SIST EN ISO 26101-2:2024

SLOVENSKI STANDARD
01-september-2024
Akustika - Preskusne metode za kvalifikacijo akustičnega okolja - 2. del: Določanje
okoljskih popravkov (ISO 26101-2:2024)
Acoustics - Test methods for the qualification of the acoustic environment - Part 2:
Determination of the environmental correction (ISO 26101-2:2024)
Akustik - Prüfverfahren zur Qualifizierung der akustischen Umgebung - Teil 2:
Bestimmung der Umgebungskorrektur (ISO 26101-2:2024)
Acoustique - Méthodes d’essai pour la qualification de l'environnement acoustique -
Partie 2: Détermination de la correction d’environnement (ISO 26101-2:2024)
Ta slovenski standard je istoveten z: EN ISO 26101-2:2024
ICS:
17.140.01 Akustična merjenja in Acoustic measurements and
blaženje hrupa na splošno noise abatement in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 26101-2
EUROPEAN STANDARD
NORME EUROPÉENNE
June 2024
EUROPÄISCHE NORM
ICS 17.140.01
English Version
Acoustics - Test methods for the qualification of the
acoustic environment - Part 2: Determination of the
environmental correction (ISO 26101-2:2024)
Acoustique - Méthodes d'essai pour la qualification de Akustik - Prüfverfahren zur Qualifizierung der
l'environnement acoustique - Partie 2: Détermination akustischen Umgebung - Teil 2: Bestimmung der
de la correction d'environnement (ISO 26101-2:2024) Umgebungskorrektur (ISO 26101-2:2024)
This European Standard was approved by CEN on 2 June 2024.

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-CENELEC 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-CENELEC Management
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United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 26101-2:2024 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 26101-2:2024) has been prepared by Technical Committee ISO/TC 43
"Acoustics" in collaboration with Technical Committee CEN/TC 211 “Acoustics” the secretariat of which
is held by DIN.
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 December 2024, and conflicting national standards
shall be withdrawn at the latest by December 2024.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
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, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 26101-2:2024 has been approved by CEN as EN ISO 26101-2:2024 without any
modification.
International
Standard
ISO 26101-2
First edition
Acoustics — Test methods for
2024-06
the qualification of the acoustic
environment —
Part 2:
Determination of the environmental
correction
Acoustique — Méthodes d’essai pour la qualification de
l'environnement acoustique —
Partie 2: Détermination de la correction d’environnement
Reference number
ISO 26101-2:2024(en) © ISO 2024

ISO 26101-2:2024(en)
© ISO 2024
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
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or ISO’s member body in the country of the requester.
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Phone: +41 22 749 01 11
Email: copyright@iso.org
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Published in Switzerland
ii
ISO 26101-2:2024(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Qualification procedures for the acoustic environment . 3
4.1 General .3
4.2 Absolute comparison test .3
4.3 Methods based on room absorption . .3
4.4 Inverse-square-law qualification of parallelepiped and cylindrical measurement
surfaces .3
4.5 Approximate method based on an estimation of the equivalent absorption area.3
5 Absolute comparison test . 4
5.1 General .4
5.2 Locations of reference sound source in test environment .5
5.3 Information to be recorded and reported .5
6 Determination of the environmental correction based on room absorption . 6
6.1 General .6
6.2 Reverberation method .6
6.3 Two-surface method .6
6.4 Determination of the equivalent absorption area with a reference sound source (direct
method) .7
6.5 Information to be recorded and reported .8
7 Inverse-square-law qualification of parallelepiped and cylindrical measurement
surfaces . 8
7.1 General .8
7.2 Qualification criteria .9
7.2.1 General .9
7.2.2 Maximum allowable deviations from inverse square law.9
7.2.3 Frequency range to be qualified .9
7.2.4 Maximum qualified volume .9
7.3 Installation of test sound sources and microphone traverses .10
7.3.1 Test sound source requirements .10
7.3.2 Test sound source location .10
7.3.3 Microphone traverse paths for parallelepiped and cylindrical measurement
surfaces .10
7.4 Test procedure . 12
7.4.1 Analysis bandwidth . 12
7.4.2 Generation of sound . . 12
7.4.3 Spatial resolution of the measurement points . 12
7.5 Information to be recorded and reported . 13
8 Approximate method based on an estimation of the equivalent absorption area.13
8.1 General . 13
8.2 Information to be recorded and reported . 13
Annex A (informative) Uncertainty of the environmental correction . 14
Bibliography .15

