EN ISO 3740:2000

SLOVENSKI STANDARD
01-september-2001
$NXVWLND8JRWDYOMDQMHUDYQL]YRþQLKPRþLYLURYKUXSD6PHUQLFH]DXSRUDER
WHPHOMQLKVWDQGDUGRY,62
Acoustics - Determination of sound power levels of noise sources - Guidelines for the
use of basic standards (ISO 3740:2000)
Akustik - Bestimmung der Schallleistungspegel von Geräuschquellen - Leitlinien zur
Anwendung der Grundnormen (ISO 3740:2000)
Acoustique - Détermination des niveaux de puissance acoustique émis par les sources
de bruit - Guide pour l'utilisation des normes de base (ISO 3740:2000)
Ta slovenski standard je istoveten z: EN ISO 3740:2000
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.

INTERNATIONAL ISO
STANDARD 3740
Second edition
2000-11-01
Acoustics — Determination of sound power
levels of noise sources — Guidelines for
the use of basic standards
Acoustique — Détermination des niveaux de puissance acoustique émis
par les sources de bruit — Guide pour l'utilisation des normes de base
Reference number
ISO 3740:2000(E)
©
ISO 2000
ISO 3740:2000(E)
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ii © ISO 2000 – All rights reserved

ISO 3740:2000(E)
Contents Page
Foreword.iv
Introduction.v
1 Scope .1
2 Normative references .1
3 Terms and definitions .2
4 Determination and declaration of sound power levels.5
4.1 Reasons for the determination of sound power levels.5
4.2 Methodology.5
5 Noise declaration according to ISO 4871.6
6 Selection of the appropriate International Standard for determination of sound power levels.6
6.1 Quantities to be measured and determined.6
6.2 Considerations affecting choice of method.6
6.3 Synopses.6
6.4 Test environments.6
6.5 Measurement uncertainty .7
6.6 Procedure for selection.7
Annex A (normative) Synopses of basic International Standards on sound power level determinations.11
Annex B (informative) Acoustical test environments.19
Annex C (informative) Factors affecting the choice of measurement method .21
Annex D (informative) Guidance on the choice of appropriate International Standard for determining
the sound power level of a sound source.23
Bibliography.25
ISO 3740:2000(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. Each member body interested in a subject for which a technical committee has been established has
the right to be represented 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 (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
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.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 3740 was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee
SC 1, Noise.
This second edition cancels and replaces the first edition (ISO 3740:1980), which has been technically revised.
Annex A forms a normative part of this International Standard. Annexes B to D are for information only.
iv © ISO 2000 – All rights reserved

ISO 3740:2000(E)
Introduction
0.1 General
The series of International Standards, for which this International Standard serves as a guideline for use, comprises
ISO 3741, ISO 3743-1, ISO 3743-2, ISO 3744, ISO 3745, ISO 3746, ISO 3747, ISO 9614-1 and ISO 9614-2. In
principle, the methods of determining sound power levels described in ISO 3741 to ISO 3747 and ISO 9614-1 and
ISO 9614-2 cover all types of machinery and equipment.
ISO 3741 to ISO 3747, ISO 9614-1 and ISO 9614-2 make up a set of basic International Standards which specify
the acoustical conditions and instrumentation to be used, describe the procedures to be followed, and give general
information on the mounting and operation of the machine under test in order to determine sound power levels.
The selection of standards for the determination of sound power levels can, for practical reasons, have
consequences for the selection of standards for the determination of the emission sound pressure levels (see
ISO 11200) and vice versa. It is beneficial to make the choice of standards concurrently with respect to the two
noise emission quantities.
0.2 Relationships to other standards
This International Standard is one of a series which specifies various methods for determining the noise emission
of a piece of machinery or equipment, or a sub-assembly of such equipment (referred to throughout this
International Standard as the "machine under test"). Standards in this series are grouped in three categories.
a) Methods for the determination of sound power levels
This category includes the following standards (see Table 1):
� ISO 3741 to ISO 3747 give methods with precision grade, engineering grade or survey grade of accuracy for
determining sound power levels of machinery and equipment using sound pressure level measurements in
different types of environments;
� ISO 9614-1 and ISO 9614-2 describe methods for determining the sound power levels of machinery and
equipment using sound intensity level measurements.
b) Methods for the determination of emission sound pressure levels at work stations and at other
specified positions
This category includes the following standards:
� ISO 11200 gives guidelines for the choice of the method to be used;
� ISO 11201, ISO 11202 and ISO 11204 give methods for determining emission sound pressure levels of
machinery and equipment from measured sound pressure levels;
� ISO 11203 gives methods for determining the emission sound pressure levels of machinery and equipment
from the sound power levels.
