BRUEL & KJAER 4204 User manual

Technical
Documentation
HEADQUARTERS: Brüel&Kjær Sound & Vibration Measurement A/S · DK-2850 Nærum · Denmark
Telephone: [phone] · Fax: [phone] · www.bksv.com · [e-mail]
Local representatives and service organisations worldwide
Reference Sound Source Type 4204
English BE0105–15
User Manual
ËBE-0105---bÎ

BE0105−15 April 2013
Reference Sound Source
Type 4204
User Manual

Copyright 2013, Brüel&Kjær Sound & Vibration Measurement A/S
All rights reserved. No part of this publication may be reproduced or distributed in any form, or
by any means, without prior written consent from Brüel & Kjær Sound & Vibration Measurement
A/S, Nærum, Denmark
Safety Considerations
This apparatus has been designed and tested in accordance with IEC/EN 61010 – 1 and
ANSI/UL 61010 – 1 Safety Requirements for Electrical Equipment for Measurement,
Control and Laboratory Use. This manual contains information and warnings which must be
followed to ensure safe operation and to retain the apparatus in safe condition. Special note should
be made of the following:
Safety Symbols
The apparatus will be marked with this symbol when it is important that you refer to the
associated warning statements given in the manual.
Protective Earth Terminal Hazardous Voltage
Explosion Hazard
The equipment is not designed to be used in potentially explosive environments. It should not be
operated in the presence of flammable liquids or gases.
Warnings
• Switch off all power to equipment before connecting or disconnecting their digital interface.
Failure to do so could damage the equipment
• Whenever it is likely that the correct function or operating safety of the apparatus has been
impaired, it must be made inoperative and be secured against unintended operation
• Any adjustment, maintenance and repair of the open apparatus under voltage must be
avoided as far as possible and, if unavoidable, must be carried out only by trained service
personnel
• Do not dispose of electronic equipment or batteries as unsorted municipal waste
• It is your responsibility to contribute to a clean and healthy environment by using
the appropriate local return and collection systems
• Hazardous substances in electronic equipment or batteries may have detrimental
effects on the environment and human health
• The symbol shown to the left indicates that separate collection systems must be used
for any discarded equipment or batteries marked with that symbol
• Waste electrical and electronic equipment or batteries may be returned to your
local Brüel & Kjær representative or to Brüel & Kjær Headquarters for disposal

Contents
CHAPTER 1
Introduction......................................................................................................... 1
1.1 About This Manual............................................................................................... 1
1.2 Reference Sound Source Type 4204................................................................... 1
CHAPTER 2
Operation............................................................................................................. 5
2.1 Connection of Mains Supply................................................................................ 5
2.2 Sound Power Measurements............................................................................... 6
2.3 Sound Absorption Measurements...................................................................... 12
2.4 Sound Insulation Measurements ....................................................................... 13
CHAPTER 3
Characteristics.................................................................................................. 17
3.1 Frequency Characteristics................................................................................. 17
3.2 Factory Calibration............................................................................................. 18
3.3 Directional Characteristics................................................................................. 18
3.4 Influence of Rotational Speed............................................................................ 20
3.5 Acoustical Effect of Barometric Pressure........................................................... 22
3.6 Acoustical Effect of Ambient Temperature......................................................... 23
3.7 Field Calibration................................................................................................. 23
3.8 Influence of Reflecting Plane............................................................................. 25
3.9 Influence of The Environment............................................................................ 25
3.10 Carrying Case WE-0268.................................................................................... 27
3.11 Service and Repair ............................................................................................ 27
CHAPTER 4
Specifications................................................................................................... 29
INDEX................................................................................................................... 33

