SIST EN ISO 3740:2019

SLOVENSKI STANDARD
01-julij-2019
Nadomešča:
SIST EN ISO 3740:2001
Akustika - Ugotavljanje ravni zvočnih moči virov hrupa - Smernice za uporabo
temeljnih standardov (ISO 3740:2019)
Acoustics - Determination of sound power levels of noise sources - Guidelines for the
use of basic standards (ISO 3740:2019)
Akustik - Bestimmung der Schallleistungspegel von Geräuschquellen - Leitlinien zur
Anwendung der Grundnormen (ISO 3740:2019)
Acoustique - Détermination des niveaux de puissance acoustique émis par les sources
de bruit - Lignes directrices pour l'utilisation des normes de base (ISO 3740:2019)
Ta slovenski standard je istoveten z: EN ISO 3740:2019
ICS:
17.140.01 Akustična merjenja in Acoustic measurements and
blaženje hrupa na splošno noise abatement in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 3740
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2019
EUROPÄISCHE NORM
ICS 17.140.01 Supersedes EN ISO 3740:2000
English Version
Acoustics - Determination of sound power levels of noise
sources - Guidelines for the use of basic standards (ISO
3740:2019)
Acoustique - Détermination des niveaux de puissance Akustik - Bestimmung der Schallleistungspegel von
acoustique émis par les sources de bruit - Lignes Geräuschquellen - Leitlinien zur Anwendung der
directrices pour l'utilisation des normes de base (ISO Grundnormen (ISO 3740:2019)
3740:2019)
This European Standard was approved by CEN on 8 February 2019.

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-CENELEC 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-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 3740:2019 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 3740:2019) has been prepared by Technical Committee ISO/TC 43 "Acoustics"
in collaboration with Technical Committee CEN/TC 211 “Acoustics” the secretariat of which is held by
DIN.
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 September 2019, and conflicting national standards
shall be withdrawn at the latest by September 2019.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 3740:2000.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association.
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,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 3740:2019 has been approved by CEN as EN ISO 3740:2019 without any modification.

INTERNATIONAL ISO
STANDARD 3740
Third edition
2019-02
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 — Lignes directrices pour l'utilisation
des normes de base
Reference number
ISO 3740:2019(E)
©
ISO 2019
ISO 3740:2019(E)
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

ISO 3740:2019(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Sound power level . 7
4.1 Basic information . 7
4.2 Reasons for the determination of sound power levels . 7
4.3 Basic procedures for determining sound power levels . 7
4.4 Quality of determined sound power levels . 8
4.5 Noise emission declaration . 8
5 Selection of the most appropriate method in the set of standards . 9
5.1 Methods and quantities to be measured and determined. 9
5.2 Considerations affecting the selection of a measurement method . 9
5.3 Test environment .17
5.4 Selection of basic standards appropriate for measurements in laboratory rooms
and special test rooms .17
5.4.1 General.17
5.4.2 Acoustical requirements on the sound field in laboratories and special
test rooms .17
5.4.3 Background noise limitation .17
5.5 Selection of basic standards appropriate for in-situ measurements .18
5.5.1 General.18
5.5.2 Hemi-anechoic sound field check .19
5.6 Determination of high-frequency sound power levels .20
Annex A (informative) Basic International Standards specifying methods for determining
sound power levels of machines, equipment and products — Main facts and
requirements.21
Annex B (informative) Acoustical test environments .23
Annex C (informative) Measurement uncertainty .25
Annex D (informative) Case studies .28
Bibliography .34
ISO 3740:2019(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.
This third edition cancels and replaces the second edition (ISO 3740:2000), which has been technically
revised. The main change compared to the previous edition is as follows:
— All of the basic standards covered by this document with the exception of the ISO 9614 series
have been revised.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2019 – All rights reserved

