EN ISO 3744:2010

SLOVENSKI STANDARD
01-december-2010
1DGRPHãþD
SIST EN ISO 3744:2009
$NXVWLND8JRWDYOMDQMHUDYQL]YRþQLKPRþLYLURYKUXSD]PHUMHQMHP]YRþQHJD
WODND,QåHQLUVNDPHWRGDYSUHWHåQRSURVWHPSROMXQDGRGERMQRUDYQLQR,62

Acoustics - Determination of sound power levels and sound energy levels of noise
sources using sound pressure - Engineering methods for an essentially free field over a
reflecting plane (ISO 3744:2010)
Akustik - Bestimmung der Schallleistungs- und der Schallenergiepegel von
Geräuschquellen aus Schalldruckmessungen - Hüllflächenverfahren der
Genauigkeitsklasse 2 für ein im Wesentlichen freies Schallfeld über einer reflektierenden
Ebene (ISO 3744:2010)
Acoustique - Détermination des niveaux de puissance et d'énergie acoustique émis par
les sources de bruit à partir de la pression acoustique - Méthodes d'expertise pour des
conditions approchant celles du champ libre sur plan réfléchissant (ISO 3744:2010)
Ta slovenski standard je istoveten z: EN ISO 3744:2010
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 3744
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2010
ICS 17.140.01 Supersedes EN ISO 3744:2009
English Version
Acoustics - Determination of sound power levels and sound
energy levels of noise sources using sound pressure -
Engineering methods for an essentially free field over a
reflecting plane (ISO 3744:2010)
Acoustique - Détermination des niveaux de puissance et Akustik - Bestimmung der Schallleistungs- und der
d'énergie acoustiques émis par les sources de bruit à partir Schallenergiepegel von Geräuschquellen aus
de la pression acoustique - Méthodes d'expertise pour des Schalldruckmessungen - Hüllflächenverfahren der
conditions approchant celles du champ libre sur plan Genauigkeitsklasse 2 für ein im Wesentlichen freies
réfléchissant (ISO 3744:2010) Schallfeld über einer reflektierenden Ebene (ISO
3744:2010)
This European Standard was approved by CEN on 14 August 2010.

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, Croatia, 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
© 2010 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 3744:2010: E
worldwide for CEN national Members.

Contents Page
Foreword .3
Annex ZA .4

Foreword
The text of ISO 3744:2010 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 3744:2010 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 April 2011, and conflicting national standards shall be withdrawn at the
latest by April 2011.
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 3744:2009.
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 EU Directive.
For relationship with EU Directive, see informative Annex ZA, which is an integral part 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, Croatia, 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 3744:2010 has been approved by CEN as a EN ISO 3744:2010 without any modification.
Annex ZA
(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 one 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 products falling
within the scope of this standard.
INTERNATIONAL ISO
STANDARD 3744
Third edition
2010-10-01
Acoustics — Determination of sound
power levels and sound energy levels of
noise sources using sound pressure —
Engineering methods for an essentially
free field over a reflecting plane
Acoustique — Détermination des niveaux de puissance et d'énergie
acoustiques émis par les sources de bruit à partir de la pression
acoustique — Méthodes d'expertise pour des conditions approchant
celles du champ libre sur plan réfléchissant

Reference number
ISO 3744:2010(E)
©
ISO 2010
ISO 3744:2010(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

©  ISO 2010
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2010 – All rights reserved

ISO 3744:2010(E)
Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Normative references.2
3 Terms and definitions .2
4 Test environment.8
5 Instrumentation .11
6 Definition, location, installation, and operation of noise source under test.12
7 Reference box and measurement surface.14
8 Determination of sound power levels and sound energy levels .18
9 Measurement uncertainty.26
10 Information to be recorded.29
11 Test report.31
Annex A (normative) Qualification procedures for the acoustic environment .32
Annex B (normative) Microphone arrays on a hemispherical measurement surface .37
Annex C (normative) Microphone arrays on a parallelepiped measurement surface .44
Annex D (informative) Microphone arrays on a cylindrical measurement surface.55
Annex E (normative) Calculation of A-weighted sound power levels and A-weighted sound
energy levels from frequency band levels.59
Annex F (normative) Alternative microphone array on a hemispherical measurement surface for
direct measurements of A-weighted sound pressure levels .61
Annex G (normative) Sound power level and sound energy level under reference meteorological
conditions.64
Annex H (informative) Guidelines on the development of information on measurement uncertainty .66
Bibliography.77

