Electroacoustics - Instruments for measurement of aircraft noise - Performance requirements for systems to measure sound pressure levels in noise certification of aircraft

IEC 61265:2018 specifies requirements for the electroacoustical performance of systems of instruments used to measure sound for the purposes of aircraft noise certification, and for other comparisons among aircraft models, and provides methods by which tests can be made periodically to verify that the performance continues to conform to the requirements within stated limits. In general, a sound measurement system for this purpose comprises a combination of instruments extending from a microphone, including its windscreen and other accessories, through data recording and processing devices to a suitable output. Different measurement systems, regardless of their composition, perform the necessary functions in different ways and operate on either analogue or digital principles. IEC 61265:2018 cancels and replaces the first edition published in 1995. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) addition of guidance for measurements for aircraft other than large transport aeroplanes; b) addition of microphones used in ground plane measurement systems; c) addition of weighted sound level measurements other than one-third-octave band measurements, for certain aircraft types; d) revision and clarification of requirements for digital audio recording; e) addition of requirements for evaluation of measurement uncertainty.

Elektroakustik - Geräte zur Messung des Geräuschs von Luftfahrzeugen - Anforderungen an die Eigenschaften von Systemen zur Messung von Schalldruckpegeln bei der Zertifizierung von Luftfahrzeugen

Électroacoustique - Instruments pour la mesure du bruit des aéronefs - Exigences relatives aux systèmes de mesure des niveaux de pression acoustique pour la certification acoustique des aéronefs

IEC 61265:2018 spécifie les caractéristiques électroacoustiques des systèmes instrumentaux utilisés pour la mesure des bruits dans le cadre de la certification acoustique des aéronefs, ainsi que pour l'établissement d'autres comparaisons entre des modèles d'aéronefs, et fournit des méthodes d'essais de vérification périodique qui permettent de s'assurer du maintien des caractéristiques en conformité avec les exigences, à l'intérieur de tolérances spécifiées. En général, un système de mesure utilisé à cet effet se compose d'une combinaison d'instruments allant du microphone, y compris son écran anti-vent et ses autres accessoires, en passant par des dispositifs d'enregistrement et de traitement des données, jusqu'à un dispositif de sortie approprié. Les différents systèmes de mesure, indépendamment de leur composition, réalisent les fonctions nécessaires de différentes façons et fonctionnent suivant des principes analogiques ou numériques. IEC 61265:2018 annule et remplace la première édition parue en 1995. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente: a) ajout de recommandations pour les mesures d'aéronefs autres que des gros avions de transport; b) ajout de microphones utilisés dans les systèmes de mesure à plan de sol; c) ajout de mesures de niveau acoustique pondéré, autres que les mesures par bandes de tiers d'octave, pour certains types d'aéronefs; d) révision et clarification des exigences applicables à l'enregistrement audio numérique; e) ajout d'exigences pour l'évaluation de l'incertitude de mesure.

Elektroakustika - Instrumenti za merjenje hrupa zrakoplova - Zahteve za delovanje sistemov za merjenje zvočnega tlaka pri certificiranju hrupa zrakoplova (IEC 61265:2018)

Ta dokument določa zahteve za elektroakustično zmogljivost sistemov instrumentov, ki se uporabljajo za merjenje zvoka pri certificiranju hrupa zrakoplova in za druge primerjave med modeli zrakoplovov, ter določa metode, s katerimi je mogoče redno izvajati preskuse, s katerimi se preverja, ali zmogljivost še naprej ustreza zahtevam.
Na splošno sistem za merjenje zvoka za ta namen obsega kombinacijo instrumentov, ki zajema vse od mikrofona, vključno z njegovimi filtri in drugimi dodatki, do naprav za zapisovanje in obdelavo podatkov na ustrezen izhod. Različni merilni sistemi, ne glede na sestavo, opravljajo potrebne funkcije na različne načine in delujejo s pomočjo analognih ali digitalnih načel.