1
Chapter 1
Introduction
1.1 About This Manual
This manual describes Reference Sound Source Type 4204, provides setup, input/output
connection, and basic measurement start-up instructions and power options. The aim is to
enable you to get familiar with the system, while preparing it for use.
Fig.1.1
Reference Sound Source
Type 4204
1.2 Reference Sound Source Type 4204
Reference Sound Source Type 4204 is a calibrated source of sound power with very well
defined operating characteristics and a predictable performance. It is rugged, compact and
stable, and is therefore suitable for both field and laboratory use.
Type 4204 is intended for use as a reference sound source for determination of the sound power
output of equipment by the various comparison methods, including the method described in
ISO 3741, and by the survey methods described in ISO 3747.
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Reference Sound Source Type 4204 — User Manual2
Type 4204 is also used for measuring environmental correction K2when determining sound
power according to ISO 3744. It is also useful in the field of building acoustics to determine the
sound absorption and sound insulation of a room.
The reference sound source consists essentially of a specially designed centrifugal fan driven
by a powerful asynchronous motor. The motor is an external rotor type, and due to its high
moment of inertia, it has a very constant speed of rotation. The motor is mounted on a cast
aluminium base, shaped to minimize reflections. The complete assembly of motor and fan is
within a cylindrical safety grid fitted with two carrying handles.
The directional characteristic of the reference sound source in the vertical plane varies less than
6 dB for any frequency in the range 100 Hz to 10 kHz (measured in 1/3-octaves) – see
section 3.3. In the horizontal plane, the variation is less than 0.2 dB for frequencies up to
10 kHz (measured in 1/3-octaves). The reference sound source fulfils the requirements for
reference sound sources as stated in ISO 3741, ISO 3747, ISO 6926 and ANSI S12.5. The use
of a reference sound source in noise and sound power measurements on machines is also
described in DIN 45635.
The reference sound source has a frequency range of 100 Hz to 20 kHz. In the range from
100 Hz to 10 kHz, the acoustic power output is greater than 70 dB re 1 pW in any 1/3-octave
frequency band. The A-weighted output is typically 91 dB (50 Hz line frequency) and 95 dB
(60 Hz line frequency). Fig.1.2 shows a typical 1/3-octave frequency response curve of the
Type 4204.
Fig.1.2 Typical sound power spectrum of the Type 4204
901108/1
Sound Power Level of 4204 (dB re 1 pW)
80
100 200 500 1k 2k 5k 10k 20k
75
70
85
Frequency (Hz)
A-weighted level for
60 Hz line freq. and
115 V line volt = 96.0 dBA
A-weighted level for
50 Hz line freq. and
220 V line volt = 91.7 dBA

CHAPTER 1
Introduction 3
Each reference sound source is individually calibrated and, as standard, a calibration certificate
is supplied showing the sound power output from 100 Hz to 20 kHz at 230 V/50 Hz and
115 V/60 Hz operating voltages. Temperature, barometric pressure, humidity and rotational
speed are all given on the calibration certificate. The maximum interval between successive
calibration is 24 months. If there are signs of physical damage to Type 4204, then a
recalibration is recommended.
In the field, the sound power produced may differ from the calibrated value. Changes in mains
supply line voltage and frequency, ambient pressure, and temperature all affect the rotational
speed of Type 4204. In addition, changes in ambient pressure and temperature alter the specific
acoustic impedance of the air, also changing the sound power. Once the values are measured,
however, simple formulae can be used to calculate the correct sound power levels from the
values given on the calibration certificate.