ISO 3744:2010(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 2.
The main task of technical committees is to prepare International Standards. 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 document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 3744 was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.
This third edition of ISO 3744 cancels and replaces the second edition (ISO 3744:1994) and ISO 4872:1978,
of which it constitutes a merger and a technical revision.
iv © ISO 2010 – All rights reserved

ISO 3744:2010(E)
Introduction
[2] [6]
This International Standard is one of the series ISO 3741 to ISO 3747 , which specify various methods for
determining the sound power levels and sound energy levels of noise sources including machinery, equipment
[1]
and their sub-assemblies. General guidelines to assist in the selection are provided in ISO 3740 . The
selection depends on the environment of the available test facility and on the precision of the sound power
level or sound energy level values required. It may be necessary to establish a noise test code (see
ISO 12001) for the individual noise source in order to select the appropriate sound measurement surface and
[2] [6]
microphone array from among those allowed in each member of the ISO 3741 to ISO 3747 series, and to
give requirements on test unit mounting, loading and operating conditions under which the sound power levels
or sound energy levels are to be obtained. The sound power emitted by a given source into the test
environment is calculated from the mean square sound pressure that is measured over a hypothetical
measurement surface enclosing the source, and the area of that surface. The sound energy for a single sound
event is calculated from this sound power and the time over which it existed.
The methods specified in this International Standard permit the determination of the sound power level and
the sound energy level in frequency bands optionally with frequency A-weighting applied.
[2]
For applications where greater accuracy is required, reference can be made to ISO 3745, ISO 3741 or
[13]-[15]
ISO 9614 . If the relevant criteria for the measurement environment specified in this International
[13]-[15]
Standard are not met, it might be possible to refer to another standard from this series, or to ISO 9614 .
This International Standard describes methods of accuracy grade 2 (engineering grade) as defined in
ISO 12001, when the measurements are performed in a space that approximates an acoustically free field
over a reflecting plane. Such an environment can be found in a specially designed room, or within industrial
buildings or outdoors. Ideally, the test source should be mounted on a sound-reflecting plane located in a
large open space. For sources normally installed on the floor of machine rooms, corrections are defined to
account for undesired reflections from nearby objects, walls and the ceiling, and for the residual background
noises that occur there.
INTERNATIONAL STANDARD ISO 3744:2010(E)

