EN ISO 3743-2:2009

SLOVENSKI STANDARD
01-november-2009
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SIST EN ISO 3743-2:1997
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Acoustics - Determination of sound power levels of noise sources using sound pressure -
Engineering methods for small, movable sources in reverberant fields - Part 2: Methods
for special reverberation test rooms (ISO 3743-2:1994)
Akustik - Bestimmung der Schalleistungspegel von Geräuschquellen aus
Schalldruckmessungen - Verfahren der Genauigkeitsklasse 2 für kleine, transportable
Quellen in Hallfeldern - Teil 2: Verfahren für Sonder-Hallräume (ISO 3743-2:1994)
Acoustique - Détermination des niveaux de puissance acoustique émis par les sources
de bruit à partir de la pression acoustique - Méthodes d'expertise en champ réverbéré
applicables aux petites sources transportables - Partie 2: Méthodes en salle d'essai
réverbérante spéciale (ISO 3743-2:1994)
Ta slovenski standard je istoveten z: EN ISO 3743-2:2009
ICS:
17.140.01 $NXVWLþQDPHUMHQMDLQ Acoustic measurements and
EODåHQMHKUXSDQDVSORãQR noise abatement in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 3743-2
NORME EUROPÉENNE
EUROPÄISCHE NORM
July 2009
ICS 17.140.01 Supersedes EN ISO 3743-2:1996
English Version
Acoustics - Determination of sound power levels of noise
sources using sound pressure - Engineering methods for small,
movable sources in reverberant fields - Part 2: Methods for
special reverberation test rooms (ISO 3743-2:1994)
Acoustique - Détermination des niveaux de puissance Akustik - Bestimmung der Schalleistungspegel von
acoustique émis par les sources de bruit à partir de la Geräuschquellen aus Schalldruckmessungen - Verfahren
pression acoustique - Méthodes d'expertise en champ der Genauigkeitsklasse 2 für kleine, transportable Quellen
réverbéré applicables aux petites sources transportables - in Hallfeldern - Teil 2: Verfahren für Sonder-Hallräume (ISO
Partie 2: Méthodes en salle d'essai réverbérante spéciale 3743-2:1994)
(ISO 3743-2:1994)
This European Standard was approved by CEN on 13 July 2009.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2009 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 3743-2:2009: E
worldwide for CEN national Members.

Contents Page
Foreword .3
Annex ZA (informative) Relationship between this European Standard and the Essential
Requirements of EU Directive 98/37/EC .4
Annex ZB (informative) Relationship between this European Standard and the Essential
Requirements of EU Directive 2006/42/EC .5

Foreword
The text of ISO 3743-2:1994 has been prepared by Technical Committee ISO/TC 43 “Acoustics” of the
International Organization for Standardization (ISO) and has been taken over as EN ISO 3743-2:2009 by
Technical Committee CEN/TC 211 “Acoustics” the secretariat of which is held by DS.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by January 2010, and conflicting national standards shall be withdrawn at
the latest by January 2010.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 3743-2:1996.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association, and supports essential requirements of EC Directives.
For relationship with EC Directives, see informative Annexes ZA and ZB, which are integral parts of this
document.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 3743-2:1994 has been approved by CEN as a EN ISO 3743-2:2009 without any modification.
Annex ZA
(informative)
Relationship between this European Standard and the Essential
Requirements of EU Directive 98/37/EC
This European Standard has been prepared under a mandate given to CEN by the European Commission
and the European Free Trade Association to provide a means of conforming to Essential Requirements of the
New Approach Directive 98/37/EC, amended by 98/79/EC on machinery.
Once this standard is cited in the Official Journal of the European Communities under that Directive and has
been implemented as a national standard in at least one Member State, compliance with the normative
clauses of this standard confers, within the limits of the scope of this standard, a presumption of conformity
with the relevant Essential Requirements of that Directive and associated EFTA regulations.
WARNING - Other requirements and other EU Directives may be applicable to the product(s) falling within the
scope of this standard.
Annex ZB
(informative)
Relationship between this European Standard and the Essential
Requirements of EU Directive 2006/42/EC
This European Standard has been prepared under a mandate given to CEN by the European Commission
and the European Free Trade Association to provide a means of conforming to Essential Requirements of the
New Approach Directive 2006/42/EC on machinery.