ISO 3740:2000(E)
c) Noise test codes
For a particular family of machinery or equipment, a noise test code specifies the following:
� the methods and instruments to be used for the determination of the sound power level;
� the method to be used for the determination of emission sound pressure levels at work stations and/or at other
specified positions;
� the positions of the work stations;
� the mounting and operating conditions of the machine under test for the purpose of determining the noise
emission quantities;
� the method to be used for verifying declared noise emission quantities.
ISO 12001 gives rules for the drafting and presentation of a noise test code.
vi © ISO 2000 – All rights reserved

INTERNATIONAL STANDARD ISO 3740:2000(E)
Acoustics — Determination of sound power levels of noise
sources — Guidelines for the use of basic standards
1 Scope
This International Standard gives guidance for the use of a series of nine International Standards describing
various methods for determining the sound power levels from all types of machinery and equipment. It provides:
� brief summaries of these basic International Standards;
� guidance on the selection of one or more of these standards which are appropriate to any particular type (see
clause 5 and annex D). The guidance given applies only to airborne sound. It is for use in the preparation of
noise test codes (see ISO 12001) and also in noise testing where no specific noise test code exists.
This International Standard is not intended to replace any of the details of, or add any additional requirements to,
the individual test methods in the other basic standards referred to.
These basic standards specify the acoustical requirements for measurements appropriate for different test
environments and accuracies.
It is important that specific test codes for various types of machinery and equipment be established and used in
accordance with the requirements of these basic International Standards. Such standardized noise test codes will
recommend the basic International Standard(s) to be used and will give detailed requirements on mounting and
operating conditions for a particular family to which the machine under test belongs.
If no specific noise test code exists for a particular type of machinery, this International Standard is of use for the
choice of the most suitable of the basic standards. In all cases, the mounting and operating conditions of the
machine under test should be in accordance with the general principles given in the basic standards.
NOTE Two quantities which complement each other can be used to describe the sound emission of machinery or
equipment. One is the emission sound pressure level at a specified position and the other is the sound power level. The
International Standards which describe the basic methods for determining emission sound pressure levels at the work station
and at other specified positions are the series ISO 11200 to ISO 11204.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 3741:1999, Acoustics — Determination of sound power levels of noise sources using sound pressure —
Precision methods for reverberation rooms.
ISO 3743-1, Acoustics — Determination of sound power levels of noise sources using sound pressure —
Engineering methods for small, movable sources in reverberant fields — Part 1: Comparison method for hard-
walled test rooms.
ISO 3740:2000(E)
ISO 3743-2:1994, 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 3744:1994, Acoustics — Determination of sound power levels of noise sources using sound pressure —
Engineering method in an essentially free field over a reflecting plane.
1)
ISO 3745:— , Acoustics — Determination of sound power levels of noise sources using sound pressure —
Precision methods for anechoic and hemi-anechoic rooms.
ISO 3746:1995, Acoustics — Determination of sound power levels of noise sources using sound pressure —
Survey method using an enveloping measurement surface over a reflecting plane.
ISO 3747, Acoustics — Determination of sound power levels of noise sources using sound pressure —
Comparison method in situ.
ISO 9614-1:1993, Acoustics — Determination of sound power levels of noise sources using sound intensity —
Part 1: Measurement at discrete points.
ISO 9614-2:1996, Acoustics — Determination of sound power levels of noise sources using sound intensity —
Part 2: Measurement by scanning.
ISO 12001, Acoustics — Noise emitted by machinery and equipment — Rules for the drafting and presentation of a
noise test code.
IEC 61672-1, Electroacoustics — Sound level meters — Part 1: Specifications.
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply. More detailed definitions
may be found in the ISO 3740 series (which includes ISO 3741 through ISO 3747), in ISO 9614-1 and ISO 9614-2
and in noise test codes for specific types of machinery and equipment.
3.1
emission
airborne sound radiated by a well-defined noise source (e.g. the machine under test) under specified operating and
mounting conditions
NOTE Emission values may be incorporated in a product label and/or product specification. The basic noise emission
quantities are the sound power level of the source itself and the emission sound pressure levels at the work station and/or at
other specified positions (if any) in the vicinity of the source.