Reference Sound Source Type 4204 — User Manual4

5
Chapter 2
Operation
2.1 Connection of Mains Supply
Before connecting a mains supply, the following checks and adjustments should be carried out to
ensure safe operation of the instrument.
2.1.1 Main Voltage Settings
Type 4204 operates from either a 50 Hz or a 60 Hz mains supply of 100, 115, 127, 220 or 240 V
AC. The influence of mains voltage variations is discussed in section 3.4. The fuse and voltage
selector are located on the bottom panel of the instrument. If the position of the voltage selector does
not correspond to the local voltage, remove the central fuse using a small screwdriver and turn the
voltage selector to the required position using a wide-blade screwdriver or a small coin.
2.1.2 Mains Fuse Rating
The fuse holder in the centre of the voltage selector contains the mains fuse, which may be released
using a small screwdriver. For operation from 100 to 127 V supplies, the fuse should be a 12.5 A
slow blow (Brüel & Kjær part VF-0043), whilst for 200 to 240 V supplies it should be 6.3 A slow
blow (Brüel & Kjær part VF-0044). Make sure that only fuses of the required rate current and of the
specified type are used for replacement. The use of mended fuses or the short-circuiting of fuse
holders should be avoided.
2.1.3 Mains Cable Connections
Type 4204 is equipped with an integral mains cable. Once the mains voltage setting and fuse have
been checked, a mains plug compatible with the local regulations and fittings may be connected to
the live (brown) and neutral (blue) conductors of the mains input cable. For maximum operating
safety the protective (green/yellow) conductor of the mains cable should be connected to a suitable
earth, such as the protective earth contact of a mains socket outlet. The use of extension cables
without a protective conductor should be avoided.
In countries where use of mains socket outlets without protective conductor is standard, the mains
supply should incorporate an authorized earth leakage current circuit breaker.
Type 4204 can now be connected to the mains supply and started by setting the Power switch to On.

Reference Sound Source Type 4204 – User Manual6
2.2 Sound Power Measurements
2.2.1 Principle
The use of a reference sound source is described as an alternative to direct sound power
measurements in several standards such as ISO 3741 and ASHRAE 36-72.
The method applies to reverberant or semi-reverberant sound fields and allows sound power
measurements to be performed without measuring the reverberation time, which is needed in
the direct method.
The reference sound source method only requires that the sound pressure levels produced by
the device under test and the reference sound source be measured. The sound power level of
the device under test is then determined from:
Lw= Lwr + Lp– Lpr (2.1)
where:
Lw= sound power level of the device under test (dB re 1 pW)
Lwr = sound power level of Type 4204 (dB re 1 pW)
Lp= sound pressure level of the device under test (dB re 20 µPa)
Lpr = sound pressure level of Type 4204 (dB re 20 µPa)
Measurements are normally carried out in 1/3-octave or octave bands. The corresponding
sound power level for the reference sound source is read from the calibration certificate which
is delivered with the instrument. A typical calibration certificate is shown in Fig.2.1 and details
on the calibration procedure are given in section 3.2. Care should be taken to select the column
corresponding to the appropriate mains frequency (50 Hz or 60 Hz). Actual field sound power
levels are determined from the calibration certificate with appropriate correction factors as
described in Chapter 3.
The standards and codes of practice normally require that measurements are made for several
microphone positions. As the sound field should be diffuse, measurements may be made along
various paths (a line, an arc, a circle, etc.) when using a traversed microphone mounted for
example on Rotating Microphone Boom Type 3923. When fixed microphones are used, a
minimum of three microphone positions is required, as specified by ISO 3741. The
microphone outputs should be scanned automatically and/or averaged on a mean square basis
before they are entered in eq. (2.1). This is done according to the formula:
(2.2)
where:
L= average sound pressure level (dB re 20 µPa)
Li= sound pressure level measured at point i(dB re 20 µPa)
n = number of measuring points
L10log10
1
n
---10Li10⁄
i1=
n





=

CHAPTER 2
Operation 7
Fig.2.1 Typical Calibration Certificate for Reference Sound Source Type 4204 (three pages)
120562

