SIST EN ISO 3744:2009

Acoustics - Determination of sound power levels of noise sources using sound pressure - Engineering method in an essentially free field over a reflecting plane (ISO 3744:1994)

This lnternational Standard specifies a method for measuring the sound pressure levels on a rneasurement surface enveloping a noise source, under essentially free-field conditions near one or more reflecting planes, in order to calculate the sound power level produced by the noise source. It gives requirements for the test environment and instrumentation, as well as techniques for obtaining the surface sound pressure level from which the sound power level of the source is calculated, leading to results which have a grade 2 accuracy. It is important that specific noise test codes for various types of equipment be established and used in accordance with this lnternational Standard. For each type of equipment, such noise test codes will give detailed requirements on mounting, loading and operating conditions for the equipment under test as well as a selection of the measurement surface and the microphone array as specified in th~s lnternational Standard.

Akustik - Bestimmung der Schalleistungspegel von Geräuschquellen aus Schalldruckmessungen - Hüllflächenverfahren der Genauigkeitsklasse 2 für ein im wesentlichen freies Schallfeld über einer reflektierenden Ebene (ISO 3744:1994)

Acoustique - Détermination des niveaux de puissance acoustique émis par les sources de bruit à partir de la pression acoustique - Méthode d'expertise dans des conditions approchant celles du champ libre sur plan réfléchissant (ISO 3744:1994)

Enonce des définitions, des exigences, des méthodes d'essai et des valeurs nominales pour les dispositifs de couplage phase-terre capacitifs et blindage-terre inductifs intrusifs devant être utilisés sur des systèmes DLC moyenne tension.

Akustika - Ugotavljanje ravni zvočnih moči virov hrupa z merjenjem zvočnega tlaka - Inženirska metoda v pretežno prostem polju nad odbojno ravnino (ISO 3744:1994)

General Information

• Status: Withdrawn
• Public Enquiry End Date: 09-Jun-2009
• Publication Date: 12-Oct-2009
• Withdrawal Date: 25-Oct-2010
• ICS: 17.140.01 - Acoustic measurements and noise abatement in general
• Technical Committee: AKU - Acoustics
• Current Stage: 9900 - Withdrawal (Adopted Project)
• Start Date: 25-Oct-2010
• Due Date: 17-Nov-2010
• Completion Date: 26-Oct-2010
• Directive: 2006/42/EC - Directive 2006/42/EC of the European Parliament and of the Council of 17 May 2006 on machinery, and amending Directive 95/16/EC (recast)
• Directive: 89/392/EEC - Machinery - Safety of machinery: general essential health and safety requirements
• Directive: 98/37/EC - Machinery
• Mandate: M/BC/CEN/88/13 - Standardization request to CEN/CENELEC relating to machinery
• Ref Project: EN ISO 3744:2009 - Acoustics - Determination of sound power levels of noise sources using sound pressure - Engineering method in an essentially free field over a reflecting plane (ISO 3744:1994)

Relations

• Replaced By: SIST EN ISO 3744:2010 - 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)
• Effective Date: 01-Dec-2010
• Replaces: SIST EN ISO 3744:1997 - Acoustics - Determination of sound power levels of noise sources using sound pressure - Engineering method in an essentially free field over a reflecting plane (ISO 3744:1994)
• Effective Date: 01-Nov-2009

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 3744:2009
01-november-2009
1DGRPHãþD
SIST EN ISO 3744:1997
$NXVWLND8JRWDYOMDQMHUDYQL]YRþQLKPRþLYLURYKUXSD]PHUMHQMHP]YRþQHJD
WODND,QåHQLUVNDPHWRGDYSUHWHåQRSURVWHPSROMXQDGRGERMQRUDYQLQR,62

Acoustics - Determination of sound power levels of noise sources using sound pressure -
Engineering method in an essentially free field over a reflecting plane (ISO 3744:1994)
Akustik - Bestimmung der Schalleistungspegel von Geräuschquellen aus
Schalldruckmessungen - Hüllflächenverfahren der Genauigkeitsklasse 2 für ein im
wesentlichen freies Schallfeld über einer reflektierenden Ebene (ISO 3744:1994)
Acoustique - Détermination des niveaux de puissance acoustique émis par les sources
de bruit à partir de la pression acoustique - Méthode d'expertise dans des conditions
approchant celles du champ libre sur plan réfléchissant (ISO 3744:1994)
Ta slovenski standard je istoveten z: EN ISO 3744:2009
ICS:
17.140.01 $NXVWLþQDPHUMHQMDLQ Acoustic measurements and
EODåHQMHKUXSDQDVSORãQR noise abatement in general
SIST EN ISO 3744:2009 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 3744:2009

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SIST EN ISO 3744:2009
EUROPEAN STANDARD
EN ISO 3744
NORME EUROPÉENNE
EUROPÄISCHE NORM
July 2009
ICS 17.140.01 Supersedes EN ISO 3744:1995
English Version
Acoustics - Determination of sound power levels of noise
sources using sound pressure - Engineering method in an
essentially free field over a reflecting plane (ISO 3744:1994)
Acoustique - Détermination des niveaux de puissance Akustik - Bestimmung der Schalleistungspegel von
acoustique émis par les sources de bruit à partir de la Geräuschquellen aus Schalldruckmessungen -
pression acoustique - Méthode d'expertise dans des Hüllflächenverfahren der Genauigkeitsklasse 2 für ein im
conditions approchant celles du champ libre sur plan wesentlichen freies Schallfeld über einer reflektierenden
réfléchissant (ISO 3744:1994) Ebene (ISO 3744:1994)
This European Standard was approved by CEN on 13 July 2009.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2009 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 3744:2009: E
worldwide for CEN national Members.

