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)

ISO 3744:2010 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 frequency A-weighting applied, is calculated using those measurements.
The methods specified in ISO 3744:2010 are suitable for all types of noise (steady, non-steady, fluctuating, isolated bursts of sound energy, etc.) defined in ISO 12001.
ISO 3744:2010 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.
The test environments that are applicable for measurements made in accordance with ISO 3744:2010 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.
Information is given on the uncertainty of the sound power levels and sound energy levels determined in accordance with ISO 3744:2010, 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).

Akustik - Bestimmung der Schallleistungs- und Schallenergiepegel von Geräuschquellen aus Schalldruckmessungen - Hüllflächenverfahren der Genauigkeitsklasse 2 für ein im Wesentlichen freies Schallfeld über einer reflektierenden Ebene (ISO 3744:2010)

1.1 Allgemeines
Diese Internationale Norm legt Verfahren für die Bestimmung des Schallleistungs- oder Schallenergiepegels
einer Geräuschquelle aus Schalldruckpegeln fest, die auf einer Fläche gemessen werden, die die
Geräuschquelle (eine Maschine oder ein Gerät) umschließt (Hüllfläche), wobei sich die Geräuschquelle in
einer Umgebung befindet, die angenähert einem akustischen Freifeld in der Nähe einer oder mehrerer
reflektierender Ebenen entspricht. Der von der Geräuschquelle erzeugte Schallleistungspegel (oder Schallenergiepegel
bei Impulsen oder anderen Geräuschen kurzer Dauer) in Frequenzbändern oder mit
A-Bewertung wird aus den Ergebnissen dieser Messungen berechnet.
ANMERKUNG Unterschiedliche Messflächenformen können zu unterschiedlichen Werten des Schallleistungspegels der
betrachteten Geräuschquelle führen. Daher sind in einer

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 (ISO 3744:2010)

L'ISO 3744:2010 spécifie des méthodes de détermination du niveau de puissance acoustique ou du niveau d'énergie acoustique émis par une source de bruit à partir des niveaux de pression acoustique mesurés sur une surface entourant la source de bruit (machine ou équipement), dans des conditions approchant celles du champ acoustique libre au voisinage d'un ou de plusieurs plans réfléchissants. Le niveau de puissance acoustique (ou, dans le cas d'impulsions sonores ou d'émissions sonores transitoires, le niveau d'énergie acoustique) produit par la source de bruit, par bandes de fréquences ou avec la pondération A appliquée, est calculé en utilisant ces mesures.
Les méthodes spécifiées dans l'ISO 3744:2010 sont applicables à tous les types de bruit (stable, non stable, fluctuant, impulsions acoustiques isolées, etc.) définis dans l'ISO 12001.
L'ISO 3744:2010 s'applique à tous les types de sources de bruit, quelles que soient leurs dimensions (par exemple installation, dispositif, machine, composant, sous-ensemble fixe ou se déplaçant lentement), sous réserve de pouvoir satisfaire les conditions de mesurage.
Les environnements d'essai qui sont applicables aux mesurages réalisés conformément à l'ISO 3744:2010 peuvent être en salle ou en plein air, comprendre un ou plusieurs plans acoustiques réfléchissants sur lesquels ou à proximité desquels est montée la source de bruit en essai. L'environnement idéal est un espace complètement libre, dépourvu de surfaces limites ou réfléchissantes autres que le ou les plans réfléchissants (tels que ceux d'une salle semi-anéchoïque qualifiée), mais des méthodes sont fournies pour appliquer des corrections (dans des limites spécifiées) lorsque ces environnements ne correspondent pas à ces conditions idéales.
Des informations sont données sur l'incertitude associée aux niveaux de puissance acoustique et aux niveaux d'énergie acoustique déterminés conformément à l'ISO 3744:2010 pour des mesurages effectués dans des bandes de fréquences limitées et avec la pondération fréquentielle A. L'incertitude est conforme à celle de la classe de précision 2 (classe expertise) définie dans l'ISO 12001:1996.

