BRUEL & KJAER 4230 User guide

Portable Acoustic Calibrator
e
J
A simple to use pocket size acoustic calibra -
tor . Gives accurate sound pressure level of
94 dB at 1000 Hz.
BAUEL& K.'-'AC.A
N~RUM , DENMARK. Teleph.: 80 05 00 . Cable: BRUKJA. Telex: 5316. COPENHAGEN
030 BB 0103

Sound Level Calibrator
Type 4230
A portable, lightweight acoustic calibrator for accurate field calibration
of sound level meters and microphone systems. Sound level 94 dB,
independent
of static pressure and microphone volume. 1000 Hz fre-
quency gives independence of weighting networks.
June 1969

CONTENTS
1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.
Further calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5. 'Specifications .......................................... 12

1. Purpose
Type 4230 is a portable lightweight acoustic calibrator for accurate field
calibration
of sound level meters and other sound measuring systems. It fits
all B & K sound level meters and microphones of 1 in and 1/2 in diameter.
A unique construction gives a high equivalent volume
of the calibrator, and
the sound pressure developed
is, therefore, independent of microphone vo-
lume. This means
that exact fitting of the microphone in the coupler is not
critical, and that different microphones can be compared without correction
for equivalent volume.
The calibrator
is virtually unaffected by variations in static pressure and
works accurately
within a wide temperature range.
The sound pressure level developed
is 94 dB re 2x1o-5 Nfm2 (1 Nfm2) and
the accuracy
of calibration is better than ±0.3 dB. A frequency of 1000 Hz
has been chosen, to give independence of the weighting networks A, B, C
and D
used with many sound level meters. These have a common reference
at 1000Hz.
The operation of the calibrator is extremely easy: just fit the microphone
into the cavity, press the button on the calibrator and adjust your meter to
correct reading.
3

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

Procedure
1. Place the microphone into the coupler of the calibrator (Fig.2.2)
2. Press the button on the calibrator
3. Adjust the sound level meter to read according to the following
table:
Fig. 2.2. Calibrator fitted on 2205 Sound level meter.
Microphone used
Pressure
4132,4144
type 4134
Free field 4117,4131
type 4145
4133,4148
Sound Level or Sound
Pressure Level
94 dB
93.6 dB
93.8 dB
5

6
15
dB
10
-5
-10
-1
5
I I I
E xc ess of P. over P, /
r- - fo _ r ~ a _ 1 ' _ ' . d ~ ia _ m _ ic _ ro+ph ~ o ~ ne +-4-4-+4-H --,~ -r / ~~--r--r-+-+
1
/
r- --+--t----+--+--+--+-+-+ -utv'--,--_30 ... ~ I'
/ \\
I
v. II·
IV II
.0 so \i I
Ciao•
90• \
1--- -- +---+---+--+ - -+ 1-15~ -~ · \ \ I
I r--'N, \\ \ I
12o"~ \\
i
!fl
'I
!
I
i
! "
I I/
I ~\ \ 1 '.
I \~ \ ! I il\
· ~ -:-;-:+-,+-+ 1 +-----4 \.-\\1\- \\ -\l-,-1 1 !-+--l--+ -4i ·H
- ~e·o·lncidence \\,\ i _ o.1 - ~
1kHz
I
I I I 8 I '\ 1 \l ?. \· A Jl-f--
- I ~1\-f'i
4 5 5 7 8 9 10
I
15 20 30 40 50 70
/6 9/S4
b ~ ld correctio ~ s
for Type 4133 and 4134
v \
0
r- with protect i ng grid
./ \
/o·
\
/ I
v
3Q-'
.......
I
//
5
//
V/ \
\
k-:::
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so·
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}{!'~O J ~ ~ ,-
... ~
1-
,,
-r-; r-- \
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b I 12o·1SO\
I I I I T
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0 I I I I I \\ \ \
2kHz 3 4 5 10
15 20
30 40 so 70 100 15~
619
:., oo
Fig. 2.3. Pressure characteristics with B & K 1" and
1 /2" Microphones.
,..