Once this standard is cited in the Official Journal of the European Communities under that Directive and has
been implemented as a national standard in at least one Member State, compliance with the normative
clauses of this standard confers, within the limits of the scope of this standard, a presumption of conformity
with the relevant Essential Requirements of that Directive and associated EFTA regulations.
WARNING — Other requirements and other EU Directives may be applicable to the product(s) falling within
the scope of this standard.
INTERNATIONAL
ISO
STANDARD
3743-2
First edition
1994-11-01
Acoustics - Determination of Sound
power levels of noise sources using Sound
- Engineering methods for
pressure
small, -movable sources in reverberant
fields -
Part 2:
Methods for special reverberation test rooms
Acoustique - Determination des niveaux de puissance acoustique 6mis
par les sources de bruit ~9 partir de Ia Pression acoustique - Methodes
d ’expertise en champ r&erb&6 applicables aux petites sources
transportables -
Partie 2: Methodes en salle d ’essai rkverbkan te spkciale
Reference number
ISO 37432:1994(E)
ISO 3743-2: 1994(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide
federation of national Standards bodies (ISO member bodies). The work
of preparing International Standards is normally carried out through ISO
technical committees. Esch member body interested in a subject for
which a technical committee has been established has the right to be re-
presented on that committee. International organizations, governmental
and non-governmental, in liaison with ISO, also take part in the work. ISO
collaborates closely with the International Electrotechnical Commission
(1 EC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard ISO 3743-2 was prepared by Technical Committee
lSO/TC 43, Acoustics, Subcommittee SC 1, Noise.
This first edition cancels and replaces the ISO 3743:1988, of which it
constitutes a minor revision.
ISO 3743 consists of the following Parts, under the general title
Acoustics - Determination of Sound power levels of noise sources using
Sound pressure - Engineering methods for small, movable sources in
reverberan t fields:
- Part 7: Comparison method for hard-walled test rooms
- Part 2: Methods for special reverberation test rooms
Annex A forms an integral patt of this part of ISO 3743. Annexes B, C and
D are for information only.
0 ISO 1994
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronie or mechanical, including photocopying and
microfilm, without Permission in writing from the publisher.
International Organization for Standardization
Gase Postale 56 l CH-l 211 Geneve 20 l Switzerland
Printed in Switzerland
0 ISO
ISO 3743-2: 1994(E)
0.1 ISO 3743 is one of the ISO 3740 series, which specifies various
methods for determining the Sound power Ievels of machines, equipment
and sub-assemblies. These basic Standards specify the acoustical re-
quirements for measurements appropriate for different test environments
as shown in table 0.1. When selecting one of the methods of the ISO 3740
series, it is necessary to select the most appropriate for the conditions and
purposes of the noise test. General guidelines to assist in the selection
are provided in ISO 3740. The ISO 3740 series gives only general prin-
ciples regarding the operating and mounting conditions of the machine or
equipment under test. Reference should be made to the noise test code
for a specific type of machine or equipment, if available, for specifications
on mounting and operating conditions.
0.2 The method given in this part of ISO 3743 enables measurement
of Sound pressure levels with A-weighting and in octave bands at pre-
scribed fixed microphone positions or along prescribed paths. lt allows
determination of A-weighted Sound power levels or Sound power levels
with other weighting and octave-band Sound power levels. Quantities
which cannot be determined are the directivity characteristics of the
Source and the temporal Pattern of noise radiated by sources emitting
non-steady noise.
0.3 Parts 1 and 2 of ISO 3743 specify engineering methods for deter-
mining the A-weighted and octave-band Sound power levels of small noise
sources. The methods are applicable to small machines, devices, com-
ponents and sub-assemblies which tan be installed in a special reverber-
ation test room or in a hard-walled test room with prescribed acoustical
characteristics. The methods are particularly suitable for small items of
portable equipment; they are not intended for larger pieces of stationary
equipment which, due to their manner of Operation or installation, cannot
readily be moved into the test room and operated as in normal usage. The
procedures are intended to be used when an engineering grade of accu-
racy is desired without requiring the use of laboratoty facilities.
0.4 In ISO 3743-1, a comparison method is used to determine the
octave-band Sound power levels of the Source. The spatial average
(octave-band) Sound pressure Ievels produced by the Source under test
are compared to the spatial average (octave-band) Sound pressure levels
produced by a reference Sound Source of known Sound power output. The
differente in Sound pressure levels is equal to the differente in Sound
power levels if conditions are the Same for both sets of measurements.