General Information

Status
Published
Publication Date
16-Aug-2018
Technical Committee
Drafting Committee
Current Stage
6060 - Document made available
Due Date
17-Aug-2018
Completion Date
17-Aug-2018

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SLOVENSKI STANDARD
SIST EN IEC 61265:2018
01-oktober-2018
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SIST EN 61265:2002

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Electroacoustics - Instruments for measurement of aircraft noise - Performance

requirements for systems to measure sound pressure levels in noise certification of

aircraft (IEC 61265:2018)
Ta slovenski standard je istoveten z: EN IEC 61265:2018
ICS:
17.140.50 Elektroakustika Electroacoustics
49.020 Letala in vesoljska vozila na Aircraft and space vehicles in
splošno general
SIST EN IEC 61265:2018 en

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

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SIST EN IEC 61265:2018
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SIST EN IEC 61265:2018
EUROPEAN STANDARD EN IEC 61265
NORME EUROPÉENNE
EUROPÄISCHE NORM
August 2018
ICS 17.140.50; 49.020 Supersedes EN 61265:1995
English Version
Electroacoustics - Instruments for measurement of aircraft noise
- Performance requirements for systems to measure sound
pressure levels in noise certification of aircraft
(IEC 61265:2018)

Électroacoustique - Instruments pour la mesure du bruit des Elektroakustik - Geräte zur Messung des Geräuschs von

aéronefs - Exigences relatives aux systèmes de mesure Luftfahrzeugen - Anforderungen an die Eigenschaften von

des niveaux de pression acoustique pour la certification Systemen zur Messung von Schalldruckpegeln bei der

acoustique des aéronefs Zertifizierung von Luftfahrzeugen
(IEC 61265:2018) (IEC 61265:2018)

This European Standard was approved by CENELEC on 2018-06-12. 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, Serbia, 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: Rue de la Science 23, B-1040 Brussels

© 2018 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Ref. No. EN IEC 61265:2018 E
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SIST EN IEC 61265:2018
EN IEC 61265:2018
European foreword

The text of document 29/958/CDV, future edition 2 of IEC 61265, prepared by IEC/TC 29

"Electroacoustics" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as

EN IEC 61265:2018.
The following dates are fixed:
(dop) 2019-03-12
• 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 (dow) 2021-06-12
standards conflicting with the
document have to be withdrawn
This document supersedes EN 61265:1995.

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

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

Endorsement notice

The text of the International Standard IEC 61265:2018 was approved by CENELEC as a European

Standard without any modification.

In the official version, for Bibliography, the following notes have to be added for the standards indicated:

IEC 61094-4 NOTE Harmonized as EN 61094-4.
IEC 61326-1:2012 NOTE Harmonized as EN 61326-1:2013 (not modified).
IEC 61000-4-2 NOTE Harmonized as EN 61000-4-2.
IEC 61000-4-3 NOTE Harmonized as EN 61000-4-3.
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SIST EN IEC 61265:2018
EN IEC 61265:2018
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements 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.

NOTE 1 Where 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 60942 - Electroacoustics - Sound calibrators EN IEC 60942 -
IEC 61260-1 - Electroacoustics - Octave-band and EN 61260-1 -
fractional-octave-band filters -
Part 1: Specifications
IEC 61672-1 - Electroacoustics - Sound level meters - EN 61672-1 -
Part 1: Specifications
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SIST EN IEC 61265:2018
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SIST EN IEC 61265:2018
IEC 61265
Edition 2.0 2018-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electroacoustics – Instruments for measurement of aircraft noise – Performance
requirements for systems to measure sound pressure levels in noise
certification of aircraft
Électroacoustique – Instruments pour la mesure du bruit des aéronefs –
Exigences relatives aux systèmes de mesure des niveaux de pression
acoustique pour la certification acoustique des aéronefs
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.140.50; 49.020 ISBN 978-2-8322-5695-4

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 IEC 61265:2018
– 2 – IEC 61265:2018 © IEC 2018
CONTENTS

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

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

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 7

3 Terms and definitions ...................................................................................................... 7

4 Purpose ......................................................................................................................... 11

5 Requirements ................................................................................................................ 12

5.1 General ................................................................................................................. 12