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SIST EN ISO 3744:2009
EN ISO 3744:2009 (E)
Contents Page
Foreword .3
Annex ZA (informative) Relationship between this European Standard and the Essential
Requirements of EU Directive 98/37/EC .4
Annex ZB (informative) Relationship between this European Standard and the Essential
Requirements of EU Directive 2006/42/EC .5

2

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SIST EN ISO 3744:2009
EN ISO 3744:2009 (E)
Foreword
The text of ISO 3744:1994 has been prepared by Technical Committee ISO/TC 43 “Acoustics” of the
International Organization for Standardization (ISO) and has been taken over as EN ISO 3744:2009 by
Technical Committee CEN/TC 211 “Acoustics” the secretariat of which is held by DS.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by January 2010, and conflicting national standards shall be withdrawn at
the latest by January 2010.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 3744:1995.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association, and supports essential requirements of EC Directives.
For relationship with EC Directives, see informative Annexes ZA and ZB, which are integral parts of this
document.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 3744:1994 has been approved by CEN as a EN ISO 3744:2009 without any modification.
3

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SIST EN ISO 3744:2009
EN ISO 3744:2009 (E)
Annex ZA
(informative)

Relationship between this European Standard and the Essential
Requirements of EU Directive 98/37/EC
This European Standard has been prepared under a mandate given to CEN by the European Commission
and the European Free Trade Association to provide a means of conforming to Essential Requirements of the
New Approach Directive 98/37/EC, amended by 98/79/EC on machinery.
Once this standard is cited in the Official Journal of the European Communities under that Directive and has
been implemented as a national standard in at least one Member State, compliance with the normative
clauses of this standard confers, within the limits of the scope of this standard, a presumption of conformity
with the relevant Essential Requirements of that Directive and associated EFTA regulations.
WARNING - Other requirements and other EU Directives may be applicable to the product(s) falling within the
scope of this standard.
4

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SIST EN ISO 3744:2009
EN ISO 3744:2009 (E)
Annex ZB
(informative)

Relationship between this European Standard and the Essential
Requirements of EU Directive 2006/42/EC
This European Standard has been prepared under a mandate given to CEN by the European Commission
and the European Free Trade Association to provide a means of conforming to Essential Requirements of the
New Approach Directive 2006/42/EC on machinery.
Once this standard is cited in the Official Journal of the European Communities under that Directive and has
been implemented as a national standard in at least one Member State, compliance with the normative
clauses of this standard confers, within the limits of the scope of this standard, a presumption of conformity
with the relevant Essential Requirements of that Directive and associated EFTA regulations.
WARNING — Other requirements and other EU Directives may be applicable to the product(s) falling within
the scope of this standard.


5

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SIST EN ISO 3744:2009

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SIST EN ISO 3744:2009
INTERNATIONAL
STANDARD
3744
Second edition
1994-05-O 1
Acoustics - Determination of sound
power levels of noise sources using sound
pressure - Engineering method in an
essentially free field over a reflecting plane
Acoustique - Dgtermination des niveaux de puissance acoustique 6mis
par les sources de bruit P partir de la pression acoustique - M&hode
d’expertise dans des conditions approchant celles du champ libre sur plan
r6fkchissant
Reference number
IS0 3744:1994(E)

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SIST EN ISO 3744:2009
IS0 3744:1994(E)
Contents
Page
1
Scope .
2
Normative references .
....................................................................................... 3
Definitions
4
...............................................................
Acoustic environment
......................................................................... 5
Instrumentation
........................ 5
Installation and operation of source under test
................................... 7
Measurement of sound pressure levels
Calculation of surface sound pressure level and sound power
10
level .
12
Information to be recorded .
13
IO Information to be reported . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Annexes
. . . . . . . . 14
A Qualification procedures for the acoustic environment
18
B Microphone array on the hemispherical measurement surface
23
C Microphone array on the parallelepiped measurement surface
29
. . . . . . . . . . . . . . . . . . . .
D Guidelines for the detection of impulsive noise
. . . . . . 30
E Guidelines for the determination of the directivity index
31
F Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
0 IS0 1994
Ail rights reserved. 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 per-
mission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland
ii

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SIST EN ISO 3744:2009
IS0 3744:1994(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work
of preparing International Standards is normally carried out through IS0
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. IS0
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard IS0 3744 was prepared by Technical Committee
ISO/TC 43, Acoustics, Sub-Committee SC 1, Noise.
This second edition cancels and replaces the first edition
(IS0 3744: 1981), which has been technically revised.
Annexes A, B and C form an integral part of this International Standard.
Annexes D, E and F are for information only.

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SIST EN ISO 3744:2009
IS0 3744:1994(E)
Introduction
0.1 This International Standard is one of the IS0 3740 series, which
specifies various methods for determining the sound power levels of
machines, equipment and their sub-assemblies. When selecting one of
the methods of the IS0 3740 series, it is necessary to select the most
appropriate for the conditions and purposes of the noise test. General
guidelines to assist in the selection are provided in IS0 3740. The
IS0 3740 series gives only general principles regarding the operating and
mounting conditions of the machine or equipment under test. Reference
should be made to the noise test code for a specific type of machine or
equipment, if available, for specifications on mounting and operating con-
ditions.
0.2 This International Standard specifies a method for measuring the
sound pressure levels on a measurement surface enveloping the source,
and for calculating the sound power level produced by the source. The
enveloping surface method can be used for any of three grades of accu-
racy (see table O.l), and is used in this International Standard for grade 2
accuracy.
The use of this International Standard requires certain qualification criteria
to be fulfilled , as described in table 0.1. If the relevant qualification criteria
cannot be met, other basic standards with different environmental re-
quirements are suggested (tableO.l; see also IS0 3740 and IS0 9614).
Noise test codes for specific families of machines or equipment should
be based without any contradiction on the requirements of one or more
of the IS0 3740 series or IS0 9614.
Free-field conditions are usually not encountered in typical machine rooms
where sources are normally installed. If measurements are made in such
installations, corrections may be required to account for background noise
or undesired reflections.
The methods specified in this International Standard permit the determi-
nation of sound power level both as an A-weighted value and in frequency
bands.
The A-weighted value calculated fro m frequency band data may differ
from that determ ined f ram measu red A-weighted sound press ure levels.
0.3 In this International Standard, the computation of sound power level
from sound pressure level measurements is based on the premise that the
sound power output of the source is directly proportional to the mean-
square sound pressure averaged over time and space.