The A-weighted Sound power level is then calculated from the octave-
band Sound power levels.
. . .
Ill
ISO 3743-2: 1994( lg 0 ISO
The requirements to be fulfilled by the special reverberation test room for
measurements in accordance with this part of ISO 3743 are significantly
more restrictive than those placed on the hard-walled test room by the
comparison method of ISO 3743-1.

International
Classification of Sound power levels Optional information
Test environment Volume of Source Character of noise
Standard methodl) available
obtainable
Steady, broad-band
Reverberation room
Precision In one-third-octave A-weighted Sound
Steady, discrete fre-
meeting specified
(grade 1) or octave bands power ievel
quency or narrow-
requirements
Preferably less than
band
1 % of test room
Hard-walled test
volume
Steady, broad-band,
room
Engineering Other weighted Sound
A-weighted and in
narrow-band, or dis-
(grade 2) octave bands power ievels
Special reverber-
trete frequency
ation test room
Engineering Outdoors or in large Greatest dimension
Directivity information
AnY
(grade 2) room less than 15 m
A-weighted and in and Sound pressure
one-third-octave or leveis as a function of
Preferably less than
Precision Anechoic or semi-
time; other weighted
octave bands
3745 0,5 % of test room
AnY
(grade 1) anechoic room
Sound power levels
volume
Sound pressure levels
No restrictions: limi-
No special test en- as a function of time;
3746 Survey (grade 3) ted only by available A-weighted
AnY
vironment other weighted Sound
test environment
power levels
No special test en-
Steady, broad-band,
vironment; Source
Sound power levels in
3747 Survey (grade 3) No restrictions narrow-band, or dis- A-weighted
under test not mov- octave bands
trete frequency
able
1) See ISO 2204.
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INTERNATIONAL STANDARD 0 ISO ISO 3743=2:1994(E)
- Determination of Sound power levels of
Acoustics
noise sources using Sound pressure - Engineering
methods for small, movable sources in reverberant
fields -
Part 2:
Methods for special reverberation test rooms
the requirements on the test room for the comparison
1 Scope
method of ISO 3743-1 are considerably less restric-
tive, it is recommended that the comparison method
1.1 General
of ISO 3743-1 be used if a special reverberation test
room is not available.
This patt of ISO 3743 specifies a relatively simple en-
gineering method for determining the Sound power
NOTE 1 Precision methods for the determination of the
levels of small, movable noise sources. The
Sound power levels of small noise sources are specified in
ISO 3741 and ISO 3745.
measurements are carried out when the Source is in-
stalled in a specially designed room having a specified
reverberation time over the frequency range of
interest. The A-weighted Sound power level of the 1.2 Types of noise
Source under test is determined from a Single A-
The methods specified in this part of ISO 3743 are
weighted Sound pressure level measurement at each
suitable for measurements of all types of noise within
microphone Position, rather than from a summation
a specified frequency range, except impulsive noise
of octave-band Ievels. This direct method eliminates
consisting of isolated bursts of Sound energy.
the need for a reference Sound Source, but requires
the use of a special reverberation test room. The di-
NOTES
rect method is based on the premise that the Sound
pressure level, averaged in space and time in the test
2 A classification of different types of noise is given in
room, tan be used to determine the Sound power
ISO 12001.
level emitted by the Source. The properties of the
special reverberation test room are Chosen so that the 3 For sources of impulsive noise consisting of short-
duration noise bursts, the free-field methods specified in
room ’s influence on the Sound power output of the
ISO 3744 and ISO 3745 should be used.
equipment under test is small. The number of micro-
phone positions and Source locations required in the
test room are specified. Guidelines for the design of
1.3 Noise Source
special reverberation rooms are given in annex B.
On addition to the direct method, a comparison The noise Source may be a device, machine, com-
ponent or sub-assembly.
method is also described (see 8.3). However, since

0 ISO
ISO 3743-2: 1994(E)
The maximum size of the Source under test and the confidence that it lies within the range + 1,960, of
-
lower limit of the frequency range for which the the measured value. For further examples, reference
may be made to the ISO 9296 and ISO 7574 series.
methods are applicable depend upon the size of the
room used for the acoustical measurements. The
volume of the noise sources should not exceed 1 %
of the volume of the special reverberation test room.
For the minimum test room volume of 70 m3, the re-
NOTES
commended maximum size of the Source is 0,7 m3.