Acoustics — Determination of sound power levels and sound
energy levels of noise sources using sound pressure —
Engineering methods for an essentially free field over a
reflecting plane
1 Scope
1.1 General
This International Standard specifies methods for determining the sound power level or sound energy level of
a noise source from sound pressure levels measured on a surface enveloping the noise source (machinery or
equipment) in an environment that approximates to an acoustic free field near one or more reflecting planes.
The sound power level (or, in the case of noise bursts or transient noise emission, the sound energy level)
produced by the noise source, in frequency bands or with A-weighting applied, is calculated using those
measurements.
NOTE Differently shaped measurement surfaces can yield differing estimates of the sound power level of a given
noise source and an appropriately drafted noise test code (see ISO 12001) gives detailed information on the selection of
the surface.
1.2 Types of noise and noise sources
The methods specified in this International Standard are suitable for all types of noise (steady, non-steady,
fluctuating, isolated bursts of sound energy, etc.) defined in ISO 12001.
This International Standard is applicable to all types and sizes of noise source (e.g. stationary or slowly
moving plant, installation, machine, component or sub-assembly), provided the conditions for the
measurements can be met.
NOTE It is possible that the conditions for measurements given in this International Standard are impracticable for
very tall or very long sources such as chimneys, ducts, conveyors and multi-source industrial plants. A noise test code for
the determination of noise emission of specific sources can provide alternative methods in such cases.
1.3 Test environment
The test environments that are applicable for measurements made in accordance with this International
Standard can be located indoors or outdoors, with one or more sound-reflecting planes present on or near
which the noise source under test is mounted. The ideal environment is a completely open space with no
bounding or reflecting surfaces other than the reflecting plane(s) (such as that provided by a qualified hemi-
anechoic chamber), but procedures are given for applying corrections (within limits that are specified) in the
case of environments that are less than ideal.
1.4 Measurement uncertainty
Information is given on the uncertainty of the sound power levels and sound energy levels determined in
accordance with this International Standard, for measurements made in limited bands of frequency and with
frequency A-weighting applied. The uncertainty conforms to ISO 12001:1996, accuracy grade 2 (engineering
grade).
ISO 3744:2010(E)
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 3382-2, Acoustics — Measurement of room acoustic parameters — Part 2: Reverberation time in ordinary
rooms
ISO 3745, Acoustics — Determination of sound power levels and sound energy levels of noise sources using
sound pressure — Precision methods for anechoic test rooms and hemi- anechoic test rooms
ISO 5725 (all parts), Accuracy (trueness and precision) of measurement methods and results
ISO 6926, Acoustics — Requirements for the performance and calibration of reference sound sources for the
determination of sound power levels
ISO 12001:1996, Acoustics — Noise emitted by machinery and equipment — Rules for the drafting and
presentation of a noise test code
ISO/IEC Guide 98-3, Uncertainty in measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
IEC 60942:2003, Electroacoustics — Sound calibrators
IEC 61260:1995, Electroacoustics — Octave-band and fractional-octave-band filters
IEC 61672-1:2002, Electroacoustics — Sound level meters — Part 1: Specifications
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
sound pressure
p
difference between instantaneous pressure and static pressure
[21]
NOTE 1 Adapted from ISO 80000-8:2007 , 8-9.2.
NOTE 2 Sound pressure is expressed in pascals.
3.2
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 = 10 lg dB (1)
p
p
where the reference value, p , is 20 µPa
[20]
[ISO/TR 25417:2007 , 2.2]
2 © ISO 2010 – All rights reserved

ISO 3744:2010(E)
NOTE 1 If specific frequency and time weightings 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 pressure level.
pA
[21]
NOTE 2 This definition is technically in accordance with ISO 80000-8:2007 , 8-22.
3.3
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 a reference value,
1 2
p , expressed in decibels
t
⎡⎤2
⎢⎥
pt()dt
∫
⎢⎥
T
t
⎢⎥1
L = 10 lg dB (2)
pT,
⎢⎥2
p
⎢⎥
⎢⎥
⎢⎥
⎣⎦
where the reference value, p , is 20 µPa
NOTE 1 In general, the subscript “T” is omitted since time-averaged sound pressure levels are necessarily determined
over a certain measurement time interval.
NOTE 2 Time-averaged sound pressure levels are often A-weighted, in which case they are denoted by L , which is
pA,T
usually abbreviated to L .
pA
[20]
NOTE 3 Adapted from ISO/TR 25417:2007 , 2.3.
3.4
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
2 0
t
⎡⎤
⎢⎥
pt()dt
∫
⎢⎥
t
⎢⎥1
L = 10 lg dB (3)
E
⎢⎥
E
⎢⎥
⎢⎥
⎢⎥
⎣⎦
2 −10 2
where the reference value, E , is (20 µPa) s = 4 × 10 Pa s
⎡⎤
T
NOTE 1 This quantity can be obtained by L +10 lg dB , where T = 1 s.
⎢⎥
pT,
T
⎣⎦
NOTE 2 When used to measure sound immission, this quantity is usually called “sound exposure level”
[20]
(see ISO/TR 25417:2007 ).
ISO 3744:2010(E)
3.5
measurement time interval
T
portion or a multiple of an operational period or operational cycle of the noise source under test for which the
time-averaged sound pressure level is determined
NOTE Measurement time interval is expressed in seconds.
3.6
acoustic free field
sound field in a homogeneous, isotropic medium free of boundaries
NOTE In practice, an acoustic free field is a field in which the influence of reflections at the boundaries or other
disturbing objects is negligible over the frequency range of interest.
3.7
acoustic free field over a reflecting plane
acoustic free field in the half-space above an infinite reflecting plane in the absence of any other obstacles
3.8
reflecting plane
sound reflecting planar surface on which the noise source under test is located
3.9
frequency range of interest
for general purposes, the frequency range of octave bands with nominal mid-band frequencies from 125 Hz to
8 000 Hz (including one-third octave bands with mid-band frequencies from 100 Hz to 10 000 Hz)
NOTE For special purposes, the frequency range can be extended or reduced, provided that the test environment
and instrument specifications are satisfactory for use over the modified frequency range. Changes to the frequency range
of interest are included in the test report.
3.10
reference box
hypothetical right parallelepiped terminating on the reflecting plane(s) on which the noise source under test is
located, that just encloses the source including all the significant sound radiating components and any test
table on which the source is mounted
NOTE If required, the smallest possible test table can be used for compatibility with emission sound pressure
[18]
measurements at bystander positions in accordance with, for example, ISO 11201 .
3.11
characteristic source dimension
d
O
distance from the origin of the co-ordinate system to the farthest corner of the reference box
NOTE Characteristic source dimension is expressed in metres.
3.12
measurement distance
d
distance from the reference box to a parallelepiped measurement surface
NOTE Measurement distance is expressed in metres.
3.13
measurement radius
r
radius of a hemispherical, half-hemispherical or quarter-hemispherical measurement surface
NOTE Measurement radius is expressed in metres.
4 © ISO 2010 – All rights reserved