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SIST EN ISO 3744:2009
IS0 3744: 1994(E)
A. d.
I a1318 u.1 - uvervlew or InternatIonal StatWards tor determlnatlon
of sound power levels of noise sources using enveloping surface
methods over a reflecting plane and giving different grades of
accuracy
IS0 3746
IS0 3745 IS03744
Precision Engineering Survey
Parameter
method method method
Grade 1 Grade 2 Grade 3
Test environment
Hemi-anechoic Outdoors or Outdoors or
room indoors indoors
Criterion for suitability of test en- K2 < 0,5 dB K2 < 2 dB K2 < 7 dB
vironmentl)
Volume of sound source Preferably less No restriction; No restriction;
than 0,5 % of limited only by limited only by
test room vol- available test available test
ume environment environment
Character of noise
Any (broad-band, narrow-band, discrete-frequency,
steady, non-steady, impulsive)
Limitation for background noise’) ti 2 10 dB (if hL 2 6 dB (if hL>,3dB
possible, ex- possible, ex-
ceeding 15 dB) ceeding 15 dB)
K, < 0,4 dB K, < 1,3 dB K, <3dB
> 42)
Number of measurement points 2 10 a 92)
Instrumentation:
- Sound level meter at least a) type 1 as a) type 1 as a) type 2 as
complying with
specified specified specified
in IEC 651 in IEC 651 in IEC 651
- Integrating sound level meter b) type 1 as b) type 1 as b) type 2 as
at least complying with specified specified specified
in IEC 804 in IEC 804 in IEC 804
- Frequency band filter set at c) class 1 as c) class 1 as
least complying with specified specified
in IEC 225 in IEC 225
Precision of method for deter- aR, mining &A expressed as standard K2 < 5 dB)
deviation of reproducibility q G 4 dB (if
5dB < 7 dB)
If discrete
tones are pre-
dominant, the
value of oR is
1 dB greater.
1) The values of K, and K2 given shall be met in each frequency band within the fre-
quency range of interest for determining the sound power spectrum. For determining
A-weighted sound power levels, the same criteria apply to K,* and KzA.
2) Under given circumstances (see 7.2 to 7.4), it is permissible to use a reduced num-
ber of microphone positions.

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SIST EN ISO 3744:2009
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SIST EN ISO 3744:2009
INTERNATIONAL STANDARD IS0 3744: 1994(E)
Acoustics - Determination of sound power levels of
- Engineering
noise sources using sound pressure
method in an essentially free field over a reflecting
plane
This International Standard is applicable to noise
1 Scope
sources of any type and size (e.g. device, machine,
component, sub-assembly).
I .I General
NOTE 3 Measurements according to this International
Standard may be impracticable for very tall or very long
This International Standard specifies a method for sources such as chimneys, ducts, conveyors and multi-
source industrial plants.
measuring the sound pressure levels on a measure-
ment surface enveloping a noise source, under es-
sentially free-field conditions near one or more
1.3 Test environment
reflecting planes, in order to calculate the sound
power level produced by the noise source. It gives
The test environment that is applicable for measure-
requirements for the test environment and instru-
ments made in accordance with this International
mentation, as well as techniques for obtaining the
Standard is an essentially free field near one or more
surface sound pressure level from which the sound
reflecting planes (indoors or outdoors).
power level of the source is calculated, leading to re-
sults which have a grade 2 accuracy.
It is important that specific noise test codes for vari-
1.4 Measurement uncertainty
ous types of equipment be established and used in
accordance with this International Standard. For each
Determinations made in accordance with this Inter-
type of equipment, such noise test codes will give
national Standard result, with few exceptions, in
detailed requirements on mounting, loading and op-
standard deviations of reproducibility of the A-
erating conditions for the equipment under test as
weighted sound power level equal to or less than
well as a selection of the measurement surface and
I,5 dB (see table 1).
the microphone array as specified in this International
A single value of the sound power level of a noise
Standard.
source determined according to the procedures given
NOTE 1 The noise test code for a particular type of in this International Standard is likely to differ from the
equipment should give detailed information on the particular
true value by an amount within the range of the
surface that is selected, as the use of differently shaped
measurement uncertainty. The uncertainty in deter-
measurement surfaces may yield differing estimates of the
minations of the sound power level arises from sev-
sound power level of a source.
eral factors which affect the results, some associated
with environmental conditions in the measurement
laboratory and others with experimental techniques.
1.2 Types of noise and noise sowrces
If a particular noise source were to be transported to
each of a number of different laboratories, and if, at
The method specified in this International Standard is
each laboratory, the sound power level of that source
suitable for measurements of all types of noise.
were to be determined in accordance with this lnter-
national Standard, the results would show a scatter.
NOTE 2 A classification of different types of noise
The standard deviation of the measured levels could
(steady, non-steady, quasi-steady, impulsive, etc.) is given
in IS0 2204. be calculated (see examples in IS0 7574-4:1985, an-