ISO 3740:2019(E)
Introduction
For many users of machinery, equipment and products, the control of noise is a major issue which
requires effective exchange of acoustical information. In this context, the main flow of information goes
from the manufacturer to the purchaser, installer or user of the machines and products to describe the
generated sound. In particular, information on source airborne noise emission is desired. Therefore,
the sound power level, as the major parameter characterising airborne noise emission of sound sources,
needs to be determined by measurement.
However, such measurements are only useful if the conditions under which they are carried out are
specified; they yield defined acoustical quantities, and they are taken with standardized instruments.
Sound power levels are used for
— declaration of the noise emitted under defined conditions,
— 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 control the noise emission of machinery,
— prediction of noise exposure of workers in indoor or outdoor work shops,
— prediction of noise in the environment.
International Standards describing basic methods for determining sound power level are
— ISO 3741 to ISO 3747 (sound power level determination using sound pressure level measurements),
— ISO 9614-1 to ISO 9614-3 (sound power level determination using sound intensity measurements),
— ISO/TS 7849-1 and ISO/TS 7849-2 (sound power level determination using vibration measurements).
These standards specify different methods for determination of sound power level and the achievable
accuracy, characterized by the standard deviation of reproducibility of the method. Operating and
mounting conditions, and the uncertainty associated with these conditions, are dealt with only in a
very general manner. Specific and detailed requirements on the machinery or equipment under test
are given in noise test codes prepared by machinery specific standards committees. They not only
provide the necessary detailed information on the operating, installation and mounting conditions but
also identify basic measurement standards that can be used and how a noise emission declaration and
verification is made.
The standards mentioned above differ in their range of applications and their requirements with regard
to the test environment. In practice, procedures that do not require special laboratory environments and
additionally meet class 2 accuracy are particularly advantageous, especially to meet legal requirements.
These include the procedures in standards ISO 3744, ISO 3747 and methods in ISO 9614-2.
To help technical committees in drafting noise test codes or to assist manufacturers of machines and
equipment in determining the sound power level if a noise test code is not currently available, ISO 3740
introduces the set of twelve International Standards describing various methods for determining sound
power levels of machinery, equipment and products taking into account the broad variety of practical
situations for the sources under test (types of machinery, equipment and products), test environments,
measurement instruments and the accuracy desired.
Some machinery, equipment and products emit high-frequency noise, which can be broad-band noise,
narrow-band noise or discrete tones. ISO 9295 specifies four methods for the determination of sound
power levels emitted by machinery, equipment and products in the frequency range covered by the
16 kHz octave band. In 5.6, ISO 9295 is briefly described.
ISO 3740:2019(E)
More detailed definitions than those specified in this document can be found in ISO 3741, ISO 3743-1,
ISO 3743-2, ISO 3744, ISO 3745, ISO 3746 and ISO 3747, in ISO 9614-1 to ISO 9614-3, ISO/TS 7849-1, ISO/
TS 7849-2, and in noise test codes for specific types of machinery, equipment and products.
vi © ISO 2019 – All rights reserved