Akustika - Ugotavljanje ravni zvočnih moči virov hrupa z merjenjem zvočnega tlaka - Inženirska metoda v pretežno prostem polju nad odbojno ravnino (ISO 3744:2010)

Ta mednarodni standard določa metode ugotavljanja ravni moči zvoka ali ravni energije zvoka iz virov hrupa iz ravni zvočnega tlaka, merjenih na površju, ki obdaja vir hrupa (stroji ali oprema), v okolju, ki se približuje akustičnemu prostemu polju v bližini ene ali več odbojnih ravnin. Raven moči zvoka (ali v primeru prodorov hrupa ali prehodnih emisij hrupa raven zvočne energije), ki jo proizvede vir hrupa v frekvenčnih pasovih ali z uporabljenim A-uteženjem, je izračunana z uporabo teh merjenj.

General Information

Status
Published
Publication Date
30-Sep-2010
Technical Committee
Drafting Committee
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
01-Oct-2010
Completion Date
01-Oct-2010

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SLOVENSKI STANDARD
SIST EN ISO 3744:2010
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
SIST EN ISO 3744:2010 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN ISO 3744:2010
---------------------- Page: 2 ----------------------
SIST EN ISO 3744:2010
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.
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SIST EN ISO 3744:2010
EN ISO 3744:2010 (E)
Contents Page

Foreword ..............................................................................................................................................................3

Annex ZA .............................................................................................................................................................4

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SIST EN ISO 3744:2010
EN ISO 3744:2010 (E)
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.

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SIST EN ISO 3744:2010
EN ISO 3744:2010 (E)
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.
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SIST EN ISO 3744:2010
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
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SIST EN ISO 3744:2010
ISO 3744:2010(E)
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ii © ISO 2010 – All rights reserved
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SIST EN ISO 3744:2010
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 2010 – All rights reserved iii
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SIST EN ISO 3744:2010
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
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SIST EN ISO 3744:2010
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.
© ISO 2010 – All rights reserved v
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SIST EN ISO 3744:2010
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SIST EN ISO 3744:2010
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 2010 – All rights reserved 1
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SIST EN ISO 3744:2010
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
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

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
L = 10 lg dB (1)
where the reference value, p , is 20 µPa
[20]
[ISO/TR 25417:2007 , 2.2]
2 © ISO 2010 – All rights reserved
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SIST EN ISO 3744:2010
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.

[21]

NOTE 2 This definition is technically in accordance with ISO 80000-8:2007 , 8-22.

3.3
time-averaged sound pressure level
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
⎡⎤2
pt()dt
⎢⎥1
L = 10 lg dB (2)
pT,
⎢⎥2
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 .
[20]
NOTE 3 Adapted from ISO/TR 25417:2007 , 2.3.
3.4
single event time-integrated sound pressure level

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
pt()dt
⎢⎥1
L = 10 lg dB (3)
2 −10 2
where the reference value, E , is (20 µPa) s = 4 × 10 Pa s
NOTE 1 This quantity can be obtained by L +10 lg dB , where T = 1 s.
pT,

NOTE 2 When used to measure sound immission, this quantity is usually called “sound exposure level”

[20]
(see ISO/TR 25417:2007 ).
© ISO 2010 – All rights reserved 3
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SIST EN ISO 3744:2010
ISO 3744:2010(E)
3.5
measurement time interval

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

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
distance from the reference box to a parallelepiped measurement surface
NOTE Measurement distance is expressed in metres.
3.13
measurement radius

radius of a hemispherical, half-hemispherical or quarter-hemispherical measurement surface

NOTE Measurement radius is expressed in metres.
4 © ISO 2010 – All rights reserved
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SIST EN ISO 3744:2010
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

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

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

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

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 2010 – All rights reserved 5
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SIST EN ISO 3744:2010
ISO 3744:2010(E)
3.20
sound power

through a surface, product of the sound pressure, p, and the component of the particle velocity, u , at a point

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

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
L = 10 lg dB (4)
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 subscript
...

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