[ISO 12001]
3.2
sound power
W
rate per unit time at which airborne sound energy is radiated by a source
NOTE It is expressed in watts.
[ISO 12001]
1) To be published. (Revision of ISO 3745:1977)
2 © ISO 2000 – All rights reserved

ISO 3740:2000(E)
3.3
sound power level
L
W
ten times the logarithm to the base 10 of the ratio of the sound power radiated by the source under test to the
�12
reference sound power [W =1pW (10 W)]
NOTE 1 It is expressed in decibels.
NOTE 2 The frequency weighting or the width of the frequency band used should be indicated; for example A-weighted
sound power level (L ).
WA
NOTE 3 Adapted from ISO 12001.
3.4
sound pressure level
L
p
ten times the logarithm to the base 10 of the ratio of the square of the sound pressure to the square of the
�5
reference sound pressure [p =20�Pa (2� 10 Pa)]
NOTE 1 It is expressed in decibels.
NOTE 2 The frequency weighting or the width of the frequency band used, and the time weighting (S, F or I, see
IEC 61672-1) should be indicated.
NOTE 3 Adapted from ISO 3744.
3.5
time-averaged sound pressure level
L
peqT
sound pressure level of a continuous steady sound that, within a measurement time interval T, has the same mean-
square sound pressure as a sound under consideration which varies with time:
T
��
1(pt)
��
Lt� 10 lg ddB (1)
pTeq
�
��T
p
��0
NOTE 1 It is expressed in decibels.
NOTE 2 A-weighted time-averaged sound pressure levels are denoted by L , which is usually abbreviated to L . L
pAeqT pA pAeqT
shall be measured with an instrument which complies with the requirements of IEC 61672-1.
NOTE 3 In general, the subscripts "eq" and "T" are omitted since time-averaged sound pressure levels are necessarily
determined over a certain measurement time interval.
NOTE 4 Adapted from ISO 12001.
3.6
sound energy level
L
J
ten times the logarithm to the base 10 of the ratio of the sound energy E (in joules) of the single burst of sound or
�12
transient sound radiated by the sound source under test to the reference sound energy [E =1pJ (10 J)]:
LE� 10lg(/E )dB (2)
J0
NOTE 1 It is expressed in decibels.
NOTE 2 The frequency weighting or the width of the frequency band used should be indicated.
ISO 3740:2000(E)
3.7
single-event sound pressure level
L
p,1s
time-integrated sound pressure level of an isolated single sound event of specified duration T (or specified
measurement time T) normalized to T =1s:
T
��2
1(pt)
��
Lt� 10 lg ddB
p,1s
�
��T
0 p
��
��T
��L 10 lg dB (3)
pTeq ��
T
��
NOTE 1 It is expressed in decibels.
NOTE 2 Adapted from ISO 3744.
3.8
sound intensity
�
I
product of the sound pressure at a point and the associated particle velocity
NOTE It is a vectorial quantity.
3.9
background noise
noise from all sources other than the source under test
NOTE Background noise may include contributions from airborne sound, structure-borne vibration, and electrical noise in
instrumentation.
[ISO 3744]
3.10
background noise level
sound pressure level measured when the source under test is not operating
NOTE It is expressed in decibels.
3.11
background noise correction
K
correction term to account for the influence of background noise on the surface sound pressure level
NOTE 1 K is frequency dependent and is expressed in decibels.
NOTE 2 The correction in the case of A-weighting is denoted K
1A.
[ISO 3744]
3.12
environmental correction
K
correction term to account for the influence of reflected or absorbed sound on the surface sound pressure level
NOTE 1 K is frequency dependent and is expressed in decibels.
4 © ISO 2000 – All rights reserved

ISO 3740:2000(E)
NOTE 2 The correction in the case of A-weighting is denoted K .
2A
[ISO 3744]
NOTE 3 K is used in standards of the ISO 3740 series employing an enveloping measurement surface.
4 Determination of sound power levels
4.1 Reasons for the determination of sound power levels
The effective exchange of acoustical information among the several parties concerned is usually needed to control
the noise from machinery and equipment. These include the manufacturer, installer, and user of the machinery or
equipment. This acoustical information is obtained from measurements. These measurements are useful only if the
conditions under which they are carried out are specified, if they yield defined acoustical quantities, and if they are
made using standardized instruments.