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SIST EN ISO 3744:2009
IS0 3744: 1994(E)
location of microphone positions, sound source location, in-
nex B) and would vary with frequency. With few ex-
tegration times, and determination of environmental cor-
ceptions, these standard deviations would not exceed
rections, if any. The standard deviations are also affected
those listed in table 1. The values given in table 1 are
by errors associated with measurements taken in the near
standard deviations of reproducibility, Q, as defined
field of the source; such errors depend upon the nature of
in IS0 7574-l. The values of table 1 take into account
the sound source, but generally increase for smaller meas-
the cumulative effects of measurement uncertainty in
urement distances and lower frequencies (below 250 Hz).
applying the procedures of this International Standard,
but exclude variations in the sound power output
5 If several laboratories use similar facilities and instru-
caused by changes in operating conditions (e.g. rota-
mentation, the results of sound power determinations on a
tional speed, line voltage) or mounting conditions.
given source in those laboratories may be in better agree-
ment than would be implied by the standard deviations of
table 1.
The measurement uncertainty depends on the stan-
dard deviation of reproducibility tabulated in table 1
6 For a particular family of sound sources, of similar size
and on the degree of confidence that is desired. As
with similar sound power spectra and similar operating
examples, for a normal distribution of sound power
conditions, the standard deviations of reproducibility may
levels, there is 90 % confidence that the true value
be smaller than the values given in table 1. Hence, a noise
of the sound power level of a source lies within the
test code for a particular type of machinery or equipment
range + 1,645 OR of the measured value and a 95 %
making reference to this International Standard may state
confidence that it lies within the range + I,96 CR of
standard deviations smaller than those listed in table 1, if
the measured value. For further examples, reference substantiation is available from the results of suitable inter-
laboratory tests.
should be made to the IS0 7574 series and IS0 9296.
7 The standard deviations of reproducibility, as tabulated
in table 1, include the uncertainty associated with repeated
Table 1 - Estimated values of the standard
measurements on the same noise source under the same
deviations of reproducibility of sound power
conditions (for standard deviation of repeatability, see
levels determined in accordance with this IS0 7574-l). This uncertainty is usually much smaller than
the uncertainty associated with interlaboratory variability.
International Standard
However, if it is difficult to maintain stable operating or
Octave-band One-third-octave Standard
mounting conditions for a particular source, the standard
centre band centre deviation of
deviation of repeatability may not be small compared with
frequencies reproducibility
frequencies
the values given in table 1. In such cases, the fact that it
OR
was difficult to obtain repeatable sound power level data on
the source should be recorded and stated in the test report.
Hz Hz dB
8 The procedures of this International Standard and the
63 50 to 80 5 ‘1
standard deviations given in table 1 are applicable to meas-
125 100 to 160 3
urements on an individual machine. Characterization of the
250 200 to 315 2
sound power levels of batches of machines of the same
500 to 4 000 400 to 5 000 I,5
family or type involves the use of random sampling tech-
8 000 6300to10000 23
niques in which confidence intervals are specified, and the
results are expressed in terms of statistical upper limits. In
A-weighted I,5 2)
applying these techniques, the total standard deviation must
be known or estimated, including the standard deviation of
1) Normally for outdoor measurements; many rooms
production, as defined in IS0 7574-1, which is a measure
are not qualified for this frequency band.
of the variation in sound power output between individual
machines within the batch. Statistical methods for the
2) Applicable to a source which emits noise with a
characterization of batches of machines are described in
relatively “flat” spectrum in the frequency range
IS0 7574-4.
100 Hz to 10 000 Hz.
2 Normative references
NOTES
4 The standard deviations listed in table 1 are associated
The following standards contain provisions which,
with the test conditions and procedures defined in this
through reference in this text, constitute provisions
International Standard and not with the noise source itself.
of this International Standard. At the time of publi-
They arise in part from variations between measurement
cation, the editions indicated were valid. All standards
laboratories, changes in atmospheric conditions if outdoors,
are subject to revision, and parties to agreements
the geometry of the test room or outdoor environment, the
based on this International Standard are encouraged
acoustical properties of the reflecting plane, absorption at
to investigate the possibility of applying the most re-
the test room boundaries if indoors, background noise, and
cent editions of the standards indicated below.
the type and calibration of instrumentation. They are also
Members of IEC and IS0 maintain registers of cur-
due to variations in experimental techniques, including the
size and shape of the measurement surface, number and rently valid International Standards.

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SIST EN ISO 3744:2009
IS0 3744:1994(E)
IS0 354:1985, Acoustics - Measurement of sound 3.2 sound pressure level, Lp: Ten times the log-
absorption in a reverberation room. arithm to the base 10 of the ratio of the square of the
sound pressure to the square of the reference sound
IS0 2204:I 979, Acoustics - Guide to International pressure. Sound pressure levels are expressed in
decibels.
Standards on the measurement of airborne acoustical
noise and evaluation of its effects on human beings.
The frequency weighting or the width of the fre-
quency band used, and the time weighting (S, F or I,
IS0 3745:1977, Acoustics - Determination of sound
see IEC 651) shall be indicated. The reference sound
power levels of noise sources - Precision methods
pressure is 20 PPa (2 x low5 Pa).
for anechoic and semi-anechoic rooms.
NOTE 10 For example, the A-weighted sound pressure
IS0 374711987, Acoustics - Determination of sound
level with time weighting S is GAS.
power levels of noise sources - Survey method us-
ing a reference sound source.
3.2.1 time-averaged sound pressure level, Lpeq +
Sound pressure level of a continuous steady sound
IS0 4871 :1984, Acoustics - Noise labelling of ma-
that, within a measurement time interval T, has the
chinery and equipment.
same mean-square sound pressure as a sound under
consideration which varies with time:
IS0 6926:1990, Acoustics - Determination of sound
power levels of noise sources - Requirements for
the performance and calibration of reference sound
Lpeq,T= 10 Ig [+[,,,, dt] dB
sources.
IS0 7574-I :1985, Acoustics - Statistical methods for
= IO Ig [+[y di] dB . . .
(1)
determining and verifying stated noise emission val-
ues of machinery and equipment - Part 1: General
considerations and definitions.
Time-averaged sound pressure levels are expressed
in decibels and shall be measured with an instrument
IS0 7574-4:1985, Acoustics - Statistical methods for
which complies with the requirements of IEC 804.
determining and verifying stated noise emission val-
ues of machinery and equipment - Part 4: Methods
NOTES
for stated values for batches of machines.
11 Time-averaged sound pressure levels are usually A-
I EC 225: 1966, Octave, half-octave and third-octave
weighted and denoted by LpAeq,* which is usually abbrevi-
band filters intended for the analysis of sounds and
ated to LpA.
vibrations.
12 In general, the subscripts “eq” and “T” are omitted
since time-averaged sound pressure levels are necessarily
I EC 651: 1979, Sound level meters.
determined over a certain measurement time interval.
I EC 804: 1985, Integrating-averaging sound level me-
ters. 3.2.2 single-event sound pressure level, LP ,S:
Time-integrated sound pressure level of an isolated
I EC 942: 1988, Sound calibrators. single sound event of specified duration T (or speci-
fied measurement time 7’) normalized to To = I s. It is
expressed in decibels and is given by the following
formula:
r m r) 1
Lp.,s= IO lg[+-[Fdt]dB
3 Definitions
. . .
(2)
For the purposes of this International Standard, the
following definitions apply.
3.2.3 measurement time interval: A portion or a
3.1 sound pressure, p: A fluctuating pressure
multiple of an operational period or operational cycle
superimposed on the static pressure by the presence
for which the time-averaged sound pressure level is
of sound. It is expressed in pascals.
determined.
NOTE 9 The magnitude of the sound pressure can be
3.3 measurement surface: A hypothetical surface
expressed in several ways, such as instantaneous sound
of area S, enveloping the source, on which the meas-
pressure, maximum sound pressure, or as the square root
urement points are located. The me
...