ISO 3744:2010(E)
3.14
measurement surface
hypothetical surface of area, S, on which the microphone positions are located at which the sound pressure
levels are measured, enveloping the noise source under test and terminating on the reflecting plane(s) on
which the source is located
3.15
background noise
noise from all sources other than the noise source under test
NOTE Background noise includes contributions from airborne sound, noise from structure-borne vibration, and
electrical noise in the instrumentation.
3.16
background noise correction
K
correction applied to the mean (energy average) of the time-averaged sound pressure levels over all the
microphone positions on the measurement surface, to account for the influence of background noise
NOTE 1 Background noise correction is expressed in decibels.
NOTE 2 The background noise 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 denoted K .
1f 1A
3.17
environmental correction
K
correction applied to the mean (energy average) of the time-averaged sound pressure levels over all the
microphone positions on the measurement surface, to account for the influence of reflected or absorbed
sound
NOTE 1 Environmental correction is expressed in decibels.
NOTE 2 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 denoted K .
2f 2A
NOTE 3 In general, the environmental correction depends on the area of the measurement surface and usually K
increases with S.
3.18
surface time-averaged sound pressure level
L
p
mean (energy average) of the time-averaged sound pressure levels over all the microphone positions, or
traverses, on the measurement surface, with the background noise correction, K , and the environmental
correction, K , applied
NOTE Surface time-averaged sound pressure level is expressed in decibels.
3.19
surface single event time-integrated sound pressure level
L
E
mean (energy average) of the single event time-integrated sound pressure levels at all the microphone
positions, or traverses, on the measurement surface, with the background noise correction, K , and the
environmental correction, K , applied
NOTE Surface single event time-integrated sound pressure level is expressed in decibels.
ISO 3744:2010(E)
3.20
sound power
P
through a surface, product of the sound pressure, p, and the component of the particle velocity, u , at a point
n
on the surface in the direction normal to the surface, integrated over that surface
[21]
[ISO 80000-8:2007 , 8-16]
NOTE 1 Sound power is expressed in watts.
NOTE 2 The quantity relates to the rate per time at which airborne sound energy is radiated by a source.
3.21
sound power level
L
W
ten times the logarithm to the base 10 of the ratio of the sound power of a source, P, to a reference value, P ,
expressed in decibels
P
L = 10 lg dB (4)
W
P
where the reference value, P , is 1 pW
NOTE 1 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
[21]
NOTE 2 This definition is technically in accordance with ISO 80000-8:2007 , 8-23.
[20]
[ISO/TR 25417:2007 , 2.9]
3.22
sound energy
J
integral of the sound power, P, over a stated time interval of duration T (starting at t and ending at t )
1 2
t
J = Pt()dt (5)
∫
t
NOTE 1 Sound energy is expressed in joules.
NOTE 2 The quantity is particularly relevant for non-stationary, intermittent sound events.
[20]
[ISO/TR 25417:2007 , 2.10]
3.23
sound energy level
L
J
ten times the logarithm to the base 10 of the ratio of the sound energy, J, to a reference value, J , expressed
in decibels
J
L = 10 lg dB (6)
J
J
where the reference value, J , is 1 pJ
6 © ISO 2010 – All rights reserved