Sound power levels may be used for different purposes:
� declaration of the noise emitted under defined conditions (see clause 5);
� verification of declared values;
� comparison of the noise emitted by machinery of various types and sizes;
� comparison with limits specified in a purchasing contract or a regulation;
� engineering work to reduce the noise emission of machinery;
� prediction of noise levels in work places;
� establishment of a list of requirements from the client to the supplier and/or elaboration of a contract with
reference to a standardized method;
� characterization and description of the source.
The sound power level data determined according to one of the basic International Standards are essentially
independent of the environment in which the data are obtained or in which the machinery or equipment is to be
installed. This is one of the reasons for using sound power levels to characterize the noise emitted by various types
of machinery and equipment.
4.2 Methodology
The two main principles for the determination of the sound power level of a machine or equipment applied in the
ISO 3740 and ISO 9614 series are:
� evaluation of the spatial mean-squared sound pressure built up in a highly reflective environment
(measurements in a reverberant field);
� evaluation of the flow of sound energy emitted by the source, with measurements using an enveloping surface
(measurements in a free field or in a free field over a reflecting plane or in a more or less free field over a
reflecting plane).
Two basic quantities can be measured to determine the sound power level of a machine or equipment, i.e. sound
pressure levels or sound intensity levels. Seven International Standards in the ISO 3740 series describe
procedures for determining sound power levels from measured sound pressure levels, in different test
environments. ISO 9614-1 and ISO 9614-2 give procedures for determining sound power levels from measured
values of the sound intensity components in the vicinity of the machine under test.
ISO 3740:2000(E)
5 Noise declaration according to ISO 4871
The sound power level determined according to one of the methods described in this International Standard and
the related uncertainty are two quantities that are used by manufacturers of machinery and equipment when
preparing the noise declaration according to ISO 4871. Values of the uncertainty are normally given in the relevant
noise test code. If no specific noise test code exists, values given in annex A of ISO 4871:1996 can be used.
6 Selection of the appropriate International Standard for determination of sound power
levels
6.1 Quantities to be measured and determined
Methods are specified in ISO 3741 to ISO 3747 for determining sound power levels by measuring sound pressure
levels. Methods are specified in ISO 9614-1 and ISO 9614-2 for determining sound power levels by measuring
sound intensity levels.
The levels may be time-averaged, frequency-weighted, in frequency bands, or time-weighted. The preferred
frequency weighting is A-weighting.
6.2 Considerations affecting choice of method
Factors to be considered when selecting a standard from this series of International Standards include the
following:
a) the grade of accuracy required (see ISO 12001 for the definition);
b) the size and transportability of the machinery or equipment, affecting the practicability of setting it up in an
acoustical test laboratory for the purpose of the noise measurements;
c) the test environment available for the measurements;
d) the background noise level;
e) the character of the noise produced by the source (e.g. broad-band, narrow-band, discrete-frequency; steady,
non-steady, impulsive);
f) the acoustical instrumentation available;
g) the type of sound power level required (frequency-weighted or in frequency bands, frequency range of
interest);
h) other acoustical information desired (e.g. directivity of source, temporal pattern).
NOTE 1 The preferred grade of accuracy for purposes of noise declaration is engineering (grade 2).
NOTE 2 All standards within a specific grade imply the same level of accuracy.
6.3 Synopses
Synopses of ISO 3741 to ISO 3747 and ISO 9614-1 and ISO 9614-2 are given in annex A. Table 1 gives an
overview of these International Standards.
6.4 Test environments
Annex B describes the different test environments considered in ISO 3741 to ISO 3747, and ISO 9614-1 and
ISO 9614-2.
6 © ISO 2000 – All rights reserved

ISO 3740:2000(E)
6.5 Measurement uncertainty
The standard deviations given in Table 2 represent the worst cases of measurement uncertainty for the
determination of sound power levels in accordance with these test methods. They reflect the cumulative effects of
all causes of measurement uncertainty, excluding those variations in the sound power level from test to test, which
may be caused, for example, by changes in the mounting or operating conditions of the machine under test.
Furthermore, the standard deviations given in Table 2 cover a great variety of sound source parameters such as
very different spectral contents and directional properties. For a well-defined specific machinery family, the range of
variation of parameter values may be considerably smaller. Therefore, for measurements on a specific machinery
family, standard deviations are smaller.