4 The Standard deviations listed in table 1 are associated
Measurements on sources emitting discrete-
with the test conditions and procedures defined in this part
frequency components below 200 Hz are frequently
of ISO 3743, and not with the noise Source itself. They arise
difficult to make in such small rooms.
partly from variations between measurement laboratories in
the geometry of the test room, the acoustical properties of
the test room boundaries, background noise, the type and
calibration of instrumentation, and the reference Sound
1.4 Measurement uncettainty
Source. They are also due to variations in experimental
measurement techniques, including microphone placement
Determinations made in accordance with this patt of
and spatial averaging, location of Source under test, inte-
ISO 3743 result, with few exceptions, in Standard
gration times, and measurement of reverberation time.
deviations of reproducibility equal to or less than
5 If several laboratories use similar facilities and instru-
2,0 dB from 500 Hz to 4 000 Hz, 3,0 dB for 250 Hz
mentation, the results of Sound power determinations on a
and 8 000 Hz, and 5,0 dB for 125 Hz (see table 1).
given Source in those laboratories may be in better agree-
ment than would be implied by the Standard deviations
A Single value of the Sound power level of a noise
given in table 1.
Source determined according to the procedures of
this part of ISO 3743 is likely to differ from the true
6 For a particular family of Sound sources, of similar size
value by an amount within the range of the measure-
with similar Sound power spectra and similar operating
ment uncertainty. The uncertainty in determinations
conditions, the Standard deviations of reproducibility may
of the Sound power level arises from several factors
be smaller than the values given in table 1. l-lence, a noise
which affect the results, some associated with en- test code for a particular type of machinery or equipment
making reference to this part of ISO 3743 may state stan-
vironmental conditions in the measurement laboratory
dard deviations smaller than those listed in table 1 if sub-
and others with experimental techniques.
stantiation is available from the results of suitable
interlaboratory tests.
If a particular noise Source were to be transported to
each of a number of different laboratories, and if, at
7 The Standard deviations of reproducibility, as tabulated
each laboratory, the Sound power level of that Source
in table 1, include the uncertainty associated with repeated
were to be determined in accordance with this patt
measurements on the same noise Source under the same
of ISO 3743, the results would show a scatter. The
conditions (for Standard deviation of repeatability, see
Standard deviation of the measured levels could be
ISO 7574-1). This uncertainty is usually much smaller than
calculated (see examples in ISO 7574-4: 1985, the uncertainty associated with interlaboratory variability.
However, if it is difficult to maintain stable operating or
annex B) and would vary with frequency. With few
mounting conditions for a particular Source, the Standard
exceptions, these Standard deviations would not ex-
deviation of repeatability may not be small compared with
ceed those listed in table 1. The values given in
the values given in table 1. In such cases, the fact that it
table 1 are Standard deviations of reproducibility, aR,
was difficult to obtain repeatable Sound power level data on
as defined in ISO 7574-1. The values of table 1 take
the Source should be recorded and stated in the test report.
into account the cumulative effects of measurement
uncertainty in applying the procedures of this part of
8 The procedures of this part of ISO 3743 and the stan-
ISO 3743, but exclude variations in the Sound power
dard deviations given in table 1 are applicable to measure-
ments on an individual machine. Characterization of the
output caused by changes in operating conditions
Sound power levels of batches of machines of the same
(e.g. rotational Speed, line voltage) or mounting con-
family or type involves the use of random sampling tech-
ditions.
niques in which confidence intervals are specified, and the
results are expressed in terms of statistical upper limits. In
The measurement uncertainty depends on the stan-
applying these techniques, the total Standard deviation must
dard deviation of reproducibility tabulated in table 1
be known or estimated, including the Standard deviation of
and on the degree of confidence that is desired. As
production, as defined in ISO 7574-1, which is a measure
examples, for a normal distribution of Sound power
of the Variation in Sound power output between individual
levels, there is a 90 % confidence that the true value
machines within the batch. Statistical methods for the
of the Sound power level of a Source lies within the
characterization of batches of machines are described in
range + 1,645~~ of the measured value and a 95 %
ISO 7574-4.