ISO 3744:2010(E)
NOTE 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 energy level.
JA
[20]
[ISO/TR 25417:2007 , 2.11]
3.24
apparent directivity index
*
D
Ii
measure of the extent to which a noise source under test radiates sound in the direction of the ith microphone
position on a measurement surface, relative to the mean sound radiation over the measurement surface
*
⎡⎤
′
D=−LL −K (7)
Iipi(ST) p(ST) 1
⎣⎦
where
L is the background noise-corrected time-averaged (or single event time-integrated) sound
pi(ST)
pressure level for the ith microphone position on the measurement surface, with the noise
source under test (ST) in operation, in decibels;
L′ is the mean (energy average) time-averaged (or single event time-integrated) sound pressure
p(ST)
level over all the microphone positions on the measurement surface for the noise source under
test, in decibels;
K is the background noise correction, in decibels.
NOTE 1 Apparent directivity index is expressed in decibels.
NOTE 2 The apparent directivity index is determined using measured sound pressure levels from the noise source
under test corrected for background noise, but with no corrections for the influence of the acoustic environment.
3.25
apparent surface sound pressure level non-uniformity index
*
V
I
measure of the variability of measured sound pressure levels over the measurement surface
N
M
*
⎡⎤
VL=−L (8)
∑ pi(ST) pav
Ι ⎣⎦
N − 1
M
i=1
where
L is the background noise-corrected time-averaged (or single event time-integrated) sound
pi(ST)
pressure level for the ith microphone position on the measurement surface, with the noise
source under test (ST) in operation, in decibels;
L is the arithmetic average of the background noise-corrected time-averaged (or single event
pav
time-integrated) sound pressure levels over all the microphone positions on the measurement
surface for the noise source under test, in decibels;
N is the number of microphone positions.
M
NOTE 1 Apparent surface sound pressure level non-uniformity index is expressed in decibels.
*
NOTE 2 When V is determined over the specific measurement surface given by the measurement radius, r, or
I
* *
measurement distance, d, the value is denoted V or V , respectively.
Ir Id
ISO 3744:2010(E)
NOTE 3 The apparent surface sound pressure level non-uniformity index is determined using measured sound
pressure levels from the noise source under test, corrected for background noise, but with no corrections for the influence
of the acoustic environment.
4 Test environment
4.1 General
The test environments that are applicable for measurements in accordance with this International Standard
are:
a) a laboratory room or a flat outdoor area which is adequately isolated from background noise (see 4.2) and
which provides an acoustic free field over a reflecting plane;
b) a room or a flat outdoor area which is adequately isolated from background noise (see 4.2) and in which
an environmental correction can be applied to allow for a limited contribution from the reverberant field to
the sound pressures on the measurement surface.
Environmental conditions having an adverse effect on the microphones used for the measurements
(e.g. strong electric or magnetic fields, wind, impingement of air discharge from the noise source being tested,
high or low temperatures) shall be avoided. The instructions of the manufacturer of the measuring
instrumentation regarding adverse environmental conditions shall be followed.
In an outdoor area, care shall be taken to minimize the effects of adverse meteorological conditions
(e.g. temperature, humidity, wind, precipitation) on the sound propagation and on sound generation over the
frequency range of interest or on the background noise during the course of the measurements.
When a reflecting surface is not a ground plane or is not an integral part of a test room surface, particular care
should be exercised to ensure that the plane does not radiate any appreciable sound due to vibrations.
4.2 Criteria for background noise
4.2.1 Relative criteria
4.2.1.1 General
The time-averaged sound pressure level of the background noise measured and averaged (see 8.2.2) over
the microphone positions, or traverses, on the measurement surface, shall be at least 6 dB, and preferably
more than 15 dB, below the corresponding uncorrected time-averaged sound pressure level of the noise
source under test when measured in the presence of this background noise. For measurements in frequency
bands, this requirement shall be met in each frequency band within the frequency range of interest.
If this requirement is met, the background noise criteria of this International Standard are satisfied.
NOTE 1 A similar criterion is applied to single event sound pressure levels: the measurement time interval for the time
average is the same as the measurement time interval associated with the single event.
NOTE 2 The noise associated with the microphone traversing mechanism, if one is used for the measurements, is
considered to be part of the background noise. In such cases, the background noise is measured with the traversing
mechanism operating.
4.2.1.2 Frequency band measurements
The requirements of 4.2.1.1 may not be achievable in all frequency bands, even when the background noise
levels in the test room are extremely low and well controlled. Therefore, any band within the frequency range
of interest in which the A-weighted sound power level or sound energy level of the noise source under test is
at least 15 dB below the highest A-weighted band sound power level may be excluded from the frequency
range of interest for the purposes of determining compliance with the criteria for background noise.
8 © ISO 2010 – All rights reserved

