BRUEL & KJAER 2204 User guide

Impulse Precision Sound
Level Meter Type 2204
A compact and portable instrument
for precision sound and vibration
measurements. It conforms to
IEC 179 for Precision Sound Level
Meters, the proposed IEC
Recommendation for Impulse
Precision Sound Level Meters and
to DIN
45 633 parts 1 and 2.

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Precision Sound Level Meter
Type 2203/1613
Reprint may 1970

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Contents
1. General
5
2. Sound Level Meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Technical Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Condenser Microphone and Cathode Follower . . . . . . . . . . . . . . . . . . . . . . 13
Input Amplifier ..........................•....................... 14
Weighting Network .............................................. 14
Output Amplifiers and Attenuators ................................ 14
Rectifier and Indicating Meter .................................... 14
Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3. Filter Set Type 1613 .............................................. 15
Filter Characteristics ............................................ 16
Weighting Potentiometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Sound Level Meter .............................................•. 19 ·
Octave Filter Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Calibration Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Measurement of Sound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Measurement of Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . •. . . . . . . •. . . . . . . . . 24
Specifications for Integrator ZR 0020 ........................... :. . 25
Use of External Filters ........................................... 26
5. Accuracy of Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Condenser Microphone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Meter ................•..............•........................... 28
Calibration Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . •. . . . . 29
Power Supply . . . •. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . •. . . . . . . •••. . . 29
Weighting Network .............................................. 30
Effects of Vibration and Sound .............................•..•. 33
Effects of Electric and Magnetic Fields . . . . . . . . . . . . .. •. . . . . . . • . . •• . 34
Distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Inherent Noise Levels ..................................... . ...... 37
6. Operating Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Directional Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Notes on Reflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . •. . . . . . . . . 40
Influence of Background Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

7. Methods of Calibration
Noise Source Type 42·40
Pistonphone Type 4220
.........•..••.....•.......••.••••........ 45
45
•.•....................................... 46
Sound Level Calibrator 4230 ...................................... 47
8. Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
9. Applications ..................................................... 57
Noise ........................................................... 58
Vibration . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Frequency Response of 4-pole Networks .......................... 59
Tape Recording of Sound and Vibration Data . . . . . . . . . . . . . . . . . . . . . . 59
Frequency Response and Directivity Pattern of Loudspeakers . . . . . . 61
Satistical Distribution of Sound Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Sound and Vibration Spectrograms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
10. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
11.
Specifications ................................................... 65

1. General
Vibration and Sound.
It is generally known that sound is a transmission of energy through solid,
liquid br gaseous media in the form of vibrations. These vibrations con·
stitute variations in pressure or position of the particles in the medium.
Sound may also be defined as the auditory sensation evoked when such
vibrations, normally in air, impinge upon the ear. As an auditory sensation
sound is limited to frequencies in the range from about 20 Hz to 20ooo Hz.
Pressure fluctuations outside this range will not generally produce the
sensation of sound .
The Decibel Seale.
Acoustical instruments for measuring pressure variations are usually
calibrated in dB (decibel). A dB value is a measure of relative power, i.e.
so
many dB above a reference power level:-
p
dB= 10 log -
Po
where Po is the reference and P is the actual power measured. However,
the power transmitted by a sound wave is proportional to the square of the
pressure variations so that we have
p2 p
dB= 10log
2 = 20
log -
Po po
where po is the reference pressure and p is the root mean square value
of the pressure variations. When sound pressure is measured in dB re
o.0002 ,ubar with equal weight given to all frequencies it is termed
sound pressure level.
fhe logarithmic scale has been found very convenient because of the large
range of sound intensities that the human ear can handle. It can detect
pressure variations as low as o.0002 pbar and can also withstand levels
higher than 200 pbar. This is a ratio of more than 106: 1 which on the
logarithmic scale is represented by 120 dB .
In Table 1.1 are given some commonly encountered sound pressure levels in
order to give a better appreciation of the dB scale.
5

Sound pressure
in bar
mbar
10
,ubar
1
.ubar
o.1
,ubar
o.01
pbar
0.001
,ubar
0.0002
.ubar
Sound level in dB
I
Environmental conditions
1134 dB
-114 dB
94 dB
74 dB
T 54 dB
I
l 34 dB
I 14 dB
I
1
140
130
120
110
I
T Threshold of pain
T Pneumatic Chipper
T Loud automobile horn (dist. 1m)
Tlnside airliner (DC 6)
-,Inside subway train (New York)
90
-, Inside motor bus
80
100
-, Average traffic on street corner
70
-,Conversational speech
60
-, Typical business office
50
-, Living room, suburban area
40
-,Library -
30
-, Bedroom at night
20
-, Broadcasting studio
10
0 I
Threshold of hearing
I
Table 1.1. Some commonly encountered sound pressure levels.
The Detection of Sound.
The human ear is a remarkably sensitive instrument for the detection of
sound waves. Its response to a certain sound pressure level depends however
upon the frequency of the sound. The sensitivity is greatest at 1ooo-6ooo Hz
and falls off both for higher and lower frequencies.
6