When preparing a noise test code, an interlaboratory test for the relevant family of machinery is recommended in
order to determine the relevant standard deviations (see ISO 5725-2 for details).
6.6 Procedure for selection
Table 1 summarizes the applicability of each of the nine basic International Standards. Table 2 gives the
uncertainties involved in the determination of the sound power levels according to these standards.
The purpose(s) for which the noise measurements are to be made determine(s) the grade of accuracy required.
The different factors influencing the selection of an appropriate test method are shown in Table 3. Additional
information is given in annex C. Table 3 and annex D give guidance for the selection of the appropriate
International Standard.
ISO 3740:2000(E)
8 © ISO 2000 – All rights reserved
Table 1 — Overview of International Standards for determination of sound power levels of machines and equipment
Using sound pressure Using sound intensity
ISO 9614-1
Parameter
ISO 3741 ISO 3743-1 ISO 3743-2 ISO 3744 ISO 3745 ISO 3746 ISO 3747 ISO 9614-2
Precision, engineering or
a a a a a a a a
Precision Engineering Engineering Engineering Precision Survey Engineering or survey Engineering or survey
a
survey
Essentially reverberant field
Essentially free-field
Special reverberation Anechoic or hemi- No special test
in situ, subject to stated
Test environment Reverberation room Hard-walled room over a reflecting Any Any
room anechoic room environment
qualification requirements
plane
Specified requirements for: Specified requirements for:
3 3 — extraneous intensity — extraneous intensity
VolumeW 40 m 70 m u volume
Room volume and
Criterion for suitability of 3 Specified — wind, gas flow, vibration, — wind, gas flow, vibration,
b b
u 300 m
reverberation time to K u2dB K u7dB Specified requirements
Absorption coef. 2 2
test environment requirements temperature temperature
be qualified
u 0,20 0,5 su T u1s
nom — configuration of — configuration of
surrounding surrounding
No restrictions; Characteristic No restrictions;
Preferably less than Preferably less than Preferably less than No restrictions;
limited only by dimension less than limited only by
2 % of test room 1 % of test room 1 % of test room limitedonlybyavailable
Volume of sound source No restrictions No restrictions
available test half measurement available test
volume volume volume test environment
environment radius environment
Steady, broad-band, Steady, broad-band, Broadband, narrow-band or Broadband, narrow-band or
Character of noise Any, but no isolated Any, but no isolated
narrow-band or Any Any Any narrow-band or discrete discrete frequency, if stationary discrete frequency, if
from the source bursts bursts
discrete frequency frequency in time stationary in time
Level: given by dynamic
Level: given by dynamic
capability of the
capability of the instrumentation
instrumentation (typically:
�LW 10 dB �LW 6dB �LW 4dB �LW 6dB �LW 10 dB �LW 3dB �LW 6dB
Limitation for background (typically:
�LW�10 dB
noise c c c c c c c �LW�10 dB
K u 0,5 dB K u 1,3 dB K u2dB K u 1,3 dB K u 0,5 dB K u3dB K u 1,3 dB
1 1 1 1 1 1 1 Variability: specified
Variability: specified requirement
requirement for repeatability
for field indicator F1
check
d
Instrumentation:
a) sound level meter a) class 1 a) class 1 a) class 1 a) class 1 a) class 1 a) class 1 a) class 1
b) integrating sound b) class 1 b) class 1 b) class 1 b) class 1 b) class 1 b) class 1 b) class 1
level meter
c) frequency band filter c) class 1 c) class 1 c) class 1 c) class 1 c) class 1 c) class 1 c) class 1
d) calibrator d) class 1 d) class 1 d) class 1 d) class 1 d) class 1 d) class 1 d) class 1
e e
e) sound intensity e) class 1 or 2 e) class 1 or 2
instrument
Band limited (one-third-octave
Band limited (one-third-octave
50 Hz-6 300 Hz) A-weighted
50 Hz-6 300 Hz) A-weighted and
A-weighted and in A-weighted and in A-weighted and in and in one-third-octave or
Sound power levels A-weighted and in A-weighted and in A-weighted from octave in one-third-octave or octave
one-third-octave or one-third-octave or one-third-octave or A-weighted octave bands.
bands.