5.1.1 Output data ................................................................................................... 12

5.1.2 Time-pressure history .................................................................................... 12

5.1.3 Measurements of sound from aircraft ground power units .............................. 12

5.1.4 Measurements of aircraft operations on the ground ....................................... 12

5.2 Measurement uncertainty ...................................................................................... 12

5.2.1 Relationship with regulatory requirements ..................................................... 12

5.2.2 Performance verification ................................................................................ 13

5.2.3 Periodic tests ................................................................................................. 13

5.3 Reference environmental conditions ..................................................................... 13

5.4 Sound calibrator.................................................................................................... 13

5.5 Microphone system ............................................................................................... 13

5.5.1 Pressure and free-field type microphones ...................................................... 13

5.5.2 Grazing incidence microphone configuration .................................................. 14

5.5.3 Ground plane microphone configuration ......................................................... 15

5.5.4 Measurement configurations .......................................................................... 16

5.6 Measurement system exclusive of the microphone ................................................ 16

5.6.1 Frequency response ...................................................................................... 16

5.6.2 Level linearity ................................................................................................ 16

5.6.3 Floating-range measurement systems ........................................................... 17

5.7 Spectrum analysis system ..................................................................................... 17

5.7.1 Third-octave analysis ..................................................................................... 17

5.7.2 Time constants .............................................................................................. 17

5.7.3 Time offset .................................................................................................... 17

5.7.4 Anti-aliasing................................................................................................... 18

5.8 Readout device resolution ..................................................................................... 18

5.9 Sensitivity to various environments ....................................................................... 18

5.9.1 General ......................................................................................................... 18

5.9.2 Atmospheric pressure .................................................................................... 18

5.9.3 Air temperature .............................................................................................. 18

5.9.4 Humidity ........................................................................................................ 19

5.9.5 Electromagnetic compatibility ........................................................................ 19

Annex A (informative) Methods of testing the electroacoustical performance of a

measurement system ............................................................................................................ 20

A.1 General ................................................................................................................. 20

A.2 Operating conditions for test ................................................................................. 20

A.3 Sound calibrator.................................................................................................... 20

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IEC 61265:2018 © IEC 2018 – 3 –

A.4 Microphone system frequency response ............................................................... 20

A.5 Frequency response of the measurement system exclusive of the

microphone ........................................................................................................... 21

A.6 Linear operating range of the measurement system exclusive of the

microphone ........................................................................................................... 21

A.7 Spectrum analysis system ..................................................................................... 21

Annex B (informative) Relationship between tolerance interval, corresponding

acceptance interval and the maximum permitted uncertainty of measurement ....................... 22

Bibliography .......................................................................................................................... 24

Figure 1 – Illustration of sound incidence angles from the principal axis of the

microphone ........................................................................................................................... 15

Figure B.1 – Relationship between tolerance interval, corresponding acceptance

interval and the maximum permitted uncertainty of measurement ......................................... 22

Table 1 – ICAO measurement protocols (informative) ........................................................... 11

Table 2 – Maximum difference between the free-field sensitivity level of a microphone

used in grazing-incidence microphone configuration at normal incidence and at

specified sound incidence angles .......................................................................................... 15

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SIST EN IEC 61265:2018
– 4 – IEC 61265:2018 © IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTROACOUSTICS – INSTRUMENTS FOR MEASUREMENT OF
AIRCRAFT NOISE – PERFORMANCE REQUIREMENTS FOR
SYSTEMS TO MEASURE SOUND PRESSURE LEVELS
IN NOISE CERTIFICATION OF AIRCRAFT
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 61265 has been prepared by IEC technical committee 29:

Electroacoustics.

This second edition cancels and replaces the first edition published in 1995. This edition

constitutes a technical revision.

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

edition:

a) addition of guidance for measurements for aircraft other than large transport aeroplanes;

b) addition of microphones used in ground plane measurement systems;

c) addition of weighted sound level measurements other than one-third-octave band

measurements, for certain aircraft types;
d) revision and clarification of requirements for digital audio recording;
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SIST EN IEC 61265:2018
IEC 61265:2018 © IEC 2018 – 5 –
e) addition of requirements for evaluation of measurement uncertainty.
The text of this International Standard is based on the following documents:
CDV Report on voting
29/958/CDV 29/980A/RVC

Full information on the voting for the approval of this International Standard can be found in

the report on voting indicated in the above table.