Battery change
If the signal does not last for at least a few seconds after the pushbutton on
the calibrator has been released, the battery is replaceable. This is done after
unscrewing
the bottom black part of the calibration housing.
Fig. 2.4. Insertion of 9 V-battery in the Calibrator.
7

3. Description
The calibrator is based on a 1000 Hz stabilized oscillator which drives a
piezoelectric bender. This bender is coupled to a membrane which produces
a sound pressure in
the coupler volume. As the system is adjusted to reso-
Fig.
3. 1. Operation of 4230.
nate at 1000 Hz and is driven at this frequency, the equivalent volume is
very high. In order to avoid influence on the stiffness of the volume behind
the diaphragm
caused by change in static pressure, a Helmholz-resonator
construction is made. (Fig.3.2)
A
built-in temperature compensation ensures accurate calibration over the
whole temperature range of the calibrator.(Fig.3.3)
A hold circuit is included to facilitate operation. This circuit holds the signal
8

Sound level
[dB] ±0.05dB/100
mbar
94.3
94.2
[/~
vW$ 0 [/~
[/ ~
~
v ~
[/ ~
W#~ ~&
I) ~
...
94.1
v W§#~
V ~ffi
v t///~
vW#/~
~
~
17 [/
[/ ~~
~ ~
v W~
v~//~
~
~
~c.: l/
94
~
/ 8//#/~
~/ffi0.
[/ ~
~#//;
~~
~~
93 .9
~///;
/, ~
~~
93.8
93.7
500 600 700
800
900 10010 1100
1013 /691..57
atmospheric pressure [m bar]
Fig. 3:2. Sound level depending on the Atmosphere pressure.
Sound level
[dB]
±0.25dB
±0.35dB
0/50° ± O.SOdB
94.6 +----+---+-----+----+------1
94
93.4 ~----~----~------~----~------+--+
0
10 20 30 40 50
/691.56
ambient temperature [oc]
Fig. 3. 3. Sound pressure level.
9

for up to one minute (with a new battery) after the pushbutton is released,
thus leaving one hand free for adjustment of the sound measuring instru-
ment. The hold
circuit is also used as an indication of battery wear.
The mode
of operation is shown in Fig.3.1.
1Q

4. Further calibration
The Sound Level Calibrator Type 4230 is made for field calibration of
sound measuring systems. For complete calibration of condenser micro-
phones
with regard to sensitivity and frequency response, use should be
made of the B & K Microphone Calibration Apparatus Type 4142 (Fig.4.).
This includes equipment
for reciprocity calibration to a very high accuracy,
and electrostatic actuators
for precise determination of microphone fre-
quency response.
Fig.
4.
•
--
~ '
~til~~~
f:pflq
Microphone Calibrating Apparature 4142.
11

5.
Frequency:
Sound pressure level:
Accuracy:
Influence of static pressure:
Distortion:
Microphone types:
Power Supply:
Battery check:
Specifications
1000Hz ±1.5%
94 dB
re 2x1Q-5 N/m2 (1 N/m2)
±0.25 dB at 250C
±0.35 dB between.1 ooc and 4QOC
±0.50 dB between ooc and 5QOC
±0.05 dB per 100 mbar change in
pressure between 500 mbar and 1100 mbar
Less than 1%
1 in and 1/2 in
Built-in battery 1 x
9V (IEC 6 F 22,
NEDA 1604)
As long as the signal lasts for a few
seconds the change in SPL is less
than 0.05 dB.
Dimensions including leather
case: Length 110mm
Weight:
Temperature range:
Equivalent volume:
Accessories:
12
Diameter 44 mm
260g.
0- 5QOC
lVI> 200 cm3 at 250C
lV I> 100 cm3 between 1QOC and 4QOC
l VI > 50 cm3 between ooc and5QOC
1 Battery
1 leather
case
1 adaptor

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'B K
ORBOE PRINT . COPENHAGEN . DENMARK
August 1969