Reference Sound Source Type 4204 – User Manual8
120563

CHAPTER 2
Operation 9
120564

Reference Sound Source Type 4204 – User Manual10
A measuring system for automatic sound power determination is shown in Fig.2.2. This is a
recommended system for measurements to the following standards:
ISO 3741: Determination of sound power levels of noise sources Precision methods for broad-
band sources in a reverberation room.
ASHRAE 36-72: Measurement of sound power radiated from heating, refrigerating and air-
conditioning equipment.
Fig.2.2
Example of a sound
power measurement
arrangement in a
reverberant room using a
PULSE-based analysis
system
2.2.2 Measurement Methods
The choice of the measurement method depends upon whether it is possible to move the device
to be tested. If the machine is movable, the Substitution Method (see section 2.2.3) should be
used. If this is not the case, a location similar to that of the machine should be found for the
reference sound source and the Comparison Method used (see section 2.2.4). Finally, if the two
above methods cannot be used, measurements should be made according to the Juxtaposition
Method (see section 2.2.5).
2.2.3 Substitution Method
This method should be used whenever possible. The room to be used must provide a semi-
reverberant or diffuse field. The qualification criteria for the room can be found in the relevant
standards. Details of the exact measuring procedure (number and position of measurement
points, test conditions, etc.) are also found in the standards.
Place the device in the room and measure the sound pressure level in each frequency band of
interest. Remove the machine and place the reference sound source in the same position in the
room and repeat the same set of measurements.
After averaging the band sound pressure level in space and time, the sound power level may be
determined from eq. (2.1).
4204 Reference
Sound Source
3923 Rotating
Microphone Boom
PC
PULSE software
3160-A
PULSE
LAN XI
Reverberant Room
120557

CHAPTER 2
Operation 11
2.2.4 Comparison Method
This method applies when it is not possible to move the machine, but when a similar location
may be found for Type 4204. This requires a diffuse sound field in the part of the room where
the sound pressure measurement is to be performed. A method for checking whether the sound
field is diffuse is normally given in the standards. If this is the case, sound pressure level
measurements may be carried out on the machine as in section 2.2.3.
Most standards and codes of practice give tables where the correction factor may be found as a
function of the difference between the levels measured with and without the machine in
operation. The minimum difference below which no data should be reported is normally also
specified. (In the case of ISO 3741 this is 6 dB). The correction factors K(to be subtracted
from the measured sound pressure level) and minimum differences specified by ISO 3741 and
ASHRAE 36-72 are given as an example in Table 2.1.
The reference sound source should then be placed in a location similar to that of the machine as
far as reflections, etc., are concerned. With Type 4204 operating and the machine stopped, the
sound pressure level of Type 4204 may be measured and the sound power level of the machine
derived from eq. (2.1).
Again, the required number and position of the measuring points, test conditions, etc., are
stated in the relevant standard.
2.2.5 Juxtaposition Method
If it is not possible to use the substitution or comparison method, the juxtaposition method may
be used. Sound pressure level measurements are first carried out with the machine operating.
The machine is then stopped and Type 4204 is placed against or on the machine (several
positions for Type 4204 may be necessary when more than one sound source is identified in the
machine).
This method is not as accurate as the two previous methods and can only be used as an
approximate survey of the machine. One reason is, that the sound power output of the reference
source depends on the surroundings (see section 3.9).
The three methods have been described and compared to the direct measurement method in an
article entitled “The Use of a Reference Sound Source in Studying Industrial Noise”, by
P. Francois and D. de Montussaint, Inter-Noise 72 Proceedings, Washington D.C., October
4 – 6, 1972.