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Akustik - Bestimmung der Schalleistungspegel von Geräuschquellen aus Schalldruckmessungen - Hüllflächenverfahren der Genauigkeitsklasse 2 für ein im wesentlichen freies Schallfeld über einer reflektierenden Ebene (ISO 3744:1994)Acoustique - Détermination des niveaux de puissance acoustique émis par les sources de bruit à partir de la pression acoustique - Méthode d'expertise dans des conditions approchant celles du champ libre sur plan réfléchissant (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 (ISO 3744:1994)17.140.01Acoustic measurements and noise abatement in generalICS:Ta slovenski standard je istoveten z:FprEN ISO 3744kSIST FprEN ISO 3744:2009en01-junij-2009kSIST FprEN ISO 3744:2009SLOVENSKI
STANDARD



kSIST FprEN ISO 3744:2009



EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMFINAL DRAFTFprEN ISO 3744March 2009ICS 17.140.01Will supersede EN ISO 3744:1995
English VersionAcoustics - Determination of sound power levels of noisesources using sound pressure - Engineering method in anessentially free field over a reflecting plane (ISO 3744:1994)Acoustique - Détermination des niveaux de puissanceacoustique émis par les sources de bruit à partir de lapression acoustique - Méthode d'expertise dans desconditions approchant celles du champ libre sur planréfléchissant (ISO 3744:1994)Akustik - Bestimmung der Schalleistungspegel vonGeräuschquellen aus Schalldruckmessungen -Hüllflächenverfahren der Genauigkeitsklasse 2 für ein imwesentlichen freies Schallfeld über einer reflektierendenEbene (ISO 3744:1994)This draft European Standard is submitted to CEN members for unique acceptance procedure. It has been drawn up by the TechnicalCommittee CEN/TC 211.If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations whichstipulate the conditions for giving this European Standard the status of a national standard without any alteration.This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other languagemade by translation under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has thesame status as the official versions.CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without notice andshall not be referred to as a European Standard.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre:
Avenue Marnix 17,
B-1000 Brussels© 2009 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. FprEN ISO 3744:2009: EkSIST FprEN ISO 3744:2009



FprEN ISO 3744:2009 (E) 2 Contents Page Foreword .3Annex ZA (informative)
Relationship between this European Standard and the Essential Requirements of EU Directive 98/37/EC .4Annex ZB (informative)
Relationship between this European Standard and the Essential Requirements of EU Directive 2006/42/EC .5 kSIST FprEN ISO 3744:2009



FprEN ISO 3744:2009 (E) 3 Foreword The text of ISO 3744:1994 has been prepared by Technical Committee ISO/TC 43 “Acoustics” of the International Organization for Standardization (ISO) and has been taken over as FprEN ISO 3744:2009 by Technical Committee CEN/TC 211 “Acoustics” the secretariat of which is held by DS. This document is currently submitted to the Unique Acceptance Procedure. This document will supersede EN ISO 3744:1995. This document has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association, and supports essential requirements of EC Directives. For relationship with EC Directives, see informative Annexes ZA and ZB, which are integral parts of this document. Endorsement notice The text of ISO 3744:1994 has been approved by CEN as a FprEN ISO 3744:2009 without any modification. kSIST FprEN ISO 3744:2009



FprEN ISO 3744:2009 (E) 4 Annex ZA (informative)
Relationship between this European Standard and the Essential Requirements of EU Directive 98/37/EC This European Standard has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association to provide a means of conforming to Essential Requirements of the New Approach Directive 98/37/EC, amended by 98/79/EC on machinery. Once this standard is cited in the Official Journal of the European Communities under that Directive and has been implemented as a national standard in at least one Member State, compliance with the normative clauses of this standard confers, within the limits of the scope of this standard, a presumption of conformity with the relevant Essential Requirements of that Directive and associated EFTA regulations. WARNING - Other requirements and other EU Directives may be applicable to the product(s) falling within the scope of this standard. kSIST FprEN ISO 3744:2009