obtainable octave bands octave bands bands
octave bands octave bands octave bands Grade of accuracy is
Grade of accuracy is determined
determined from field
from field indicators
indicators
Directivity information and sound pressure
Other frequency- Other frequency- Other frequency- Sound pressure
Optional information levels as a function of time; single-event Sound pressure levels as a Positive and/or negative partial
weighted sound weighted sound weighted sound levels as
available sound pressure levels; other frequency- function of time sound power concentration
power levels power levels power levels function of time
weighted sound power levels
— Sound energy levels
a
Grade of accuracy: precision = grade 1; engineering = grade 2; survey = grade 3.
b
K is the environmental correction (see 3.12)
c
K is the correction for background noise (see 3.11)
d
At least complying with class " " of:
a) IEC 61672-1, b) IEC 61672-1, c) IEC 61260, d) IEC 60942, e) IEC 61043.
e
According to the grade of accuracy of the method (class 1 for precision and engineering and class 2 for survey).

ISO 3740:2000(E)
Table 2 — Uncertainty in determining sound power levels, expressed as the largest value of the standard deviation of reproducibility
Values in decibels
ISO ISO ISO ISO ISO 3745 ISO 3745 ISO 3746 ISO 3747 ISO ISO ISO ISO ISO
3741 3743-1 3743-2 3744 9614-1 9614-1 9614-1 9614-2 9614-2
Frequency
Anechoic Hemi- Engineering Survey Precision Engineer- Survey Engineer- Survey
room anechoic ing ing
room
a
(if K u 5dB)
a
(if 5� K u7dB)
a b b b
A-weighting 0,5 1,5 2 1,5 —— 1,5 4 —— 4 1,5 4
c
(if K u 5dB)
c
(if 5� K u7dB)
Octave bands (Hz)
d
63 —— — 5 —— — — 23 — 3 —
125 2,5 3 5 3 —— — — 23 — 3 —
250 1,5 2 3 2 —— — — 1,5 2 — 2 —
500 1,0 1,5 2 1,5 —— — — 1,5 2 — 1,5 —
1 000 to 4 000 1,0 1,5 2 1,5 —— — — 11,5 — 1,5 —
8 000 2 2,5 3 2,5 — — — — ——— — —
One-third-octave
bands (Hz)
d
50 to 80 —— — 5 22 —— 23 — 3 —
100 to 160 3,0 —— 31 1,5 —— 23 — 3 —
200 to 315 2,0 —— 21 1,5 —— 1,5 2 — 2 —
400 to 630 1,5 —— 1,5 1 1,5 —— 1,5 2 — 1,5 —
800 to 5 000 1,5 —— 1,5 0,5 1 —— 11,5 — 1,5 —
e e e
6 300 to 10 000 3 —— 2,5 1 1,5 —— 2 2,5 — 2,5 —
a
For a source which emits noise with a relatively "flat" spectrum over the frequency range of interest.
b
A-weighted (from octave bands, 63 Hz to 4 000 Hz, or from one-third-octave bands, 50 Hz to 6 300 Hz).
c
For a source which emits noise that contains predominant discrete tones.
d
Normally for outdoor measurements; many rooms are not qualified for this frequency band.
e
One-third-octave band 6 300 Hz only.
— Notstatedinthestandard.
ISO 3740:2000(E)
10 © ISO 2000 – All rights reserved
Table 3 — Factors influencing the choice of the method
ISO ISO ISO ISO ISO ISO ISO ISO ISO
3741 3743-1 3743-2 3744 3745 3746 3747 9614-1 9614-2
Precision (grade 1) x x x
Grade of accuracy Engineering (grade 2) xxx x x x
Survey (grade 3) x x x x
Reverberation room x
Environment specifically
Special reverberation test room x
designed for the
Anechoic room x
determination of sound
a
Hemi-anechoic room x x
power
Hard-walled test room x
Indoors in a sufficiently reverberant field xx x
Indoors in an approximate free field over a b x x
x
In-situ environment reflecting plane
Outdoors and indoors in an essentially free x x
x
field over a reflecting plane
�LW 10 dB xx x x xx x x x
�LW 6dB x x x x x x x
Background noise level
�LW 3dB x x x
c c
�L<3dB x x
All types as defined in ISO 12001 xx x
Character of noise All types, except isolated bursts xx x x
Stationary in time xx
Sound level meter:
class 1 x x x x x x
class 2 x
Instrumentation Integrating sound level meter:
(see Table 1) class 1 x x x x x x
class 2 x
Frequency band filter class 1 x x x x x x
Sound intensity instrument xx
One-third-octave band levels x x x x x
Sound power levels
Octave-band levels x x x x x x x x
obtainable
d d
A-weighted levels x x x x xx x x x
Other frequency weightings x xxx x x x
Optional information
Directivity information x x
available
Temporal pattern x x x
a c
Environmental correction K u 2dB Lower limit is approximately –10 dB, but it depends on measurement conditions.