INTERNATIONAL STANDARD ISO 3740:2019(E)
Acoustics — Determination of sound power levels of noise
sources — Guidelines for the use of basic standards
1 Scope
This document gives guidance for the use of a set of twelve basic International Standards (see Tables 1,
2 and 3) describing various methods for determining sound power levels from all types of machinery,
equipment and products. It provides guidance on the selection of one or more of these standards,
appropriate to any particular type of sound source, measurement environment and desired accuracy.
The guidance given applies to airborne sound. It is for use in the preparation of noise test codes (see
ISO 12001) and also in noise emission testing where no specific noise test code exists. Such standardized
noise test codes can recommend the application of particular basic International Standard(s) and give
detailed requirements on mounting and operating conditions for a particular family to which the
machine under test belongs, in accordance with general principles given in the basic standards.
This document is not intended to replace any of the details of, or add any additional requirements to,
the individual test methods in the basic International Standards referenced.
NOTE 1 Two quantities which complement each other can be used to describe the noise emission of machinery,
equipment and products. 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 work stations and at other specified positions are ISO 11200 to ISO 11205 (References
[20] to [25]).
NOTE 2 The sound energy level mentioned in ISO 3741 to ISO 3747 is not addressed in this document as it is
not mentioned in any legal requirement. Its application is limited to very special cases of a single burst of sound
energy or transient sound defined in ISO 12001.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
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 1 to entry: Emission values may be incorporated into a product noise declaration, 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.
[SOURCE: ISO 12001:1996, 3.3, modified — Note 1 to entry "product noise declaration" added.]
ISO 3740:2019(E)
3.2
sound power
P
through a surface, product of the sound pressure, p, and the component of the particle velocity, u , at a
n
point on the surface in the direction normal to the surface, integrated over that surface
Note 1 to entry: Sound power is expressed in watts.
Note 2 to entry: The quantity relates to the rate at which airborne sound energy is radiated by a source.
[SOURCE: ISO 80000-8:2007, 8-16, modified — Notes 1 and 2 to entry added.]
3.3
sound power level
L
W
ten times the logarithm to the base 10 of the ratio of the sound power, P (3.2), of a source to a reference
value, P , expressed in decibels
P
L =10lg dB
W
P
where the reference value, P , is 1 pW
Note 1 to entry: If a specific frequency weighting as specified in IEC 61672-1 and/or specific frequency bands are
applied, this is indicated by appropriate subscripts; e.g. L denotes the A-weighted sound power level.
WA
Note 2 to entry: This definition is technically in accordance with ISO 80000-8:2007, 8-23.
Note 3 to entry: lg ( ) = lg ( ) in all relevant parts of the standard.
[SOURCE: ISO/TR 25417:2007, 2.9, modified — Note 3 to entry added.]
3.4
structure vibration generated sound
airborne sound caused by structural vibration in the audible frequency range
Note 1 to entry: In the ISO/TS 7849 series, structure vibration generated sound is determined either from the
vibratory velocity or from the vibratory acceleration of the surface of the solid structure.
[SOURCE: ISO/TS 7849-1:2009, 3.1, modified — Expression "In the ISO/TS 7849 series" used for
clarification instead of "For the purpose of this part of ISO/TS 7849".]
3.5
sound pressure level
L
p
ten times the logarithm to the base 10 of the ratio of the square of the sound pressure, p, to the square
of a reference value, p , expressed in decibels
p
L =10lg dB
p
p
where the reference value, p , is 20 μPa
[SOURCE: ISO/TR 25417:2007, 2.2, modified — Notes 1 and 2 deleted.]
2 © ISO 2019 – All rights reserved

ISO 3740:2019(E)
3.6
time-averaged sound pressure level
L
p,T
ten times the logarithm to the base 10 of the ratio of the time average of the square of the sound
pressure, p, during a stated time interval of duration, T (starting at t and ending at t ), to the square of
1 2
a reference value, p , expressed in decibels
t
 2 
pt dt
()
 
∫
t
T
L =10lg dB
pT,
 
p
 
 
where the reference value, p , is 20 μPa
Note 1 to entry: In general, the subscript “T” is omitted since time-averaged sound pressure levels are necessarily
determined over a certain measurement time interval.
Note 2 to entry: Time-averaged sound pressure levels are often A-weighted, in which case they are denoted by
L , which is usually abbreviated to L .
pA,T pA
Note 3 to entry: Adapted from ISO/TR 25417:2007, 2.3.
[SOURCE: ISO 3744:2010, 3.3]
3.7
single event time-integrated sound pressure level
L
E
ten times the logarithm to the base 10 of the ratio of the integral of the square of the sound pressure,
p, of an isolated single sound event (burst of sound or transient sound) over a stated time interval T
(starting at t and ending at t ), to a reference value, E , expressed in decibels
1 2 0
t
 
pt dt
()
 
∫
t
 
L =10lg dB
E
E
 
 
 
2 −10 2
where the reference value, E , is (20 μPa) s = 4 × 10 Pa s
Note 1 to entry: This quantity can be obtained by

 T
L +10lg dB
pT,  
T
 0 
where T = 1 s.
Note 2 to entry: When used to measure sound immission, this quantity is usually called “sound exposure level”
(see ISO/TR 25417:2007).
[SOURCE: ISO 3744:2010, 3.4]
3.8
sound intensity

I


Ip=⋅u
where
ISO 3740:2019(E)
p is the sound pressure, in Pa;

u is the sound particle velocity, in m/s.