FprEN ISO 3744:2009 (E) 5 Annex ZB (informative)
Relationship between this European Standard and the Essential Requirements of EU Directive 2006/42/EC This European Standard has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association to provide a means of conforming to Essential Requirements of the New Approach Directive 2006/42/EC on machinery. Once this standard is cited in the Official Journal of the European Communities under that Directive and has been implemented as a national standard in at least one Member State, compliance with the normative clauses of this standard confers, within the limits of the scope of this standard, a presumption of conformity with the relevant Essential Requirements of that Directive and associated EFTA regulations. WARNING — Other requirements and other EU Directives may be applicable to the product(s) falling within the scope of this standard.
kSIST FprEN ISO 3744:2009



kSIST FprEN ISO 3744:2009



INTERNATIONAL STANDARD 3744 Second edition 1994-05-O 1 Acoustics - Determination of sound power levels of noise sources using sound pressure - Engineering method in an essentially free field over a reflecting plane Acoustique - Dgtermination des niveaux de puissance acoustique 6mis par les sources de bruit P partir de la pression acoustique - M&hode d’expertise dans des conditions approchant celles du champ libre sur plan r6fkchissant Reference number IS0 3744:1994(E) kSIST FprEN ISO 3744:2009



IS0 3744:1994(E) Contents Page Scope . 1 Normative references . 2 Definitions . 3 Acoustic environment . 4 Instrumentation . 5 Installation and operation of source under test . 5 Measurement of sound pressure levels . 7 Calculation of surface sound pressure level and sound power level . 10 Information to be recorded . 12 IO Information to be reported Annexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 A Qualification procedures for the acoustic environment . . . . . . . . 14 B Microphone array on the hemispherical measurement surface 18 C Microphone array on the parallelepiped measurement surface 23 D Guidelines for the detection of impulsive noise . . . . . . . . . . . . . . . . . . . . 29 E Guidelines for the determination of the directivity index . . . . . . 30 F Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 0 IS0 1994 Ail rights reserved. 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 per- mission in writing from the publisher. International Organization for Standardization Case Postale 56 l CH-1211 Geneve 20 l Switzerland Printed in Switzerland ii kSIST FprEN ISO 3744:2009



IS0 3744:1994(E) Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 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. IS0 collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard IS0 3744 was prepared by Technical Committee ISO/TC 43, Acoustics, Sub-Committee SC 1, Noise. This second edition cancels and replaces the first edition (IS0 3744: 1981), which has been technically revised. Annexes A, B and C form an integral part of this International Standard. Annexes D, E and F are for information only. kSIST FprEN ISO 3744:2009



IS0 3744:1994(E) Introduction 0.1 This International Standard is one of the IS0 3740 series, which specifies various methods for determining the sound power levels of machines, equipment and their sub-assemblies. When selecting one of the methods of the IS0 3740 series, it is necessary to select the most appropriate for the conditions and purposes of the noise test. General guidelines to assist in the selection are provided in IS0 3740. The IS0 3740 series gives only general principles regarding the operating and mounting conditions of the machine or equipment under test. Reference should be made to the noise test code for a specific type of machine or equipment, if available, for specifications on mounting and operating con- ditions. 0.2 This International Standard specifies a method for measuring the sound pressure levels on a measurement surface enveloping the source, and for calculating the sound power level produced by the source. The enveloping surface method can be used for any of three grades of accu- racy (see table O.l), and is used in this International Standard for grade 2 accuracy. The use of this International Standard requires certain qualification criteria to be fulfilled , as described in table 0.1. If the relevant qualification criteria cannot be met, other basic standards with different environmental re- quirements are suggested (tableO.l; see also IS0 3740 and IS0 9614). Noise test codes for specific families of machines or equipment should be based without any contradiction on the requirements of one or more of the IS0 3740 series or IS0 9614. Free-field conditions are usually not encountered in typical machine rooms where sources are normally installed. If measurements are made in such installations, corrections may be required to account for background noise or undesired reflections. The methods specified in this International Standard permit the determi- nation of sound power level both as an A-weighted value and in frequency bands. The A-weighted value from that determ ined f calculated ram measu fro m frequency band data may differ red A-weighted sound press ure levels. 0.3 In this International Standard, the computation of sound power level from sound pressure level measurements is based on the premise that the sound power output of the source is directly proportional to the mean- square sound pressure averaged over time and space. kSIST FprEN ISO 3744:2009



IS0 3744: 1994(E) A. d. I a1318 u.1 - uvervlew or InternatIonal StatWards tor determlnatlon of sound power levels of noise sources using enveloping surface methods over a reflecting plane and giving different grades of accuracy IS0 3745 IS03744 IS0 3746 Parameter Precision Engineering Survey method method method Grade 1 Grade 2 Grade 3 Test environment Hemi-anechoic Outdoors or Outdoors or room indoors indoors Criterion for suitability of test en- K2 < 0,5 dB K2 < 2 dB K2 < 7 dB vironmentl) Volume of sound source Preferably less No restriction; than 0,5 % of limited only by test room vol- available test ume environment No restriction; limited only by available test environment Character of noise Any (broad-band, narrow-band, discrete-frequency, steady, non-steady, impulsive) Limitation for background noise’) ti 2 10 dB (if hL 2 6 dB (if hL>,3dB possible, ex- possible, ex- ceeding 15 dB) ceeding 15 dB) K, < 0,4 dB K, < 1,3 dB K, <3dB Number of measurement points 2 10 a 92) > 42) Instrumentation: - Sound level meter at least a) type 1 as a) type 1 as a) type 2 as complying with specified specified specified in IEC 651 in IEC 651 in IEC 651 - Integrating sound level meter b) type 1 as b) type 1 as b) type 2 as at least complying with specified specified specified in IEC 804 in IEC 804 in IEC 804 - Frequency band filter set at c) class 1 as c) class 1 as least complying with specified specified in IEC 225 in IEC 225 Precision of method for deter- aR,