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

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

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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SIST EN IEC 61265:2018
– 6 – IEC 61265:2018 © IEC 2018
INTRODUCTION

IEC 61265 provides requirements for the electroacoustical performance of instruments for

measurement of the sound produced by aircraft in flight or on the ground, or by an aircraft

engine installed on an outdoor test stand, for the purposes of demonstrating compliance with

aircraft noise certification limits established by relevant national aviation authorities and for

other comparisons among aircraft models. The instruments can be components of a complete

measurement system. Methods are also indicated by which the performance of such
instruments can be tested periodically.

Measurement and data-analysis procedures for aircraft noise certification are described in

Volume I of Annex 16 to the Convention on International Civil Aviation, with further guidance

and descriptions of acceptable "equivalent procedures" given in the Environmental Technical

Manual prepared by the Committee on Aviation Environmental Protection (CAEP) of the

International Civil Aviation Organization (ICAO). Together these documents are referred to in

this document as "ICAO Annex 16". The procedures include measurement and analysis of the

sound from aircraft in operation, and, in some circumstances, of the sound from static engines

and engines under test, under given operating and atmospheric conditions.

Several of the requirements given in this document differ from the requirements of

IEC 61672-1 for sound level meters, especially concerning the frequency and directional

response, linear operating range and sensitivity to various environments. Many of these

differences are due to the requirement for uniform response at a wide range of angles of

sound arrival as an aircraft moves through the certification test flight. If the output signal from

a measurement system conforming to this document is processed to yield an overall sound

pressure level from all frequency bands, the level derived can differ from that obtained from a

sound level meter conforming to IEC 61672-1.

Systems in accordance with this document are used to perform measurements meeting the

requirements of ICAO Annex 16 or a certifying authority’s specific procedures to demonstrate

that a given aircraft complies with the limits for noise level near the ground over the course of

a test flight. Uncertainty of each measurement is considered when establishing the test

procedures, and it is not the intent of this document to duplicate the confidence interval

analysis inherent in the noise flight test procedure.
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SIST EN IEC 61265:2018
IEC 61265:2018 © IEC 2018 – 7 –
ELECTROACOUSTICS – INSTRUMENTS FOR MEASUREMENT OF
AIRCRAFT NOISE – PERFORMANCE REQUIREMENTS FOR
SYSTEMS TO MEASURE SOUND PRESSURE LEVELS
IN NOISE CERTIFICATION OF AIRCRAFT
1 Scope

This document specifies requirements for the electroacoustical performance of systems of

instruments used to measure sound for the purposes of aircraft noise certification, and for

other comparisons among aircraft models, and provides methods by which tests can be made

periodically to verify that the performance continues to conform to the requirements within

stated limits.

In general, a sound measurement system for this purpose comprises a combination of

instruments extending from a microphone, including its windscreen and other accessories,

through data recording and processing devices to a suitable output. Different measurement

systems, regardless of their composition, perform the necessary functions in different ways

and operate on either analogue or digital principles.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their

content constitutes requirements 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.
IEC 60942, Electroacoustics – Sound calibrators

IEC 61260-1, Electroacoustics – Octave-band and fractional-octave-band filters – Part 1:

Specifications
IEC 61672-1, Electroacoustics – Sound level meters – Part 1: Specifications
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
calibration record

time-pressure history or recorded value obtained during a calibration procedure, consisting of

a measurement system output while its acoustic input is provided by a sound calibrator

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3.2
effective perceived noise level
EPNL
EPNdB

single number evaluator of the subjective effects of aircraft noise on human beings,

expressed in decibels (EPNdB) as described in ICAO Annex 16, Appendix I
Note 1 to entry: This note applies to the French language only.
3.3
floating-range measurement system
measurement system incorporating automatic level range switching
3.4
free-field microphone

microphone having substantially uniform frequency response to plane progressive sound

waves arriving at angles substantially normal to the plane of the microphone diaphragm