ISO 3744:2010(E)
4.2.1.3 A-weighted measurements
If the A-weighted sound power level or sound energy level is to be determined from frequency band levels and
reported, the following steps shall be followed to determine whether this quantity meets the background noise
criteria of this International Standard:
a) the A-weighted sound power level or sound energy level is computed in accordance with the procedures
in this International Standard using the data from every frequency band within the frequency range of
interest;
b) the computation is repeated, but excluding those bands for which ∆L < 6 dB.
p
If the difference between these two levels is less than 0,5 dB, the A-weighted sound power level or sound
energy level determined from the data for all bands may be considered as conforming to the background
noise criteria of this International Standard.
NOTE If it is necessary to make measurements where the difference between the sound pressure levels of the
[13] [14]
background noise and the source together with the background noise is less than 6 dB, ISO 9614-1 or ISO 9614-2
can be used to give results of accuracy grade 2.
4.2.2 Absolute criteria
If it can be demonstrated that the background noise levels in the test room at the time of the measurements
are less than or equal to those given in Table 1 for all bands within the frequency range of interest, the
measurements can be taken as having met the background noise requirements of this International Standard,
even if the 6 dB requirement (see 4.2.1.1) is not met for all bands. It can be assumed that the source emits
little or no measurable noise in these frequency bands, and that the data reported represent an upper bound
to the sound power level in these bands.
In the case where some of the measured (either time-averaged or single event time-integrated) levels from the
source under test are less than or equal to those given in Table 1, the frequency range of interest may be
restricted to a contiguous range of frequencies that includes both the lowest and highest frequencies at which
the sound pressure level from the noise source exceeds the corresponding value in Table 1. In such cases,
the applicable frequency range of interest shall be reported.
4.2.3 Statement of non-conformity with criteria
If neither the relative criteria of 4.2.1 nor the absolute criteria in 4.2.2 are met, the report shall clearly state that
the background noise requirements of this International Standard have not been met, and, in the case of
frequency band measurements, shall identify the particular frequency bands that do not meet the criteria.
Furthermore, the report shall not state or imply that the measurements have been made “in full conformity”
with this International Standard.
ISO 3744:2010(E)
Table 1 — Maximum background noise levels in test room for absolute criteria
One-third-octave mid-band Maximum band sound
frequency pressure level
Hz dB
50 44
63 38
80 32
100 27
125 22
160 16
200 13
250 11
315 9
400 8
500 7
630 7
800 7
1 000 7
1 250 7
1 600 7
2 000 7
2 500 8
3 150 8
4 000 8
5 000 8
6 300 8
8 000 12
10 000 14
12 500 11
16 000 46
20 000 46
4.3 Criterion for acoustic adequacy of test environment
4.3.1 General
A test room shall provide a measurement surface that lies inside a sound field that is essentially free of
undesired sound reflections from the room boundaries or nearby objects (apart from the floor).
As far as is practicable, the test environment shall be free from reflecting objects other than the reflecting
plane(s).
10 © ISO 2010 – All rights reserved