A set of so-called equal loudness contours is given in Fig. 1.2. The curves
show the intensity levels in dB re o.0002 ~-tbar, which at various frequencies
are judged by the average human to sound equally loud. Other sets of
equal loudness contours which deviate from these curves in certain respects
have been published by various investigators but the curves shown in
Fig. 1.2 have been recommended as standard by the International Organiza-
tion for Standardization (ISO/R 226-1961 (E)).
140
N-
1 "-..
-
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E
z-
130
•a
X 120
N
N "
r--.
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-
130,
"""
I
' -
1--
.......__
~""'---
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. '\..
I'-. r-.
120-..... .......
-./
E
1
110
N 100
a
a
l\. "
--
""'
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I"
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110-.....r......
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---
1'---
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r-.....
100-
r-......
;-
C)
a 90
C1J
>
0
..c
80
0
I \. l\. !"----
90
1'---
I/ "
l '\ r'-.
'
--
--
.............
;-
l'\
...............
80
........
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l '\
'
1--
-r--
--
--
'\..../
C1J
70
..c
u 1'\
...............
........
'\
\ '
1--
r-
-70
-- ......
'\../
C1J
"0
60
c \
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'
.................
'r- v '\
,\
1'---.
--
60
- ...........
v
"0
C1J
50
VI
VI
QJ
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1-- :--.........
50 1'--- I/
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'
~
--
- ...........
'-"
a.
40X
C1J
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1'---
...........
40
t--
v 'l\. I
'
........
-/
~
30
r---
..............
I'-
30
r-r-
v
'V.
f'.-.
"'-........
--
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[ 20
"0
10
c
::;J
0
Ill
I
', ...... , ...... _ 20 r- v
'-"
I '
r-
---
-
V.'
Normal Binaural '
-r- 1'--
v~
',_,
I
--Minimum
Audible
10 -I
--Field
(MAF)
-
...........
I
Phon
-- r-
II II I ' --
I II II I
2,0 Hz 30 40 60 80 100 200 300 400 600 800 1000
~~Hz 3 6 8 10 15
Frequency f62381
Fig. 1.2. Equal loudneu contours.
The reference level is usually set up at looo Hz and the curves give the ·
sound pressure level in dB necessary for a tone of a different frequency
to sound equally loud. The loudness level is measured in phon and at
looo Hz the phon value is equal to the dB value. It will be seen that the ·
curves of constant phon become more and more straight as the loudness .
level
is increased. At a level of 120 phon the ear is approximately equally
sensitive to all frequencies in the audible range, while at 0 phon the ·
variation in sound pressure level with frequency is great.
Although the response of the human ear depends on many other things .
beside frequency, modern sound level meters usually contain weighting :
networks in order to try and incorporate in the meter a frequency response ·
similar to that of the human ear. Three different curves have been inter-
7

nationally agreed upon and standardized. These are referred to as the
A, B and C curves and are shown in Fig. 1.3. When sound pressure is
measured using one of the weighting networks and quoted in dB re o.0002
.ubar
it is tenned sound level. The weighting network used should always be
stated clearly e.g. if the sound level measured with the A weighting network
is 70 dB, it should be quoted as 70 dB' (A).
d
8
-b
o~
..-
~
~
~ ......
~ ~
~
0~
~
s>
~
A/~
Cl+~
0
~
nv
II
-
v~
.
0 I
01
-1
-2
-3
-I.
-5
-6
0 2 5
102
2
103
2 Hz 5 10' >
16f~9f
Fig. 1.l. Graph showing the response of the built-in weighting networks.
The Deteetlon of VIbration.
A phenomenon which is closely related to what we usually think of as
sound is vibrations in solid materials. Such vibrations are in most cases
the source of sound and may have to be located in order to reduce their
effect. (Noise control). Man's sensitivity to vibration is extremely limited,
especially for the higher frequencies, so that measuring instruments are
needed in order to detennine accurately the vibrations in question. By
substituting an accelerometer for the microphone, a sound level meter can
usually be adapted to measure vibration instead of . sound level and thus
serve a dual purpose in the fight against excessive noise.
Noise and VIbration Analysis.
When measuring sound and vibration, more information can be gained if
bandpass filters are used in connection with the sound level meter. It is
then possible to determine a magnitude versus frequency relation for the
sound or vibration in question. This is of great value in noise rating and
especially in noise control, as the knowledge of the frequency of a sound
often determines the method used for reducing it. Knowing the frequenc)
of vibration on some industrial machinery can also be very helpful in
localizing the source of this vibration.
Good sound level meters therefore have means for connecting external filters
for frequency analysis of the incoming signal.
8