Power transformers - Part 10: Determination of sound levels

IEC 60076-10:2016 defines sound pressure and sound intensity measurement methods from which sound power levels of transformers, reactors and their associated cooling devices are determined. The methods are applicable to transformers, reactors and their cooling devices - either fitted to or separate from the transformer - as covered by the IEC 60076 and IEC 61378 series. This standard is primarily intended to apply to measurements made at the factory. Conditions on-site can be very different because of the proximity of objects, including other transformers. Nevertheless, this standard is applied to the extent possible for on site measurements. This edition includes the following significant technical changes with respect to the previous edition: - additional useful definitions introduced; - definition of distribution type transformers introduced for the purpose this standard; - new clause for sound level measurement specification introduced; - requirement for 1/3 octave band measurements introduced for transformers other than distribution type transformers; - standard measurement distance changed from 0,3 m to 1 m for transformers other than distribution type transformers; - height of measurement surface is now clearly defined to count from the reflecting plane; - measurement surface formula unified; - correction criteria for intensity method introduced; - rules for sound measurements on dry-type reactors introduced; - figures revised; - new informative test report templates introduced (Annex B); - IEC 60076-10-1 (application guide) revised in parallel providing worthwhile information for the use of this standard.

Leistungstransformatoren - Teil 10: Bestimmung der Geräuschpegel

Transformateurs de puissance - Partie 10: Détermination des niveaux de bruit

L'IEC 60076-10:2016 définit les méthodes de mesure de la pression acoustique et de l'intensité acoustique par lesquelles sont déterminés les niveaux de puissance acoustique des transformateurs, des bobines d'inductance et de leurs dispositifs de refroidissement associés. Les méthodes sont applicables aux transformateurs, aux bobines d'inductance et à leurs dispositifs de refroidissement - qu'ils soient installés sur le transformateur ou en soient séparés - comme décrit dans les séries IEC 60076 et IEC 61378. La présente norme est principalement destinée aux mesures effectuées en usine. Les conditions sur le site peuvent être très différentes, à cause de la proximité d'autres objets, en particulier d'autres transformateurs. Néanmoins, la présente norme est appliquée dans la mesure du possible aux mesures sur le site. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente: - introduction de définitions utiles supplémentaires; - introduction d'une définition des transformateurs de distribution pour les besoins de la présente norme; - introduction d'un nouvel article relatif à la spécification des mesures du niveau de bruit; - introduction d'une exigence relative aux mesures de la bande de 1/3 d'octave concernant les transformateurs autres que les transformateurs de distribution; - modification de la distance de mesure normalisée qui passe de 0,3 m à 1 m pour les transformateurs autres que les transformateurs de distribution; - la hauteur de la surface de mesure est désormais clairement définie à partir du plan réfléchissant; - unification de la formule relative à la surface de mesure; - introduction de critères de correction concernant la méthode d'intensité; - introduction de règles relatives aux mesures du son sur des bobines d'inductance de type sec; - révision des figures; - introduction de nouveaux modèles de rapport d'essai informatifs (Annexe B); - révision de l'IEC 60076-10-1 (guide d'application) en parallèle et ajout d'informations utiles relatives à l'utilisation de la présente norme.

Močnostni transformatorji - 10. del: Opredelitev zvočnih jakosti

Ta del standarda IEC 60076 določa metode merjenja zvočnega tlaka in jakosti, na podlagi katerih se določijo ravni zvočne moči transformatorjev, reaktorjev in njihovih hladilnih naprav.
OPOMBA: za namene tega standarda izraz »transformator« pogosto pomeni »transformator ali reaktor«.
Metode se uporabljajo za transformatorje, reaktorje in njihove hladilne naprave (vgrajene v transformator ali ločene), kot določata skupini standardov IEC 60076 in IEC 61378.
Ta standard je namenjen zlasti uporabi za merjenja v tovarni. Pogoji na mestu uporabe se lahko zelo razlikujejo zaradi bližine objektov, vključno z drugimi transformatorji. Kljub temu se standard v največji možni meri uporablja za merjenja na mestu uporabe.