iii
ISO 26101-2:2024(en)
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.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise, in
collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC
211, Acoustics, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna
Agreement).
A list of all parts in the ISO 26101 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
ISO 26101-2:2024(en)
Introduction
This document is one of the series ISO 26101, which specify various methods for qualifying the acoustic
environment. The methods specified in this document permit the qualification of an acoustic environment
that approximates to an acoustic free field near one or more reflecting planes. In other words, an acoustic
environment in which the effect of reflected sound on sound pressure level measurements is sufficiently
small, so that it can be corrected for with the so-called environmental correction K . K can be needed to
2 2
[3]
determine the sound power level, see e.g. ISO 3744 or ISO 3746 , or the emission sound pressure level, see
[6] [7] [8]
e.g. ISO 11201 , ISO 11202 and ISO 11204 .
It is expected that the qualification procedures outlined in this document will be referred to by other
International Standards and industry test codes. In such cases, these documents making reference to this
document can specify qualification criteria based on the environmental correction K determined according
to this document.
v
International Standard ISO 26101-2:2024(en)
Acoustics — Test methods for the qualification of the acoustic
environment —
Part 2:
Determination of the environmental correction
1 Scope
This document specifies methods for qualifying an environment that approximates to an acoustic free field
near one or more reflecting planes. The goal of the qualification is to determine the environmental correction
K , which is used to correct for reflected sound when 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 such an environment.
In practice, the K value determined will be a function of both the reflected sound from the test environment
and the shape and size of the measurement surface used for the K determination. For the purposes of this
document and the documents that refer to it, the differences between K values determined with different
measurement surfaces are assumed to be included in the stated measurement uncertainty for the test method.
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.
ISO 3744:2024, Acoustics — Determination of sound power levels of noise sources using sound pressure —
Engineering methods for an essentially free field over a reflecting plane
ISO 3745:2012, Acoustics — Determination of sound power levels and sound energy levels of noise sources using
sound pressure — Precision methods for anechoic rooms and hemi-anechoic rooms
ISO 6926, Acoustics — Requirements for the performance and calibration of reference sound sources used for
the determination of sound power levels
ISO 26101-1, Acoustics — Test methods for the qualification of the acoustic environment — Part 1: Qualification
of free-field environments
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 3744 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/

ISO 26101-2:2024(en)
3.1
reverberation time
T
〈room acoustic parameters〉 duration required for the space-averaged sound energy density in an enclosure
to decrease by 60 dB after the source emission has stopped
Note 1 to entry: Reverberation time, T, is expressed in seconds.
Note 2 to entry: T can be evaluated based on a smaller dynamic range than 60 dB and extrapolated to a decay time of
60 dB. It is then labelled accordingly. Thus, if T is derived from the time at which the decay curve first reaches 5 dB
and 25 dB below the initial level, it is labelled T . If decay values of 5 dB to 35 dB below the initial level are used, it is
labelled T .
[1]
[SOURCE: ISO 3382-2:2008 , 3.5]
3.2
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
[SOURCE: ISO 3744:2024, 3.12]
3.3
environmental correction
K
correction applied to the mean (energy average) sound pressure levels over all the microphone positions on
the measurement surface (3.2), to account for the influence of reflected or absorbed sound
Note 1 to entry: Environmental correction, K , is expressed in decibels.
Note 2 to entry: 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 overall A-weighting is denoted
2f
K , which is determined from A-weighted sound pressure level measurements.
2A
Note 3 to entry: In general, the environmental correction depends on the area of the measurement surface and usually
K increases with S.
[SOURCE: ISO 3744:2024, 3.15, modified “determined as described in Annex A or in ISO 26101-2:2024“ and
“Note 4 to entry” have been omitted.]
3.4
sound absorption coefficient
α
at a given frequency and for specified conditions, the relative fraction of sound power incident upon a surface
which is not reflected
[2]
[SOURCE: ISO 3741:2010 , 3.9, modified — The NOTE has been deleted.]
3.5
equivalent absorption area
A
product of the area and sound absorption coefficient (3.4) of a surface
Note 1 to entry: A hypothetical surface area with a sound absorption coefficient of 1,0 that would have the same total
sound absorption as the test environment that is being qualified.
[2]
[SOURCE: ISO 3741:2010 , 3.10, modified term “sound” has been omitted and the NOTE has been replaced
by a Note 1 to entry with different content.]