Note 1 to entry: u and I are vectorial quantities.
3.9
vibratory velocity
v
root-mean square (RMS) value of the component of the velocity of a vibrating surface in the direction
normal to the surface
Note 1 to entry: In ISO/TS 7849-1, the vibratory velocity is applied with an A-weighting, denoted v .
A
[SOURCE: ISO 7849-1:2009, 3.3, modified — Former Note 1 to entry deleted, expression "In ISO/
TS 7849-1" used for clarification instead of "In this part of ISO/TS 7849" in former Note 2, now Note 1.]
3.10
vibratory velocity level
L
v
ten times the logarithm to the base 10 of the ratio of the square of the RMS value of the vibratory
velocity, v, to the square of a reference value, v , expressed in decibels:
v
L =10lg dB
v
v
where
v is the RMS value of the vibratory velocity, in metres per second;
–8
v is the reference value for the velocity and is equal to 5 × 10 m/s.
Note 1 to entry: For airborne and structure vibration generated sound, the reference value, v = 50 nm/s has the
−5 −12
property that it leads, together with p = 2 × 10 Pa, to the reference value of the intensity level I = 1 × 10 W/
0 0
m and to a characteristic impedance of air of p /v = 400 Pa·s/m.
0 0
Note 2 to entry: In ISO/TS 7849-1, the vibratory velocity level is applied as A-weighted vibratory velocity level,
2 2
L , by substituting v for the A-weighted RMS v in ISO/TS 7849-1:2009, Formula (6).
vA A
−9
Note 3 to entry: In ISO 1683, two reference values for the velocity level are mentioned: v = 10 m/s and
−8
5 × 10 m/s. The latter is intended for cases of airborne and structure vibration generated sound and is therefore
−9
used in ISO/TS 7849-1 and ISO/TS 7849-2. A choice of v = 10 m/s results in a vibratory velocity level which is
−9
34 dB higher than the level used in both parts of ISO/TS 7849. Therefore, if v = 10 m/s is used, subtract 34 dB
from the right-hand sides of the first formula in 3.10.
3.11
radiation factor
ε
factor expressing the efficiency of airborne sound power (3.2) radiation from the vibrating surface
Note 1 to entry: See ISO/TS 7849-1:2009, 4.4.1 to 4.4.4.
3.12
background noise
noise from all sources other than the noise source under test
Note 1 to entry: Background noise includes contributions from airborne sound, noise from structure-borne
vibration, and electrical noise in the instrumentation.
[SOURCE: ISO 3744:2010, 3.15]
4 © ISO 2019 – All rights reserved

