
tion
in
line
voltage.
Long
te
rm
stability
± o.5
dB
to
be
expected
when
continuously
connected
.
Life
e
xpectancy
more
than
20ooo
hours
for
elec
tronic
parts
,
when
continuously
switched
on.
(Based
on
factory
tests
but
without
obligations).
For
micro-
phone
cartridge
in
normal
country
atmosphere
the
life
expec
tanc
y is
the
same
but
may
be
somew
hat
low
er
in
very
corrosive
atmospheres.
Virtually
unaffected
from
-
30°
C
to
+60° C
if
power
is
drawn
continuously.
1
mV
/,ubar.
17
Dynamic
Range: 60 dB-160 dB
depending
on
amplifier
potentiometer
setting.
The
Outdoor
Microphone
System
can
be
operated
from
240, 220, 150, 127, 115,
or
100 V AC
power
line,
the
proper
condition
is
selectable
by
a
switch-fuse
combination.
Power
consumption
approx.
15
W .
18
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