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INTERNATIONAL STANDARD IS0 3744: 1994(E) Acoustics - Determination of sound power levels of noise sources using sound pressure - Engineering method in an essentially free field over a reflecting plane 1 Scope I .I General This International Standard specifies a method for measuring the sound pressure levels on a measure- ment surface enveloping a noise source, under es- sentially free-field conditions near one or more reflecting planes, in order to calculate the sound power level produced by the noise source. It gives requirements for the test environment and instru- mentation, as well as techniques for obtaining the surface sound pressure level from which the sound power level of the source is calculated, leading to re- sults which have a grade 2 accuracy. It is important that specific noise test codes for vari- ous types of equipment be established and used in accordance with this International Standard. For each type of equipment, such noise test codes will give detailed requirements on mounting, loading and op- erating conditions for the equipment under test as well as a selection of the measurement surface and the microphone array as specified in this International Standard. NOTE 1 The noise test code for a particular type of equipment should give detailed information on the particular surface that is selected, as the use of differently shaped measurement surfaces may yield differing estimates of the sound power level of a source. 1.2 Types of noise and noise sowrces The method specified in this International Standard is suitable for measurements of all types of noise. NOTE 2 A classification of different types of noise (steady, non-steady, quasi-steady, impulsive, etc.) is given in IS0 2204. This International Standard is applicable to noise sources of any type and size (e.g. device, machine, component, sub-assembly). NOTE 3 Measurements according to this International Standard may be impracticable for very tall or very long sources such as chimneys, ducts, conveyors and multi- source industrial plants. 1.3 Test environment The test environment that is applicable for measure- ments made in accordance with this International Standard is an essentially free field near one or more reflecting planes (indoors or outdoors). 1.4 Measurement uncertainty Determinations made in accordance with this Inter- national Standard result, with few exceptions, in standard deviations of reproducibility of the A- weighted sound power level equal to or less than I,5 dB (see table 1). A single value of the sound power level of a noise source determined according to the procedures given in this International Standard is likely to differ from the true value by an amount within the range of the measurement uncertainty. The uncertainty in deter- minations of the sound power level arises from sev- eral factors which affect the results, some associated with environmental conditions in the measurement laboratory and others with experimental techniques. If a particular noise source were to be transported to each of a number of different laboratories, and if, at each laboratory, the sound power level of that source were to be determined in accordance with this lnter- national Standard, the results would show a scatter. The standard deviation of the measured levels could be calculated (see examples in IS0 7574-4:1985, an- kSIST FprEN ISO 3744:2009



IS0 3744: 1994(E) nex B) and would vary with frequency. With few ex- ceptions, these standard deviations would not exceed those listed in table 1. The values given in table 1 are standard deviations of reproducibility, Q, as defined in IS0 7574-l. The values of table 1 take into account the cumulative effects of measurement uncertainty in applying the procedures of this International Standard, but exclude variations in the sound power output caused by changes in operating conditions (e.g. rota- tional speed, line voltage) or mounting conditions. The measurement uncertainty depends on the stan- dard deviation of reproducibility tabulated in table 1 and on the degree of confidence that is desired. As examples, for a normal distribution of sound power levels, there is 90 % confidence that the true value of the sound power level of a source lies within the range + 1,645 OR of the measured value and a 95 % confidence that it lies within the range + I,96 CR of the measured value. For further examples, reference should be made to the IS0 7574 series and IS0 9296. Table 1 - Estimated values of the standard deviations of reproducibility of sound power levels determined in accordance with this International Standard Octave-band One-third-octave Standard centre band centre deviation of frequencies frequencies reproducibility OR Hz Hz dB 63 50 to 80 5 ‘1 125 100 to 160 3 250 200 to 315 2 500 to 4 000 400 to 5 000 I,5 8 000 6300to10000 23 A-weighted I,5 2) 1) Normally for outdoor measurements; many rooms are not qualified for this frequency band. 2) Applicable to a source which emits noise with a relatively “flat” spectrum in the frequency range 100 Hz to 10 000 Hz. NOTES 4 The standard deviations listed in table 1 are associated with the test conditions and procedures defined in this International Standard and not with the noise source itself. They arise in part from variations between measurement laboratories, changes in atmospheric conditions if outdoors, the geometry of the test room or outdoor environment, the acoustical properties of the reflecting plane, absorption at the test room boundaries if indoors, background noise, and the type and calibration of instrumentation. They are also due to variations in experimental techniques, including the size and shape of the measurement surface, number and location of microphone positions, sound source location, in- tegration times, and determination of environmental cor- rections, if any. The standard deviations are also affected by errors associated with measurements taken in the near field of the source; such errors depend upon the nature of the sound source, but generally increase for smaller meas- urement distances and lower frequencies (below 250 Hz). 5 If several laboratories use similar facilities and instru- mentation, the results of sound power determinations on a given source in those laboratories may be in better agree- ment than would be implied by the standard deviations of table 1. 6 For a particular family of sound sources, of similar size with similar sound power spectra and similar operating conditions, the standard deviations of reproducibility may be smaller than the values given in table 1. Hence, a noise test code for a particular type of machinery or equipment making reference to this International Standard may state standard deviations smaller than those listed in table 1, if substantiation is available from the results of suitable inter- laboratory tests. 7 The standard deviations of reproducibility, as tabulated in table 1, include the uncertainty associated with repeated measurements on the same noise source under the same conditions (for standard deviation of repeatability, see IS0 7574-l). This uncertainty is usually much smaller than the uncertainty associated with interlaboratory variability. However, if it is difficult to maintain stable operating or mounting conditions for a particular source, the standard deviation of repeatability may not be small compared with the values given in table 1. In such cases, the fact that it was difficult to obtain repeatable sound power level data on the source should be recorded and stated in the test report. 8 The procedures of this International Standard and the standard deviations given in table 1 are applicable to meas- urements on an individual machine. Characterization of the sound power levels of batches of machines of the same family or type involves the use of random sampling tech- niques in which confidence intervals are specified, and the results are expressed in terms of statistical upper limits. In applying these techniques, the total standard deviation must be known or estimated, including the standard deviation of production, as defined in IS0 7574-1, which is a measure of the variation in sound power output between individual machines within the batch. Statistical methods for the characterization of batches of machines are described in IS0 7574-4. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publi- cation, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most re- cent editions of the standards indicated below. Members of IEC and IS0 maintain registers of cur- rently valid International Standards. kSIST FprEN ISO 3744:2009