ISO 3740:2019(E)
3.13
background noise level
sound pressure level (3.5) measured when the source under test is not operating
Note 1 to entry: It is expressed in decibels.
3.14
extraneous vibratory velocity level
vibratory velocity level (3.10) caused by all sources other than the source under test
Note 1 to entry: Extraneous vibratory velocity levels originate, for example, from coupled assemblies.
[SOURCE: ISO/TS 7849-1:2009, 3.9]
3.15
background noise correction
K
correction applied to the mean (energy average) of the time-averaged sound pressure levels (3.6) over
all the microphone positions on the measurement surface, to account for the influence of background
noise (3.12)
Note 1 to entry: Background noise correction is expressed in decibels.
Note 2 to entry: The background noise correction is frequency dependent; the correction of a frequency band is
denoted K , where f denotes the relevant center frequency, and that in the case of A-weighting is denoted K .
1f 1A
[SOURCE: ISO 3744:2010, 3.16]
3.16
environmental correction
K
correction applied to the mean (energy average) of the time-averaged sound pressure levels (3.6) over
all microphone positions on the measurement surface, to account for the influence of reflected or
absorbed sound
Note 1 to entry: Environmental correction is expressed in decibels.
Note 2 to entry: The environmental correction is frequency dependent; the correction in the case of a frequency
band is denoted K , where f denotes the relevant mid-band frequency, and that in the case of A-weighting is
2f
denoted K .
2A
Note 3 to entry: In general, the environmental correction depends on the area of the measurement surface and
usually K increases with S.
[SOURCE: ISO 3744:2010, 3.17]
3.17
systematic deviation
Δ
sy
deviation to account for a systematic difference between sound power levels (3.3) obtained using basic
standards based on different physical rules
Note 1 to entry: Δ is not covered in the basic standards. See 4.4 and Annex C.
sy
Note 2 to entry: Δ describes specifically the systematic deviation between the sound power level yielded
sy,pI
by the intensity method, L , compared with the result from free field sound pressure measurements, L :
W,I W,p
Δ = L – L ; otherwise Δ is also designated as near field error.
sy,pI W,p W,I sy,pI
Note 3 to entry: Systematic deviations can also appear when environmental correction, K , is determined
according to different procedures from the basic standards.
ISO 3740:2019(E)
3.18
background noise index
ΔL
p
index denoting the difference, in decibels, between the sound pressure levels (3.5) from the noise source
under test in operation and the sound pressure levels of the background noise (3.12), both measured
using an array of microphone positions over the measurement surface
3.19
dynamic capability index
L
d
index given by
LK=−δ
d pI
where
is the pressure-residual intensity index, in decibels;
δ
pI
K is the bias error, in decibels.
Note 1 to entry: The dynamic capability index is expressed in decibels.
Note 2 to entry: The dynamic capability index describes the quality of the intensity measurement system to
suppress unwanted background noise. It is used to check the attainment of the desired accuracy level, where K is
selected to be 10 dB for grade 1 and 2 measurements and 7 dB for grade 3 measurements.
3.20
standard deviation of reproducibility of the method
σ
R0
uncertainty associated with a sound power (3.2) measurement method excluding the uncertainty due to
the instability of the sound power of the source under test
Note 1 to entry: σ is determined from round robin tests on an extreme stable source. It does not include
R0
uncertainty components like σ and Δ and consequently does not represent the total uncertainty.
omc sy
3.21
standard deviation due to operating and mounting conditions of the sound source
σ
omc
uncertainty associated with the instability of the operating and mounting conditions for the particular
source under test
3.22
total standard deviation
σ
tot
square root of the sum of the squares of the standard deviation of reproducibility of the method (3.20)
and the standard deviation due to operating and mounting conditions (3.21)
σσ=+σ
totoR0 mc
3.23
accuracy grade
grade characterising three different classes of uncertainty in determining sound power levels (3.3)
based on the standard deviations of reproducibility of the method, σ (3.20)
R0
Note 1 to entry: The grade classification provides an indication of the required measurement effort.
Note 2 to entry: It is described by typical upper bound values.
Note 3 to entry: σ does not include uncertainty components like σ and Δ and consequently does not
R0 omc sy
represent the total uncertainty.
6 © ISO 2019 – All rights reserved