0 ISO
ISO 3743-2: 1994(E)
ISO 7574-4:1985, Acoustics - Statistical methods for
determining and verifying sta ted noise emission val-
Table 1 - Estimated values of the Standard
ues of machinery and equipment - Part 4: Methods
deviation of reproducibility of Sound power levels
for stated values for batches of machines.
determined according to this part of ISO 3743
Octave-band centre Standard deviation of
I EC 225: 1966, Octave, half-octave and third-octave
frequency reproducibility, aR
band filters intended for the analysis of Sounds and
Hz dB
vibra tions.
IEC 651 :1979, Sound level meters.
3,O
I EC 804: 1985, Integrating-averaging Sound level
500to4 000
me ters.
8 000
3,O
I EC 942: 1988, Sound calibrators.
2 0')
A-weighted l
1) Applicable to a Source which emits noise with a
3 Definitions
relatively “flat” spectrum in the frequency range
100 Hz to IO 000 Hz.
For the purposes of this part of ISO 3743, the defi-
nitions given in ISO 3743-1 and the following defi-
nition apply.
2 Normative references
3.1 special reverberation test room: A test room
meeting the requirements of this patt of ISO 3743.
The following Standards contain provisions which,
through reference in this text, constitute provisions
4 Requirements for special
of this part of ISO 3743. At the time of publication, the
editions indicated were valid. All Standards are subject
reverberation test room
to revision, and Parties to agreements based on this
part of ISO 3743 are encouraged to investigate the
4.1 General
possibility of applying the most recent editions of the
Standards indicated below. Members of IEC and ISO
Guidelines for the design of a suitable test room and
maintain registers of currently valid International
an example of the determination of the nominal re-
Standards.
Verberation time of the room are given in annex B.
Methods of measurement of reverberation time are
ISO 3741:1988, Acoustics - Determination of Sound
given in ISO 354.
power levels of noise sources - Precision methods
for broad-band sources in reverbera tion rooms.
4.2 Volume of test room
ISO 3743-1:1994, Acoustics - Determination of
The volume of the test room shall be at least 70 m3
Sound power levels of noise sources - Engineering
and preferably greater if the 125 Hz octave band is
methods for small, movable sources in reverberant
within the frequency range of interest. If the 4 kHz
fields - Part 1: Comparison me thod for hard-walled
and 8 kHz octave bands are within the frequency
test rooms.
range of interest, the volume shall not exceed
300 m3.
ISO 3745:1977, Acoustics - Determination of Sound
power levels of noise sources - Precision methods
NOTE 9 When using the comparison method, the use of
for anechoic and semi-anechoic rooms.
larger room volumes is acceptable.
ISO 6926:1990, Acoustics - Determination of Sound
power levels of noise sources - Requirements for 43 . Reverberation time of test room
the Performance and calibration of reference Sound
The calculation of Sound power levels from measured
sources.
values of the Sound pressure levels requires a com-
ISO 7574-1: 1985, Acoustics - Statistical methods for pensation for the frequency-dependent concentration
determining and verifying sta ted noise emission val- of Sound energy near the Walls of the test room. To
ues of machinery and equipment - Part 1: General facilitate this compensation, the reverberation time
considera tions and definitions. should be slightly higher at low frequencies. The re-
0 ISO
ISO 3743-2: 1994(E)
Source has absorptive surfaces, the reverberation
Verberation time T of the test room shall fall within the
time T shall be measured with these items present.
limiting curves defined by T = 0,9 R Tnom and
where the reverberation Parameter, R, is
IJ R T ”,,,
given by
4.4 Surface treatment
R = 1 + 257/(f V ’j3)
The floor of the test room shall be reflective with an
where
absorption coefficient less than 0,06. Except for the
floor, none of the surfaces shall have absorptive
f is the frequency, in hertz;
properties significantly deviating from each other. For
each octave band within the frequency range of in-
V is the volume, in cubic metres.
terest, the mean value of the absorption coefficient
of each wall and of the ceiling shall be within 0,5 and
For frequencies above 6,3 kHz, constants 0,9 and IJ
1,5 times the mean value of the absorption coefficient
shall be replaced by 0,8 and 1,2, respectively. The
of the Walls and ceiling.
nominal reverberation time of the room, Tnom, is de-
termined by centring the measured values of T (nor-
malized to the reverberation time at 1 000 Hz) within
4.5 Criterion for background noise
the limiting curves specified above, and shall be be-
tween 0,5 s and 1,0 s (see annex B for an example).