b d
Environmental correction K u7dB A-weighted (from octave bands, 63 Hz to 4 000 Hz, or from one-third-octave bands, 50 Hz to 6 300 Hz).
x Applicable
ISO 3740:2000(E)
Annex A
(normative)
Synopses of basic International Standards on sound power level
determinations
A.1 ISO 3741 — Precision method for reverberation rooms
A.1.1 Applicability
The test environment shall be a reverberation room with a specified shape and a volume less than 300 m and
greater than or equal to:
� 70 m for a lowest octave band of interest of 250 Hz (or 200 Hz one-third-octave band);
� 100 m for a lowest one-third-octave band of interest of 160 Hz;
� 150 m for a lowest one-third-octave band of interest of 125 Hz;
� 200 m for a lowest octave band of interest of 125 Hz (or 100 Hz one-third octave band).
For rooms that do not meet the volume requirements, annex E provides a procedure for qualifying the room for the
measurement of broad-band sound.
Guidelines for the design of reverberation rooms are given in annexes B and C of ISO 3741:1999.
The type of noise source includes machines, devices, components and sub-assemblies.
The noise source shall have a volume preferably less than 2 % of the volume of the test room.
The character of the noise radiated by the source includes all types of noise as defined in ISO 12001, except
impulsive noise. More microphone and source positions may be necessary when noise emission contains discrete-
frequency components. Annex A of ISO 3741:1999 provides a procedure for qualifying the room for the
measurement of discrete-frequency components.
A.1.2 Measurement uncertainty
The standard deviation of reproducibility is equal to or less than 0,5 dB for A-weighted sound power levels (for
sources which emit noise with a relatively "flat" spectrum). In one-third-octave bands, it is equal to or less than 3 dB
from 100 Hz to 160 Hz, 2 dB from 200 Hz to 315 Hz, 1,5 dB from 400 Hz to 5 000 Hz and 3 dB from 6 300 Hz to
10 000 Hz. In octave bands, it is equal to or less than 2,5 dB for 125 Hz, 1,5 dB for 250 Hz, 1 dB from 500 Hz to
4 000 Hz and 2 dB for 8 000 Hz.
A.1.3 Quantities to be measured
These are sound pressure levels in one-third-octave-frequency bands at specified fixed microphone positions or
along specified paths. Measurements can be made using either the direct method or the comparison method using
a reference sound source.
ISO 3740:2000(E)
A.1.4 Quantities to be determined
These include:
� sound power levels in frequency bands;
� A-weighted sound power levels calculated from the frequency band sound power levels;
� optionally, sound power levels with other frequency weightings.
A.1.5 Quantities which cannot be determined
These include:
� directivity characteristics of the source;
� time history of noise radiated by sources emitting non-steady noise.
A.2 ISO 3743 — Engineering methods for small, movable sources in reverberant fields
A.2.1 ISO 3743-1 — Comparison method for hard-walled test rooms
A.2.1.1 Applicability
The test environment shall be a test room with a volume greater than 40 m and greater than 40 times the volume
of the reference box and with surfaces that are hard and sound-reflective. It shall be ensured that, at all
frequencies, the sound absorption coefficient of any boundary surface does not exceed 0,20.
The type of noise source includes small machines, devices, components and sub-assemblies. ISO 3743-1 is
particularly suitable for small items of portable equipment and is not intended for larger pieces of stationary
equipment.
The size of the noise source shall be such that its largest dimension is not greater than 1,0 m in a test room with a
volume less than 100 m and not greater than 2,0 m in larger test rooms.
The character of the noise radiated by the source includes all types of noise as defined in ISO 12001, except
isolated bursts of noise.