General Information

Status
Published
Publication Date
10-Nov-2016
Technical Committee
Drafting Committee
Current Stage
6060 - Document made available
Due Date
28-Jun-2016

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SLOVENSKI STANDARD
SIST EN 60076-10:2017
01-januar-2017
1DGRPHãþD
SIST EN 60076-10:2002
0RþQRVWQLWUDQVIRUPDWRUMLGHO2SUHGHOLWHY]YRþQLKMDNRVWL
Power transformers - Part 10: Determination of sound levels
Leistungstransformatoren - Teil 10: Bestimmung der Geräuschpegel
Transformateurs de puissance - Partie 10: Détermination des niveaux de bruit
Ta slovenski standard je istoveten z: EN 60076-10:2016
ICS:
17.140.20 Emisija hrupa naprav in Noise emitted by machines
opreme and equipment
29.180 Transformatorji. Dušilke Transformers. Reactors
SIST EN 60076-10:2017 en

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

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SIST EN 60076-10:2017
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SIST EN 60076-10:2017
EUROPEAN STANDARD EN 60076-10
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2016
ICS 29.180 Supersedes EN 60076-10:2001
English Version
Power transformers -
Part 10: Determination of sound levels
(IEC 60076-10:2016)
Transformateurs de puissance - Leistungstransformatoren -

Partie 10: Détermination des niveaux de bruit Teil 10: Bestimmung der Geräuschpegel

(IEC 60076-10:2016) (IEC 60076-10:2016)

This European Standard was approved by CENELEC on 2016-10-17. CENELEC members are bound to comply with the CEN/CENELEC

Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC

Management Centre or to any CENELEC 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 CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the

same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,

Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,

Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2016 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Ref. No. EN 60076-10:2016 E
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SIST EN 60076-10:2017
EN 60076-10:2016
European foreword

This document (EN 60076-10:2016) consists of the text of IEC 60076-10:2016 prepared by IEC/TC 14

"Power transformers".
The following dates are fixed:
(dop) 2017-10-17
• latest date by which the document has to be
implemented
at national level by publication of an identical
national standard or by endorsement
• latest date by which the national standards conflicting (dow) 2019-10-17
with the document have to be withdrawn
This document supersedes EN 60076-10:2001.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such

patent rights.
Endorsement notice

The text of the International Standard IEC 60076-10:2016 was approved by CENELEC as a European

Standard without any modification.
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SIST EN 60076-10:2017
EN 60076-10:2016
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

references, the latest edition of the referenced document (including any amendments) applies.

NOTE 1 When an International Publication has been modified by common modifications, indicated by (mod), the relevant

EN/HD applies.

NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available here:

www.cenelec.eu
Publication Year Title EN/HD Year
IEC 60076-1 2011 Power transformers - EN 60076-1 2011
Part 1: General
IEC 60076-8 1997 Power transformers - - -
Part 8: Application guide
IEC 61043 1993 Electroacoustics - Instruments for the EN 61043 1994
measurement of sound intensity -
Measurement with pairs of pressure
sensing microphones
IEC 61672-1 - Electroacoustics - Sound level meters - EN 61672-1 -
Part 1: Specifications
IEC 61672-2 - Electroacoustics - Sound level meters - EN 61672-2 -
Part 2: Pattern evaluation tests
ISO 3382-2 2008 Acoustics - Measurement of room EN ISO 3382-2 2008
acoustic parameters -
Part-2: Reverberation time in ordinary
rooms
ISO 3746 2010 Acoustics - Determination of sound power EN ISO 3746 2010
levels and sound energy levels of noise
sources using sound pressure - Survey
method using an enveloping measurement
surface over a reflecting plane
ISO 9614-1 1993 Acoustics - Determination of sound power EN ISO 9614-1 2009
levels of noise sources using sound
intensity -
Part 1: Measurement at discrete points
ISO 9614-2 1996 Acoustics - Determination of sound power EN ISO 9614-2 1996
levels of noise sources using sound
intensity -
Part-2: Measurement by scanning
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SIST EN 60076-10:2017
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SIST EN 60076-10:2017
IEC 60076-10
Edition 2.0 2016-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Power transformers –
Part 10: Determination of sound levels
Transformateurs de puissance –
Partie 10: Détermination des niveaux de bruit
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.180 ISBN 978-2-8322-3252-1

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
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SIST EN 60076-10:2017
– 2 – IEC 60076-10:2016  IEC 2016
CONTENTS

FOREWORD ......................................................................................................................... 4

INTRODUCTION ................................................................................................................... 6