ISO 3740:2019(E)
3.24
expanded measurement uncertainty
U
characteristic value identifying a range around the measurement result or calculation within which an
estimate of values is expected to lie
4 Sound power level
4.1 Basic information
The sound power level characterizes the mean airborne acoustic energy flow from the source into
the environment for a given mounting and operating condition and represents an intrinsic acoustic
characteristic of the source that is independent of the environment in which it is installed. It is often
denoted as an A-weighted sound power level, L , in dB.
WA
4.2 Reasons for the determination of sound power levels
Example situations where the A-weighted sound power level of a machine, equipment and product can
be of interest are:
— manufacturer noise emission declarations in the instructions and the sales literature according to
regulations for machinery safety;
— customer need for input to sound exposure prediction models which can support legal requirements
for carrying out a noise exposure risk assessment;
— customer need for comparison with the state of the art of noise emission, for comparing the data of
competing machinery, equipment and products to support the “Buy Quiet” objective;
— checking the noise emission level of machinery, equipment and products in specifications regardless
of the environment in which they operate.
4.3 Basic procedures for determining sound power levels
Sound pressure, sound intensity and vibratory velocity level measurements form the basis of different
procedures to determine sound power level. These procedures include
— evaluation of the spatial mean-squared sound pressure built up in highly reflective environments
(ISO 3741, ISO 3743-1, ISO 3743-2);
— comparison of the sound pressure levels in octave frequency bands of a noise source under test with
those of a calibrated reference sound source (ISO 3747);
— evaluation of the flow of sound energy by a direct measurement of the sound intensity (ISO 9614-1,
ISO 9614-2, ISO 9614-3) near the source or the free field approximation of the intensity through
measurement of the squared sound pressure (ISO 3744, ISO 3745, ISO 3746) emitted by the source,
both measurements carried out on an enveloping surface;
— evaluation of the partial flow of airborne sound energy emitted by vibrating solid structures of the
machine, using measurements of the vibratory velocity over the surface of vibrating solid structures
(ISO/TS 7849-1, ISO/TS 7849-2).
Microphones used to measure the sound pressure level at specific positions around the source under
test measure the sum of the direct sound from the source and the contributions from other sound
sources in the measurement room plus the sound which is reflected by walls, floor, ceiling and obstacles.
Therefore, corrections to cope with these influences are required in practice. These are the background
noise correction, K , and the environmental correction, K . Please refer to Annex D for examples of
1 2
practical applications of ISO 3744 and ISO 3746.
ISO 3740:2019(E)
In contrast to sound pressure measurements, sound intensity measurements used for determining the
sound power level are less sensitive to steady state background noise and the environment, provided
that the capacity of the measurement instrument is not exceeded. Background noise that fluctuates
cyclically needs an adequately longer integration time at each measurement position. In principle, this
measurement approach provides a measure of the sound power radiated directly into the air by all
sources located within the enclosing surface, and excludes sound radiated by sources, including mirror
sources resulting from sound reflections, located outside the enveloping surface.
Owing to differences in meteorological conditions, sound power level measurements at different test
facilities can yield considerably different results. For example, measurements of sound power level at
high altitude cause an underestimate of the sound power level when compared to measurements at
sea level. Therefore, many of the above mentioned measurement procedures except ISO 9614-1 and
ISO 9614-2 include corrections to allow for any differences that can exist between the meteorological
conditions under which the tests are conducted and reference meteorological conditions. ISO/TS 7849-1
and ISO/TS 7849-2 yield by definition the sound power level under reference meteorological conditions.
4.4 Quality of determined sound power levels
Sound power levels determined according to different methods include different random and systematic
deviations. Random deviations are clearly dealt with in the present sound power measurement
standards but systematic ones are not addressed.
Assuming a repeated application of the same measurement standard, a randomly distributed spread of
results can be expected. These deviations are caused
— by an inadequate approximation in practice of the relevant physical relations on which the
measurement method is based, represented by σ , and
R0
— by inaccuracies when adjusting the machine, equipment, product to the predefined operating and
mounting conditions, e.g. those specified in the relevant noise test code, represented by σ .
omc
For the set of basic International Standards, three different classes of accuracy grades (see 3.24) define
the quality of the determined sound power level value. These are:
— accuracy grade 1, called precision grade,
— accuracy grade 2, called engineering grade, and
— accuracy grade 3 ,called survey grade.
These correspond to different measurement efforts and conditions, e.g. characteristics of the
measurement environment or background noise.
For legal reasons or contractual ones between a manufacturer and a customer, minimum requirements
on the accuracy of the measured sound power level can be stated in the instructions, in sales catalogues
containing performance data or in sales contracts. For most uses, the application of methods providing
engineering grade (grade 2) results is expected to be satisfactory.
It is common to include information about the uncertainty of the determined quantity when providing
measurement results. In practice, this is done through the expanded measurement uncertainty, U.
Annex C provides detailed information on measurement uncertainty for sound power level determined
according to one of the methods described in this document.
4.5 Noise emission declaration
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,
equipment and products when preparing noise emission declarations according to noise test codes.
Formats for noise emission declarations and procedures for declaration and verification are presented
in ISO 4871.
8 © ISO 2019 – All rights reserved