At each microphone Position, the Sound pressure
For a room volume V of 70 m3, the value of R is de-
Ievels due to background noise shall be at least 4 dß
termined from figure 1.
and preferably more than IO dB below the A-
weighted Sound pressure Ievel or the band pressure
If, during the acoustical measurements, sound-
absorptive structures support the Source or if the levels produced by the Source.
I
1 I4
e
-
&
G 12 &
E
L
m
n
c 1
.-
G
G
L
: ’
Cs
0 0 1 1
100 125 160
100 125 160 200 200 250 315
250 315 400 400 sc- 500 630 800 1000
--- --- 1250 1600 2 000 2500
3150 4000 1
One-third-octave-band centre frequency, Hz
Figure 1 -
Values of R at the one-third-octave-bandl centre frequencies for V= 70 m3
0 ISO
ISO 374392:1994( E)
46 ” Criteria for temperature and humidity
Table 2 - Maximum permitted differentes
The air absorption in the reverberation room varies between octave-band power ievels sf broad-band
with temperature and humidity, particularly at fre- noise sources measured in accordance with 4.7 a)
quencies above 1 000 Hz. The temperature 0, in de-
Octave-band centre Differente in band power
grees Celsius, and the relative humidity (r.h.),
frequency levels
expressed as a percentage, shall be controlled during
Hz dß
the Sound pressure level measurements. The product
r.h. x (0 + 5 “C) 125
250 to 4 000
shall not differ by more than &- IO % from the value
8 000
of the product which prevailed during the measure-
ment of the reverberation time of the test room.
NOTE IO To keep the reverberation time within the
5 Instrumentation
specified limits at the highest frequencies, a reduction of
the air absorption is sometimes necessary. An increase in
the humidity (for example by using a smail humidifier) may
5.1 General
be benef icial.
The basic instrumentation consists of a microphone,
an amplifier with A-weighting network, a squaring and
averaging circuit and an indicating device. A set of
4.7 Evaluation of suitability of test room
octave-band filters is also required. These elements
may be separate instruments or they may be inte-
Before a test room is used for Sound power level. de-
grated into a complete unit, for example, a suitable
terminations, its suitability shall be evaluated using
Sound level meter. For requirements on Sound Level
the following procedure.
meters, see IEC 651 and IEC 804.
a) Step 1
The microphone shall, whenever possible, be physi-
cally separated from the rest of the instrumentation
Obtain a small broad-band reference Sound Source
with which it is connected by means of a cable.
which has been calibrated in accordance with
Examples of suitable instrumentation Systems are
ISO 3741, or by following the procedures de-
given in annex C.
scribed in ISO 6926 and ISO 3745.
b) Step 2
5.2 Microphone and its associated cable
In the special reverberation test room, determine
The microphone shall have a flat frequency response
the octave-band power levels of the same refer-
for randomly incident Sound over the frequency range
ence Sound Source under identical operating con-
of interest, as determined by the procedure given in
ditions in accordance with the procedure given in
56 . .
this part of ISO 3743.
NOTES
c) Step 3
? 1 This requirement is not normally met by the micro-
For each octave band within the frequency range
phone of a Sound level meter which is calibrated for free-
of interest, calculate the differente between the
field measurements.
Sound power Ievels obtained in this way.
12 If several microphones are used, it is desirable to avoid
the axis of each microphone being oriented in the same di-
d) Step 4
rection in space.
Compare these differentes with the vatues given
The frequency response and stability of the micro-
in table 2.
phone System shall not be adversely affected by the
If the differentes in octave-band power levels do cable connecting the microphone to the rest of the
not exceed those specified in table2, the room is instrumentation System. If the microphone is moved,
suitable for Sound power determinations of care shall be exercised to avoid introducing acoustical
broad-band noise sources in accordance with the or electricat noise that could interfere with the
procedures of this part of ISO 3743. measurements.

0 ISO
ISO 3743-2: 1994(E)
5.7 Calibration
5.3 Amplifier and weighting network
During each series of measurements, a Sound
The properties of the amplifier and the A-weighting
calibrator with an accuracy of rf: 0,3 dB (class 1 as
network shall comply with the requirements of
specified in IEC 942) shall be applied to the micro-
IEC 651.
phone to verify the calibration of the entire measuring
System at one or more frequencies over the fre-
quency range of interest.
5.4 Octave-band filters
The calibrator shall be checked annually to verify that
The octave-band filters shall comply with the require-
its output has not changed. In addition, an electrical
ments of IEC 225.
calibration of the instrumentation System over the
entire frequency range of interest shall be carried out
periodically, at intervals not exceeding 2 years.