Reference Sound Source Type 4204 – User Manual12
2.2.6 Background Noise Corrections
When measurements are recorded in the presence of background noise, it may be necessary to
apply correction factors to the measured band sound pressure levels both for the device under
test and for Type 4204. For each frequency band, the background noise level should be
measured with neither the machine nor Type 4204 operating. Measurements should then be
carried out with the machine in operation, and finally with Type 4204 in operation.
Most standards and codes of practice give tables where the correction factor may be found as a
function of the difference between the levels measured with and without the machine in
operation. The minimum difference below which no data should be reported is normally also
specified. (In the case of ISO 3741, this is 6 dB.) The correction factors K(to be subtracted
from the measured sound pressure level) and minimum differences specified by ISO 3741 and
ASHRAE 36-72 are given as an example in Table 2.1.
2.3 Sound Absorption Measurements
The Reference Sound Source Type 4204 may be used for sound absorption measurements. The
reference sound source is activated in the test room and the sound pressure level Lp is
measured in the central part of the room. This is performed for each frequency band of interest.
The absorption of the room is given by:
(2.3)
where:
ρis the density of air
cis the sound velocity in air
WRis the sound power emitted from the reference sound source
is the mean of the sound pressure squared (averaged over the entire room)
Table 2.1.
Background noise
corrections as specified
by ISO 3741 and
ASHRAE 36-72.
Correction factor K to be
subtracted from
measured sound
pressure levels
ISO 3741 ASHRAE 36-72
Diff. (dB) K(dB) Diff. (dB) K(dB)
61.3
7 1.0 4 – 4.5 2
8 0.8 5 – 5.5 1.5
9 0.6 6 – 7.5 0.5
10 0.4 8–12 0.5
Minimum Difference: 6 dB Minimum Difference: 4 dB
A4ρcWR
p2
------------------
=
p2

CHAPTER 2
Operation 13
To obtain a logarithmic scale, the following reference values are introduced: p0= 20 µPa,
W0=10
–12 W and A0= 1 m2and eq. (2.3) becomes:
(2.4)
and setting ρcto 400 Nsm*:
(2.5)
Eq. (2.3) to (2.5) are only valid if the sound pressure squared is averaged over the entire room.
However, this averaging is normally only done over the central part of the room and to
compensate for that, the so-called Waterhouse correction is added. Introducing the Waterhouse
correction, eq. (2.5) becomes:
(2.6)
where:
λ= the wavelength at the centre frequency of the band
S= the surface area of the room
V= the volume of the room
2.4 Sound Insulation Measurements
The reference sound source may be used for power-based measurements of sound insulation.
To perform this, the alternative method, which is described in detail in the Technical Review
No.3, 1980, can be used. An updated measurement arrangement is shown in Fig.2.3.
*ρc = 414 Nsm–3 for an ambient pressure of 1013 hPa and an ambient temperature of 20°C. This results in
a constant of 6.2 instead of 6 in eq. (2.5).
10log10
A
A0
------10log10
WR
W0
--------10log10
–p2
p0
2
--------10log10
+
4ρcW0
A0p0
2
-----------------
=
10log10
A
A0
------LwLp
–6+=
10log10
A
A0
------LwLp
–10log10 1λS
8V
-------
+


–6+=

Reference Sound Source Type 4204 – User Manual14
Fig.2.3 Measuring arrangement for sound insulation measurements using a PULSE based
analysis system
In some cases, i.e., when a high sound insulation is present, the power output of Type 4204
might be too low for use as a sound source in the transmitting room. In such circumstances
another source could be used in the transmitting room and Type 4204 used as reference in the
receiving room.
The measurement procedure is as follows:
1) With the reference sound source (or any other source) switched on in the transmitting
room (A), the averaged sound pressure levels L1and L2in the transmitting and receiving
rooms (B) respectively are measured. If necessary, the levels are corrected for background
noise.
2) The reference sound source is placed in the receiving room, turned on and the averaged
sound pressure level L2Rin the receiving room is measured.
3) The transmission loss Rin direction A-B is calculated from:
(2.7)
Direction A B
→
Test Specimen
Area S
Transmitting Room
Volume V1Surface Area S1
Receiving Room
Volume V2Surface
Area S2
3923 Rotating
Microphone Boom
3923 Rotating
Microphone Boom
4166/2639
Microphone
Assembly
4166/2639
Microphone
Assembly
120556
PC
PULSE
software
3160-A PULSE LAN-XI
4204 Reference
Sound Source
4204 Reference
Sound Source
RL
110log10 1λS1
8V1
---------
+



L2
–10log10
S
S0
----- LWR
–L2R6–+++=