A.2.1.2 Measurement uncertainty
The standard deviation of reproducibility is equal to or less than 1,5 dB (with few exceptions) for A-weighted sound
power levels. In octave frequency bands, it is equal to or less than 3 dB for 125 Hz, 2 dB for 250 Hz, 1,5 dB from
500 Hz to 4 000 Hz, and 2,5 dB for 8 000 Hz.
A.2.1.3 Quantities to be measured
These are sound pressure levels in octave bands at specified fixed microphone positions or along specified paths.
A.2.1.4 Quantities to be determined
These include:
� sound power levels in octave bands;
� A-weighted sound power levels calculated from the octave-band sound power levels.
12 © ISO 2000 – All rights reserved

ISO 3740:2000(E)
A.2.1.5 Quantities which cannot be determined
These include:
� directivity characteristics of the source;
� time history of noise radiated by sources emitting non-steady noise.
A.2.2 ISO 3743-2 — Methods for special reverberation test rooms
A.2.2.1 Applicability
The test environment shall be a special reverberation room with specified characteristics. The volume shall be
3 3
between 70 m and 300 m . The reverberation time of the room at low and middle frequencies shall be reduced to
the recommended values by installing sound-absorptive materials on the walls and ceiling. Guidelines for the
design of special reverberation test rooms are given in annex A of ISO 3743-2:1994.
The type of noise source includes small machines, devices, components and sub-assemblies. ISO 3743-2 is
particularly suitable for small items of portable equipment and is not intended for larger pieces of stationary
equipment.
The size of the noise source shall preferably be such that its volume is not greater than 1 % of the volume of the
test room.
The character of the noise radiated by the source includes all types of noise as defined in ISO 12001, except
isolated bursts of noise.
A.2.2.2 Measurement uncertainty
The standard deviation of reproducibility is equal to or less than 2 dB (with few exceptions) for A-weighted sound
power levels. In octave frequency bands, it is equal to or less than 5 dB for 125 Hz, 3 dB for 250 Hz, 2 dB from
500 Hz to 4 000 Hz, and 3 dB for 8 000 Hz.
A.2.2.3 Quantities to be measured
These include:
� A-weighted sound pressure levels for the direct method, at specified fixed microphone positions or along
specified paths;
� sound pressure levels in octave bands for the comparison method, at specified fixed microphone positions or
along specified paths.
A.2.2.4 Quantities to be determined
These include:
� for the direct method, A-weighted sound power levels;
� for the comparison method, sound power levels in octave bands and A-weighted sound power levels
calculated from the octave-band sound power levels.
ISO 3740:2000(E)
A.2.2.5 Quantities which cannot be determined
These include:
� directivity characteristics of the source;
� time history of noise radiated by sources emitting non-steady noise.
A.3 ISO 3744 — Engineering method employing an enveloping measurement surface in
an essentially free field over a reflecting plane
A.3.1 Applicability
The test environment shall be an essentially free field near one or more reflecting planes (indoors or outdoors).
The test environment may be a hemi-anechoic room, or a large ordinary test room, if qualified as follows. The
adequacy of the test environment shall be checked according to one of the test procedures given in annex A of
ISO 3744:1994. The reflecting plane(s) on which the source is located shall extend at least to the measurement
surface. The sound absorption coefficient of the reflecting plane(s) should preferably be less than 0,06. The
environmental correction K shall not exceed 2 dB (corresponding to a ratio A/SW 6 for rooms where A is the
equivalent sound absorption area of the test room and S is the area of the measurement surface).
The type of noise source include any stationary or moving source for indoor or outdoor use.
The size of the noise source is limited only by the available test environment.
The character of the noise radiated by the source includes all types of noise as defined in ISO 12001.
A.3.2 Measurement uncertainty
The standard deviation of reproducibility is equal to or less than 1,5 dB for A-weighted sound power levels (for
sources which emit noise with a relatively flat spectrum). In one-third octave bands it is equal to or less than 5 dB
from 50 Hz to 80 Hz, 3 dB from 100 Hz to 160 Hz, 2 dB from 200 Hz to 315 Hz, 1,5 dB from 400 Hz to 5 000 Hz
and 2,5 dB from 6 300 Hz to 10 000 Hz. In octave bands it is equal to or less than 5 dB for 63 Hz, 3 dB for 125 Hz,
2 dB for 250 Hz, 1,5 dB from 500 Hz to 4 000 Hz and 2,5 dB for 8 000 Hz.
A.3.3 Quantities to be measured
These are sound pressure levels, A-weighted and/or in frequency bands, at specified fixed microphone positions or
along s
...