ISO 3744:2010(E)
NOTE 1 An object in the proximity of the noise source under test can be considered to be sound reflecting if its width
(e.g. diameter of a pole or supporting member) exceeds one-tenth of its distance from the reference box.
The reflecting plane(s) shall extend at least 0,5 m beyond the projection of the measurement surface on the
plane(s). The sound absorption coefficient of the reflecting plane(s) shall be less than 0,1 over the frequency
range of interest.
NOTE 2 Smooth concrete or smooth sealed asphalt surface(s) are generally satisfactory.
Annex A specifies procedures for determining the magnitude of the environmental correction, K , to account
for deviations of the test environment from the ideal condition. Measurements in accordance with this
International Standard are only valid where K u 4 dB (see 4.3.2, Reference [25]).
2A
[3][4] [6] [13] [14]
NOTE 3 If the environmental correction K exceeds 4 dB, ISO 3743 , ISO 3747 , ISO 9614-1 or ISO 9614-2
2A
[5]
can be used for results of accuracy grade 2, or ISO 3746 can be used for results of accuracy grade 3.
NOTE 4 In some specific cases, the horizontal testing plane cannot be reflecting (e.g. lawnmowers, some types of
earth-moving machines). In such cases, a relevant noise test code describes in detail the nature of the plane on which the
noise source is mounted and indicates the possible consequences on the measurement uncertainty.
The environmental correction, K , is assumed to be zero for measurements made in hemi-anechoic rooms
which meet the requirements of ISO 3745.
For an outdoor space which consists of a hard, flat ground surface, such as asphalt or concrete, with no
sound-reflecting objects within a distance from the noise source equal to 10 times the greatest distance from
the geometric centre of the source to the lowest measurement points, it shall be assumed that the
environmental correction K is less than 0,5 dB and can be neglected.
4.3.2 Criterion for environmental correction
The environmental correction, K , shall first be determined without reference to frequency band data, using
2A
one of the procedures of Annex A. Then:
a) if K > 4 dB, this International Standard is not applicable (see 4.3.1);
2A
b) if K u 4 dB, measurements may be made in accordance with this International Standard, either in
2A
frequency bands or A-weighted, using measurement surfaces described in Annexes B, C and D — in
addition, for direct measurement of A-weighted sound pressure levels, the alternative microphone array
described in Annex F may be used.
Where it is decided to make measurements in frequency bands, the relevant environmental correction K shall
be determined in each band over the frequency range of interest in accordance with A.2 or A.3.4 and all
measurements to determine L or L of a noise source shall be made in frequency bands. L or L shall be
W J WA JA
calculated using the frequency-band levels, see Annex E.
5 Instrumentation
5.1 General
The instrumentation system, including the microphones, cables and windscreen, if used, shall meet the
requirements of IEC 61672-1:2002, class 1, and the filters shall meet the requirements of IEC 61260:1995,
class 1.
ISO 3744:2010(E)
5.2 Calibration
Before and after each series of measurements, a sound calibrator meeting the requirements of
IEC 60942:2003, class 1 shall be applied to each microphone to verify the calibration of the entire measuring
system at one or more frequencies within the frequency range of interest. Without any adjustment, the
difference between the readings made before and after each series of measurements shall be less than or
equal to 0,5 dB. If this value is exceeded, the results of the series of measurements shall be discarded.
The calibration of the sound calibrator, the compliance of the instrumentation system with the requirements of
IEC 61672-1, the compliance of the filter set with the requirements of IEC 61260, and, if used, the compliance
of the reference sound source with t
...