IS0 3744:1994(E) IS0 354:1985, Acoustics - Measurement of sound absorption in a reverberation room. IS0 2204:I 979, Acoustics - Guide to International Standards on the measurement of airborne acoustical noise and evaluation of its effects on human beings. IS0 3745:1977, Acoustics - Determination of sound power levels of noise sources - Precision methods for anechoic and semi-anechoic rooms. IS0 374711987, Acoustics - Determination of sound power levels of noise sources - Survey method us- ing a reference sound source. IS0 4871 :1984, Acoustics - Noise labelling of ma- chinery and equipment. IS0 6926:1990, Acoustics - Determination of sound power levels of noise sources - Requirements for the performance and calibration of reference sound sources. IS0 7574-I :1985, Acoustics - Statistical methods for determining and verifying stated noise emission val- ues of machinery and equipment - Part 1: General considerations and definitions. IS0 7574-4:1985, Acoustics - Statistical methods for determining and verifying stated noise emission val- ues of machinery and equipment - Part 4: Methods for stated values for batches of machines. I EC 225: 1966, Octave, half-octave and third-octave band filters intended for the analysis of sounds and vibrations. I EC 651: 1979, Sound level meters. I EC 804: 1985, Integrating-averaging sound level me- ters. I EC 942: 1988, Sound calibrators. 3 Definitions For the purposes of this International Standard, the following definitions apply. 3.1 sound pressure, p: A fluctuating pressure superimposed on the static pressure by the presence of sound. It is expressed in pascals. NOTE 9 The magnitude of the sound pressure can be expressed in several ways, such as instantaneous sound pressure, maximum sound pressure, or as the square root of the mean-square sound pressure over designated time and space (i.e. over the measurement surface). 3.2 sound pressure level, Lp: Ten times the log- arithm to the base 10 of the ratio of the square of the sound pressure to the square of the reference sound pressure. Sound pressure levels are expressed in decibels. The frequency weighting or the width of the fre- quency band used, and the time weighting (S, F or I, see IEC 651) shall be indicated. The reference sound pressure is 20 PPa (2 x low5 Pa). NOTE 10 For example, the A-weighted sound pressure level with time weighting S is GAS. 3.2.1 time-averaged sound pressure level, Lpeq + 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: Lpeq,T= 10 Ig [+[,,,, dt] dB = IO Ig [+[y di] dB . . . (1) Time-averaged sound pressure levels are expressed in decibels and shall be measured with an instrument which complies with the requirements of IEC 804. NOTES 11 Time-averaged sound pressure levels are usually A- weighted and denoted by LpAeq,* which is usually abbrevi- ated to LpA. 12 In general, the subscripts “eq” and “T” are omitted since time-averaged sound pressure levels are necessarily determined over a certain measurement time interval. 3.2.2 single-event sound pressure level, LP ,S: Time-integrated sound pressure level of an isolated single sound event of specified duration T (or speci- fied measurement time 7’) normalized to To = I s. It is expressed in decibels and is given by the following formula: r m r) 1 Lp.,s= IO lg[+-[Fdt]dB . . . (2) 3.2.3 measurement time interval: A portion or a multiple of an operational period or operational cycle for which the time-averaged sound pressure level is determined. 3.3 measurement surface: A hypothetical surface of area S, enveloping the source, on which the meas- urement points are located. The measurement sur- face terminates on one or more reflecting planes. kSIST FprEN ISO 3744:2009



IS0 3744:1994(E) 3.4 surface sound pressure level, L&: The energy- average of the time-averaged sound pressure levels at all the microphone positions on the measurement surface, with the background noise correction K, (3.15) and the environmental correction K2 (3.16) ap- plied. It is expressed in decibels. 3.5 sound power, W: The rate per unit time at which airborne sound energy is radiated by a source. It is expressed in watts. 3.6 sound power level,.&: Ten times the logarithm to the base 10 of the ratio of the sound power radi- ated by the sound source under test to the reference sound power. It is expressed in decibels. The frequency weighting or the width of the fre- quency band used shall be indicated. The reference sound power is 1 pW (lo-l2 W). NOTE 13 For example, the A-weighted sound power level is &A. 3.7 free field: A sound field in a homogeneous, isotropic medium free of boundaries. In practice, it is a field in which reflections at the boundaries are neg- ligible over the frequency range of interest. 3.8 free field over a reflecting plane: A sound field in a homogeneous, isotropic medium in the half-space above an infinite, rigid plane surface on which the source is located. 3.9 frequency range of interest: For general pur- poses, the frequency range of interest includes the octave bands with centre frequencies from 125 Hz to 8 000 Hz. NOTE 14 For special purposes, it is permissible to extend or reduce the frequency range of interest at either end, provided the test environment and instrument accuracy are satisfactory for use over the extended or reduced frequency range. For sources which radiate predominantly high (or low) frequency sound, it is permissible to extend or reduce the frequency range of interest, in order to optimize the test facility and procedures. 3.10 reference box: A hypothetical surface which is the smallest rectangular parallelepiped that just en- closes the source and terminates on the reflecting plane or planes. 3.11 characteristic source dimension, 4: Half the length of the diagonal of the box consisting of the reference box and its images in adjoining re
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