1 Scope ............................................................................................................................ 8

2 Normative references..................................................................................................... 8

3 Terms and definitions .................................................................................................... 9

4 Sound power for different loading conditions ................................................................ 11

4.1 General ............................................................................................................... 11

4.2 Sound power at no-load excitation ....................................................................... 12

4.3 Sound power of the cooling device(s) .................................................................. 12

4.4 Sound power due to load current ......................................................................... 12

5 Sound level measurement specification ........................................................................ 14

6 Instrumentation, calibration and accuracy ..................................................................... 15

7 Principal radiating surface ............................................................................................ 16

7.1 General ............................................................................................................... 16

7.2 Transformers with or without cooling device ......................................................... 16

7.3 Transformers in enclosures with cooling devices inside the enclosure .................. 16

7.4 Transformers in enclosures with cooling devices outside the enclosure ................ 17

7.5 Cooling devices mounted on a separate structure where the distance

between the two principal radiating surfaces is ≥ 3 m ........................................... 17

7.6 Dry-type transformers .......................................................................................... 17

7.7 Dry-type air-core reactors .................................................................................... 17

8 Prescribed contour ...................................................................................................... 18

9 Microphone positions ................................................................................................... 19

10 Calculation of the measurement surface area ............................................................... 19

10.1 Measurement surface area for measuring distances up to 30 m ............................ 19

10.2 Measurement surface area for measuring distances larger than 30 m ................... 19

11 Sound measurement .................................................................................................... 20

11.1 Test conditions .................................................................................................... 20

11.1.1 Placement of test object ............................................................................... 20

11.1.2 Test energisation options ............................................................................. 20

11.1.3 Test application details ................................................................................ 21

11.1.4 Prevailing ambient conditions ....................................................................... 21

11.2 Sound pressure method ...................................................................................... 21

11.2.1 General ....................................................................................................... 21

11.2.2 Test procedure ............................................................................................. 21

11.2.3 Calculation of the spatially averaged sound pressure level ............................ 22

11.2.4 Validation of test measurements with respect to background noise ................ 23

11.2.5 Calculation of environmental correction K ..................................................... 23

11.2.6 Final correction for steady-state background noise and test environment ....... 25

11.3 Sound intensity method ....................................................................................... 26

11.3.1 General ....................................................................................................... 26

11.3.2 Test procedure ............................................................................................. 26

11.3.3 Calculation of average normal sound intensity and sound pressure level ....... 27

11.3.4 Measurement validation ............................................................................... 28

11.3.5 Final correction based on P-I index and direction flag ................................... 28

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SIST EN 60076-10:2017
IEC 60076-10:2016  IEC 2016 – 3 –

12 Determination of sound power level by calculation ........................................................ 29

13 Logarithmic addition and subtraction of individual sound levels ..................................... 29

14 Far-field calculations for distances larger than 30 m ..................................................... 30

15 Presentation of results ................................................................................................. 31

Annex A (informative) Narrow-band and time-synchronous measurements .......................... 40

A.1 General considerations ........................................................................................ 40

A.2 Narrow-band measurement ................................................................................. 40

A.2.1 General ....................................................................................................... 40

A.2.2 Post processing of narrow-band measurements to exclude background

noise ........................................................................................................... 41

A.3 Time-synchronous averaging technique ............................................................... 41

Annex B (informative) Typical report of sound level determination ....................................... 42

B.1 Sound pressure method ...................................................................................... 42

B.2 Sound pressure method – Appendix for the point-by-point procedure.................... 50

B.3 Sound intensity method ....................................................................................... 51

B.4 Sound intensity method – Appendix for the point-by-point procedure .................... 59

Bibliography ....................................................................................................................... 60

Figure 1 – Typical microphone path / positions for sound measurement on

transformers excluding cooling devices ............................................................................... 33

Figure 2 – Typical microphone path / positions for sound measurement on transformers

having cooling devices mounted either directly on the tank or on a separate structure

spaced < 3 m away from the principal radiating surface of the main tank .............................. 34

Figure 3 – Typical microphone path / positions for sound measurement on transformers

having separate cooling devices spaced < 3 m away from the principal radiating

surface of the main tank ...................................................................................................... 35

Figure 4 – Typical microphone path / positions for sound measurement on cooling
devices mounted on a separate structure spaced ≥ 3 m away from the principal

radiating surface of the transformer ..................................................................................... 36