5.5 Squaring and averaging circuits, and
indicating device 6 Installation and Operation of Source
under test
Squaring and averaging the microphone output volt-
age may be performed by analog or digital equipment
6.1 General
as described in annex C. In analog Systems, continu-
ous averaging is generally performed by an
The acoustical proper-Ges of the special reverberation
RC-smoothing network with a time constant TA. For
test room and the manner in which the Source is op-
these Systems, the time constant shall be at least
erated may have a significant influence on the Sound
0,5 s and such that the indicated fluctuations are less
power emitted by the Source.
than + 5 dß.
-
6.2 Source location
In digital Systems and in some analog Systems, true
integration over a fixed timelinterval (integration
Install the Source in the test room in one or more lo-
time Q) is employed. The integration time shall be at
cations as if it were being installed for normal usage.
least 1 s. The indication of the squaring and averaging
If no such location(s) tan be defined, place the Source
(integrating) circuits and indicating device shall be
on the floor of the test room with a minimum distance
within 3 % of the values.
of 1 m between any surface of the Source and the
nearest Wall.
The locatio n(s) of the Source in the test room shall be
5.6 Frequency response of the
descri bed i report.
n the test
instrumentation System
NOTE 13 The influence of the acoustical properties of the
The frequency response of the instrumentation cali-
room on the Sound power emitted by the Source depends
brated for randomly incident Sound shall be deter-
to some extent on the Position of the Source within the
mined in accordance with the procedure in IEC 651
room. The requirements on the test room (see clause 4)
with the tolerantes given in table3.
tend to decrease this influence. However, in some cases it
may be necessary or desirable to determine the Sound
power level of a Source in several locations in the test room
Table 3 - Relative tolerantes for the
(see 7.4) .
instrumentation System
6.3 Source mounting
Frequency Tolerante limits
Hz dB
In many cases, the Sound power emitted will depend
100t04000
upon the support or mounting conditions of the
Source under test. Whenever a typical condition of
5 000
mounting exists for the equipment under test, that
6 300
condition shall be used or simulated, if feasible.
8 000
lf a typical condition of mounting does not exist or
cannot be utilized for the test, take care to avoid
10 000
changes in the Sound output of the Source caused by
Adapted from IEC 651.
NOTE -
the mounting System employed for the test. Take

0 ISO
ISO 3743-2: 1994(E)
Steps to reduce any Sound radiation from the struc-
7 Measurements in test room
ture on which the equipment may be mounted.
7.1 General
Sources normally mounted through a window, wall
or ceiling shall be mounted through a wall or the ceil-
The calculation of the approximate Sound power level
ing of the test room.
of the Source is based on measured mean-Square
values of the Sound pressure averaged in time over
The mou ting CO nditions of the Source and its asso-
an appropriate number of positions within the test
ciated eq U ipment shall be described in the test report.
room.
NOTE 14 The use of resilient mounts or vibration-
Use a Single microphone moved from Position to
damping material on large surfaces used to support the
Position, an array of fixed microphones, or a micro-
equipment under test may be appropriate.
phone moving continuously over an appropriate path
in the test room.
6.4 Auxiliary equipment
7.2 Period of Observation
Take care to ensure that any electrical conduits, piping
or air ducts connected to the Source under test do not
The period of Observation shall be at least ten times
radiate significant amounts of Sound energy into the
the time constant TA. Average the results over this
test room. If practicable, locate all auxiliary equipment
period and record the mean value as the result of the
necessary for the Operation of the Source under test
measurement.
outside the test room and clear the test room of all
For instrumentation with RC-smoothing, do not Start
objects which may interfere with the measurements.
any Observation after any filter switching or disturb-
ante of the Sound field (including transfer of the
Operation of Source during the test microphone to a new fixed Position) until a “settling”
6.5
time of at least five times the time constant of the
During the measurements, use the operating condi- instrumentation has elapsed.
tions specified in the test Code, if any exists for the
lf integration over a fixed time interval, Zn, is used, the
particular type of machinery or equipment under test.