3.5
free-field sensitivity

quotient of the root-mean-square voltage at the output of a microphone

system by the root-mean-square sound pressure that would exist at the position of the

microphone in the absence of the microphone, for a sinusoidal plane progressive sound wave

of specified frequency, at a specified sound-incidence angle
Note 1 to entry: The free-field sensitivity is expressed in volts per pascal.
3.6
free-field sensitivity level

twenty times the logarithm to the base ten of the ratio of the free-field

sensitivity to the reference sensitivity of one volt per pascal
Note 1 to entry: The free-field sensitivity level is expressed in decibels.

Note 2 to entry: The free-field sensitivity level can be determined by subtracting the sound pressure level (re

20 μPa expressed in dB) of the sound incident on the microphone from the voltage level (re 1 V expressed in dB) at

the output of the microphone system, and adding 93,98 dB to the result.
3.7
grazing incidence

condition where sound from the source of interest impinges on the microphone primarily at an

incidence angle parallel to the plane of the microphone diaphragm
3.8
ASmax

maximum value obtained during a given time period or event of A-frequency-weighted, S-time-

weighted sound pressure level
3.9

sound exposure level (SEL) of the time integral of squared A-weighted sound pressure over a

given time period or event, with reference to the square of the reference sound pressure of 20

µPa, and a reference duration of one second, as provided by an integrating sound level meter

in accordance with ICAO Annex 16, Appendix 4
Note 1 to entry: L is expressed in decibels.

EXAMPLE L is the sound energy of an acoustic event lasting one second that is equal to the sound energy of

the measured event over the time interval that the A-weighted sound pressure level is within 10 dB of its maximum

value. It is typically 7 dB to 12 dB higher than the L during the same interval.
Amax
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IEC 61265:2018 © IEC 2018 – 9 –
3.10
level difference

measured one-third-octave band output signal level on any level range, adjusted for the

difference between the settings of the level range controls on the level range and the

reference level range, minus the level of the corresponding electrical input signal

Note 1 to entry: The level difference is expressed in decibels.
3.11
level non-linearity

level difference on any level range, at a selected one-third-octave mid-band frequency, minus

the reference level difference, all input and output signals being relative to the same

reference quantity
Note 1 to entry: The level non-linearity is expressed in decibels.
3.12
level range

setting of the controls provided in a measurement system for the recording and level

measurement or spectral analysis of a sound pressure input signal
Note 1 to entry: The level range is expressed in decibels.
3.13
linear operating range

range of levels of steady sinusoidal electrical signals applied to the input of a measurement

system exclusive of the microphone system, extending from a lower boundary to an upper

boundary, over which the level non-linearity is within limits specified in 5.6.2

Note 1 to entry: The linear operating range applies to a stated level range and is expressed in decibels.

3.14
measurement system

combination of instruments used for the measurement of sound pressure levels, including a

sound calibrator, microphone system, signal recording and conditioning devices, and one third

octave band spectrum analysis or A-frequency-weighted, S-time-weighted sound level

measurement as required for the aircraft type being evaluated

Note 1 to entry: The measurement system covered by this document does not include analysis means for

computing metrics such as EPNL (EPNdB) or SEL (L ).

Note 2 to entry: Practical installations can include a number of microphone systems, the outputs from which are

recorded simultaneously by a multi-channel recording device. The signal recording and conditioning devices and/or

the spectrum analysis system can have separate channels in parallel, again with facilities for selection, either of

the input or of the output. For the purposes of this document, each combination of a single microphone system and

a single data-recording and data-analysis channel within the other instruments comprises a separate, complete

measurement system, and the requirements apply accordingly.
3.15
microphone

electroacoustic transducer converting audio-frequency air pressure variations to AC voltage

Note 1 to entry: Microphones used for aircraft noise certification are typically of the electrostatic or "condenser"

type which have an output impedance requiring a preamplifier to be located adjacent to the microphone rather than

in external equipment connected to the microphone by a cable.
3.16
micro
...

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