Figure 5 – Typical microphone positions for sound measurement on dry-type

transformers without enclosures .......................................................................................... 37

Figure 6 – Principle radiating surface and prescribed contour of dry-type air-core

reactors .............................................................................................................................. 38

Figure 7 – Environmental correction, K ................................................................................ 39

Table 1 – Test acceptance criteria ....................................................................................... 23

Table 2 – Approximate values of the average acoustic absorption coefficient ....................... 25

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SIST EN 60076-10:2017
– 4 – IEC 60076-10:2016  IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
POWER TRANSFORMERS –
Part 10: Determination of sound levels
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote

international co-operation on all questions concerning standardization in the electrical and electronic fields. To

this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,

Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC

Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested

in the subject dealt with may participate in this preparatory work. International, governmental and non-

governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely

with the International Organization for Standardization (ISO) in accordance with conditions determined by

agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence

between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

the latter.

5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 60076-10 has been prepared by IEC technical committee 14:

Power transformers

This second edition cancels and replaces the first edition published in 2001 and constitutes a

technical revision.

This edition includes the following significant technical changes with respect to the previous

edition:
– additional useful definitions introduced;

– definition of distribution type transformers introduced for the purpose this standard;

– new clause for sound level measurement specification introduced;

– requirement for 1/3 octave band measurements introduced for transformers other than

distribution type transformers;
---------------------- Page: 10 ----------------------
SIST EN 60076-10:2017
IEC 60076-10:2016  IEC 2016 – 5 –

– standard measurement distance changed from 0,3 m to 1 m for transformers other than

distribution type transformers;

– height of measurement surface is now clearly defined to count from the reflecting plane;

– measurement surface formula unified;
– correction criteria for intensity method introduced;
– rules for sound measurements on dry-type reactors introduced;
– figures revised;
– new informative test report templates introduced (Annex B);

– IEC 60076-10-1 (application guide) revised in parallel providing worthwhile information for

the use of this standard.
The text of this standard is based on the following documents:
FDIS Report on voting
14/846/FDIS 14/849/RVD

Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts in the IEC 60076 series, published under the general title Power

transformers, can be found on the IEC website.

The committee has decided that the contents of this publication will remain unchanged until

the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates

that it contains colours which are considered to be useful for the correct

understanding of its contents. Users should therefore print this document using a

colour printer.
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SIST EN 60076-10:2017
– 6 – IEC 60076-10:2016  IEC 2016
INTRODUCTION

One of many parameters considered when specifying, designing and placing transformers,

reactors and their associated cooling devices is the sound level that the equipment is likely to

emit under defined in-service conditions. This part of IEC 60076 provides the basis for the

specification and test of sound levels.

This standard describes in a logical sequence the loading conditions, how to specify and to

test as well as how to evaluate and report sound levels for the equipment under test. A new

section for the specification of sound levels has been introduced as Clause 5.

For the purpose of this standard, the definition “distribution type transformers” was

introduced. This reflects industry’s need to maintain simpler and faster sound measurements

for this category of transformers.

The new requirement for reporting 1/3-octave band spectra for all sound levels (including the

background noise) on units for installation in substations reflects the more onerous conditions

imposed by planning authorities on the purchaser and also the improved functionality of

modern instrumentation.

When the sound intensity method was introduced in this standard limited experience was

available. During subsequent years of operating this standard levels of experience have

significantly increased and necessary changes have become evident. The equivalence of the

pressure and the intensity methods has been demonstrated within certain test limitations.

The introduction of new validation criteria for the intensity method recognises these

limitations. The permissible pressure – intensity index ∆L remains 8 dB however the

difference between measured sound pressure level and reported sound intensity level is

limited to 4 dB.

For the pressure method the correction procedure for reflections has been enhanced by

recommending the application of frequency dependent K values derived by measurement of

the reverberation time of the test facility. Where K is derived from absorption coefficients the

table for the average absorption coefficients has been rationalised to represent surfaces likely

to be found in the working environment.

Walk-around procedure and point-by-point procedure are equally applicable. The walk-around

procedure reflects the evolution of working practice allowing more time efficient

measurements mainly on large units. For distribution type transformers and in special

situations (health and safety) the point-by-point procedure is more appropriate.