ISO 26101-2:2024(en)
4 Qualification procedures for the acoustic environment
4.1 General
Environmental influences shall be evaluated by selecting one of four qualification procedures (see 4.2 to
4.5) used to determine the magnitude of the environmental correction K . These qualification procedures
shall be used to determine if any undesired environmental influences are present and to qualify a given
measurement surface for an actual noise source under test in accordance with this document. Information
on the uncertainty of the environmental correction can be found in Annex A.
4.2 Absolute comparison test
The absolute comparison test (see Clause 5) is carried out with a reference sound source (RSS) and may
be used outdoors and indoors. This is the preferred procedure for qualifying a test environment according
to ISO 3744, particularly if data in frequency bands are required, and if the noise source under test can be
removed from the test site. However, it may also be used, if the noise source under test cannot be removed
from the test site (see 5.2). This method is expected to yield the most accurate results in typical industrial
[9]
environments .
4.3 Methods based on room absorption
The methods based on room absorption (see Clause 6) require the determination of the equivalent
absorption area, A , of the test room and can be less accurate than the absolute comparison test in typical
industrial environments. These tests are based on the assumption that the room has approximately a cubic
shape, is substantially empty, and that sound is absorbed at the room boundaries only. Three methods are
specified in which A is calculated either from measurements of reverberation time (see 6.2), from
measurements of sound pressure levels from the noise source under test using a secondary measurement
surface (see 6.3) or from measurements on a reference sound source (see 6.4).
4.4 Inverse-square-law qualification of parallelepiped and cylindrical measurement
surfaces
This third qualification procedure (see Clause 7) may be used to qualify hemi-anechoic test rooms for
parallelepiped or cylindrical measurement surfaces up to a maximum volume (qualification with the goal
K = 0 ). It is the preferred method to qualify a hemi-anechoic room and represents the most accurate
method. To qualify an anechoic or a hemi-anechoic chamber for hemi-spherical measurement surfaces, see
ISO 26101-1 and ISO 3745.
NOTE In hemi-anechoic rooms, the other qualification procedures can yield unreliable results.
4.5 Approximate method based on an estimation of the equivalent absorption area
This method (see Clause 8) is based on an estimation of the equivalent absorption area A of the test room
and is considered to be the least accurate method.
Figure 1 is a flowchart which provides guidance for the selection of a method to determine the environmental
correction K . The method specified in Clause 5 may be used indoors and outdoors, while the methods
specified in Clauses 6 and 8 may be used indoors only. As indicated in Figure 1, the inverse-square law
method according to Clause 7 may be used in hemi-anechoic chambers only.
NOTE In some industrial buildings, which are of low height and have reflecting surfaces, the sound propagation
can be distorted. In these conditions, the qualification procedures according to Clause 6 and Clause 8 might not be
applicable.
ISO 26101-2:2024(en)
Figure 1 — Flowchart to select a method to determine K
5 Absolute comparison test
5.1 General
This method represents the preferred method to determine the environmental correction according to
ISO 3744:2024, Annex A.
ISO 26101-2:2024(en)
A reference sound source meeting the requirements of ISO 6926 shall be mounted in the test environment,
in essentially the same position as that of the noise source under test. The sound power level of the reference
sound source shall be determined in accordance with the procedure of ISO 3744:2024, Clause 8 without the
environmental correction, K (i.e. K is initially assumed to be equal to zero). The measurement surface
2 2
used for the qualification measurements and K determination shall encompass microphone positions on
the measurement surface to be used for the measurements of the noise source under test.
The environmental correction, K , is given by Formula (1):
*
KL=−L (1)
2 WW()RSS
where
*
is the environmentally uncorrected sound power level of the reference sound source, determined
L
W
in accordance with ISO 3744:2024,
...