measurement at each fixed microphone Position shall
If there is no test Code, operate the Source, if poss-
be of at least 5 s duration (for example: if Zn = 1 s,
ible, in a manner which is typical of normal use. In
five readings shall be averaged on a mean-Square
such a case, one or more of the following operating
basis; if Zn = 5 s, the reading at the end of the interval
conditions shall be selected:
of 5 s shall be taken). If the microphone is moved
over a path, the total period of Observation shall be
a) device under specified load and operating condi-
at least 30 s for frequency bands centred on 160 Hz
tions;
and below (and for A-weighting), and at least 10 s for
frequency bands centred on 200 Hz or above.
b) device under full load Cif different from a) above];
c) device under no load (idling);
7.3 Microphone positions
d) device under operating conditions corresponding
No microphone Position shall be closer to the surface
to maximum Sound generation representative of
of the room than L/4, where A. is the wavelength of
normal use.
Sound corresponding to the centre frequency of the
lowest octave band in which measurements are
The method given in this part of ISO 3743 is applica-
made. The minimum distance, dmin, in metres, be-
ble for determining the Sound power level of the
tween any microphone Position and the surface of the
Source under any desired set of operating conditions
Source under test shall be
(i.e. temperature, humidity, device Speed, etc.). These
test conditions shall be selected beforehand and shall
d
min = 0,3 V1 ’3
be held constant during the test. The Source shall be
in the desired operating condition before any acous-
where V is the volume of the test
room, in cubic
tical measurements are made. metres.
The operating conditions of the Source during the The distance between any two microphone positions
acoustical measurements shall be described in the
shall be at least n/2, where A. is the wavelength of the
test report. Sound wave corresponding to the centre frequency
ISO 3743-2: 1994(E) 0 ISO
properties are influenced by the characteristics of the
of the lowest octave band in which measurements
test room and the Source (i.e. its directivity and the
are made.
spectrum of the emitted Sound).
For measurements with A-weighting, assume
c) Step 3
R. = 3,5 m.
Enter in table4 the value of SM, in decibels, deter-
mined from step 2 and select from the table a
7.4 Number of microphones and Source
suitable combination of the minimum number of
positions
microphone positions, Nm, and Source locations,
Ns, for each octave band and for A-weighting.
The number of microphone positions and Source lo-
These minimum numbers of positions shall be
cations necessary to obtain a specified precision of
used in Order to obtain the accuracy specified in
the Sound power levels depend on the properties of
table 1.
the Source and the test room. For each Source, the
minimum number of positions necessary to obtain
As SM has been determined from six measure-
Standard deviations which are equal to or less than
ments in each octave band and for A-weighting,
the values given in table 1 shall be determined by the
the minimum value of Nm will generally be 6. If
following procedure which shall be followed for each
several samples of the Same type of Sound
octave band of interest and for A-weighting.
Source are measured one after another in the
Same test room, smaller values of Nm may be
a) Step 1
Chosen for all but the first Sample when appropri-
ate. In these circumstances, the sources shall,
For a particular Source location, measure the
however, be identical not only in geometry but
Sound pressure levels at six microphone pos-
also as far as the spectrum of the emitted Sound
itions.
is concerned.
b) Step 2
Table 4 - Minimum number of Source
Calculate the estimated Standard deviation, SM, in
locations, Ns, for given numbers of microphone
decibels, of the measured Sound pressure Ievels
positions, Nm, values of estimated Standard
from the following equation:
deviations, sm, and octave-band centre frequencies
Number of
SM = (n- 1)~ “’
[&CLpi + ‘] “’
microphone
Octave-band centre
positions, N,
%fl
frequency
3 6 12
where
Minimum
number of
is the Sound pressure level, in decibels,
Lpi
Source
at the ith measurement Position (refer-
dB Hz locations, Ns
ence: 20 ppa);
s, < 2,3 125 to 8 000 and A-weighting 1 1 1
is the mean value of Lp,, Lp2, . . . . LPG, in
125 1 1 1
Lp
2,3< s,< 4 250, 500 and A-weighting 2 2 1
decibels (reference: 20 ppa);
2 1 1
1 000 to 8 000
n is the number of microphone positions
125 3 2
(n = 6). SM > 4 250 and A-weighting 4 3 2
500 4 2 2
1 000 to 8 000 3 2 1
If the range of values of Lp.,, Lp2, . . . . LPG is not
greater than 5 dB, a simple arithmetic average
NOTE - For each Source Position, the mean-Square pressure
should be determined.
may be used for LJ. If the range is greater than
5 dB, q shall be calculated using the following
equ
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