In order to mitigate near-field effects the preferred measurement distance is set to 1 m with

exceptions for distribution type transformers, small test facilities, situations with low

signal-to-noise ratio and for health and safety where the distance is maintained at 0,3 m.

One single formula for the calculation of the measurement surface area S has been introduced

because the former complexity could only result in differences always smaller than 1 dB.

All figures describing the measurement surface area have been revised to be in accordance

with the enveloping method for sound power determination. The height h is always measured

from the test facility floor regardless of the height of the supports beneath the test object

unless the test object is mounted on a support with a sufficiently large surface acting as

reflecting plane.

Additional figures explain the procedure for the determination of the measurement surface

area and the prescribed contour for a number of configurations of dry-type reactors.

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SIST EN 60076-10:2017
IEC 60076-10:2016  IEC 2016 – 7 –

When using this standard, it is recommended to frequently refer to the corresponding

application guide IEC 60076-10-1:2016 as it promotes understanding with important

background information and helpful details. IEC 60076-10 and IEC 60076-10-1 were revised

in parallel by the same maintenance team resulting in fully aligned documents.
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SIST EN 60076-10:2017
– 8 – IEC 60076-10:2016  IEC 2016
POWER TRANSFORMERS –
Part 10: Determination of sound levels
1 Scope

This Part of IEC 60076 defines sound pressure and sound intensity measurement methods

from which sound power levels of transformers, reactors and their associated cooling devices

are determined.

NOTE For the purposes of this standard, the term "transformer" frequently means "transformer or reactor".

The methods are applicable to transformers, reactors and their cooling devices – either fitted

to or separate from the transformer – as covered by the IEC 60076 and IEC 61378 series.

This standard is primarily intended to apply to measurements made at the factory. Conditions

on-site can be very different because of the proximity of objects, including other transformers.

Nevertheless, this standard is applied to the extent possible for on-site measurements.

2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and

are indispensable for its application. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60076-1:2011, Power transformers – Part 1: General
IEC 60076-8:1997, Power transformers – Part 8: Application guide

IEC 61043:1993, Electroacoustics – Instruments for the measurement of sound intensity –

Measurements with pairs of pressure sensing microphones
IEC 61672-1, Electroacoustics – Sound level meters – Part 1: Specifications

IEC 61672-2, Electroacoustics – Sound level meters – Part 2: Pattern evaluation tests

ISO 3382-2:2008, Acoustics – Measurement of room acoustic parameters – Part 2:
Reverberation time in ordinary rooms

ISO 3746:2010, Acoustics – Determination of sound power levels and sound energy levels of

noise sources using sound pressure – Survey method using an enveloping measurement

surface over a reflecting plane

ISO 9614-1:1993, Acoustics – Determination of sound power levels of noise sources using

sound intensity – Part 1: Measurement at discrete points

ISO 9614-2:1996, Acoustics – Determination of sound power levels of noise sources using

sound intensity – Part 2: Measurement by scanning
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SIST EN 60076-10:2017
IEC 60076-10:2016  IEC 2016 – 9 –
3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 60076-1, as well as

the following, apply.
3.1
sound pressure

fluctuating pressure superimposed on the static (barometric) pressure by the presence of

sound
Note 1 to entry: It is expressed in pascal, Pa.
3.2
sound pressure level

ten times the logarithm to the base 10 of the ratio of the square of the r.m.s. sound pressure

to the square of the reference sound pressure (p = 20 × 10 Pa)
Note 1 to entry: It is expressed in decibels, dB.
L = 10 ×lg (1)
3.3
sound intensity

vector quantity describing the magnitude and direction of the sound power flow per unit area

at a given position
Note 1 to entry: The unit is watts per square metre, W/m .
3.4
normal sound intensity

component of the sound intensity in the direction normal to a measurement surface

Note 1 to entry: By convention, normal sound intensity is counted positive if the energy flow is directed away from

the test object and negative if the energy flow is directed towards the test object.

3.5
normal sound intensity level

ten times the logarithm to the base 10 of the ratio of the r.m.s. normal sound intensity to the

–12 –2
reference sound intensity (I = 1 × 10 Wm )
Note 1 to entry: It is expressed in decibels, dB.
L = 10 × lg (2)

Note 2 to entry: Since I can be either positive or negative, a separate direction flag F for L to indicate the

n Dir I
direction of flow of energ
...

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