ISO 3740:2019(E)
5 Selection of the most appropriate method in the set of standards
5.1 Methods and quantities to be measured and determined
Tables 1, 2 and 3 give a rather detailed overview of the available basic International Standards
describing methods for the determination of the airborne sound power level, either A-weighted or in
frequency bands. The tables distinguish between those methods which are based on sound pressure
level measurements (ISO 3741 to ISO 3747), sound intensity measurements (ISO 9614-1 to ISO 9614-3)
and vibratory velocity measurements (ISO/TS 7849-1 and ISO/TS 7849-2). The ISO/TS 7849 methods
only consider that part of the airborne sound power level which is caused by vibrating solid structures
of the source under test and therefore exclude aerodynamically generated noise. Therefore, they will
normally only be used in practice when other methods cannot reliably be applied or for machinery
development purposes.
The sound power levels determined may be time-averaged, frequency-weighted, in frequency bands or
time-weighted. The most commonly used frequency weighting is A-weighting.
Annex A provides an overview of the main facts and requirements of the basic International Standards
for determining sound power levels of machines, equipment and products.
5.2 Considerations affecting the selection of a measurement method
There are many factors influencing a proper selection of basic International Standards for determining
sound power level. Figure 1 provides a guide based on the selection via the different parameters and
environment to be considered.
ISO 3740:2019(E)
Figure 1 — Flowchart guiding the selection of appropriate International Standards for the
determination of sound power levels
Some important parameters to consider because they influence the selection of a suitable method are:
— the existence of a relevant noise test code or procedure making reference to one or more basic
standards;
10 © ISO 2019 – All rights reserved

ISO 3740:2019(E)
— the kind of sound power level desired, i.e. the total radiated airborne sound power level or only that
portion caused by radiated structural vibrations;
— the type of sound power level desired (frequency-weighted or in frequency bands, frequency range
of interest);
— the grade of accuracy desired;
— the measurement environment to be used for the test (in situ, essential free field, laboratory
rooms or special test rooms such as free field or reverberant rooms), together with the size and
transportability of the source under test that determine the practicability of setting up and operating
the source in an acoustical test laboratory;
— the background noise level;
— the character of the noise produced by the source (e.g. broad-band, narrow-band, discrete-frequency;
steady, non-steady, impulsive);
— the acoustical instrumentation available (sound pressure level meters, sound intensity measurement
systems);
— further acoustical information desired (e.g. directivity of source, time history of the generated sound).
In contrast to Tables 1 and 2, Table A.1 gives a more restricted overview on the set of standards
concentrating on aspects like the grade of accuracy of the method, the required test environment, the
volume of the source, the character of the noise and the obtainable sound power levels.
NOTE 1 The preferred grade of accuracy for the purpose of preparing a noise emission declaration is
engineering (grade 2).
NOTE 2 All standards within a specific grade imply the same level of accuracy apart from systematic
deviations existing between results of different measurement methods.
ISO 3740:2019(E)
12 © ISO 2019 – All rights reserved
Table 1 — Overview of International Standards for the determination of sound power levels of machines, equipment and products using
sound pressure
Methods based on sound pressure level measurements
Parameter ISO 3741 ISO 3743-1 ISO 3743-2 ISO 3744 ISO 3745 ISO 3746 ISO 3747
Grade of accu- Engineering or
Precision Engineering Engineering Engi
...