EN ISO 6926:2016
(Main)Acoustics - Requirements for the performance and calibration of reference sound sources used for the determination of sound power levels (ISO 6926:2016)
Acoustics - Requirements for the performance and calibration of reference sound sources used for the determination of sound power levels (ISO 6926:2016)
ISO 6926:2016 specifies the acoustical performance requirements for reference sound sources:
- temporal steadiness (stability) of the sound power output;
- spectral characteristics;
- directivity.
Temporal steadiness is defined in terms of the standard deviation of repeatability (see 5.2). The spectral characteristics can be verified in either a hemi-anechoic room or a reverberation test room from measurements of the frequency band sound power levels in accordance with this International Standard (see 5.4). The performance requirements on directivity index can only be verified in a hemi-anechoic room (see 5.5.)
ISO 6926:2016 also specifies procedures for providing level calibration data and uncertainty on a sound source intended for use as a reference sound source in terms of its sound power level under reference meteorological conditions as defined in Clause 4 in octave and in one-third-octave bands, and with frequency weighting A.
ISO 6926:2016 is titled as a calibration standard even though the method is conducted in a testing laboratory and the level calibration results are not directly traceable to national standards of measure in a strict metrological sense. Testing laboratories performing this method are not expected to meet all requirements normally associated with a calibration laboratory.
NOTE ISO/IEC 17025[15] specifies different requirements for the competence of testing laboratories and calibration laboratories respectively. Laboratories testing reference sound sources in accordance with this International Standard would typically comply with the requirements for testing laboratories but not necessarily with those for calibration laboratories.
ISO 6926:2016 specifies methods to calibrate reference sound sources not only in a free field over a reflecting plane but also in reverberation test rooms at different distances from the boundary surfaces. For the position of the reference sound source on one reflecting plane, the two different test environments mentioned above are considered equivalent for frequency bands above or equal to 200 Hz. At 160 Hz and below, some systematic differences can occur (see 11.2). For frequencies below 100 Hz, an alternative calibration method using sound intensity is given.
The sound source can either be placed directly on the floor or mounted on a stand to be used at a certain elevation above the floor. According to this International Standard, stand-mounted sources are calibrated in reverberation test rooms. Floor-mounted sources are either calibrated in hemi-anechoic or in reverberation test rooms. For floor-mounted sources in hemi-anechoic rooms, this International Standard is valid only for sources whose maximum vertical dimension is less than 0,5 m and whose maximum horizontal dimension is less than 0,8 m. According to this International Standard, only floor-mounted reference sound sources can be used when carrying out measurements on a measurement surface. For reference sound sources to be used or calibrated under reverberant conditions, no such restrictions on maximum dimensions apply.
Akustik - Anforderungen an die Eigenschaften und die Kalibrierung von Vergleichsschallquellen für die Bestimmung von Schallleistungspegeln (ISO 6926:2016)
Diese Internationale Norm legt Anforderungen an die akustischen Eigenschaften von Vergleichsschallquellen fest:
— zeitliche Konstanz (Stabilität) der Schallleistungsabgabe;
— spektrale Eigenschaften;
— Richtcharakteristik.
Die zeitliche Konstanz ist als Wiederholstandardabweichung definiert (siehe 5.2). Die spektralen Eigenschaften können entweder in einem reflexionsarmen Halbraum oder in einem Hallraum auf der Grundlage von Messungen der Schallleistungspegel in Frequenzbändern nach dieser Internationalen Norm verifiziert werden (siehe 5.4). Die Anforderungen an die Eigenschaften des Richtwirkungsmaßes können nur in einem reflexionsarmen Halbraum verifiziert werden (siehe 5.5).
In dieser Internationalen Norm sind außerdem Verfahren zur Bereitstellung von Daten zur Pegelkalibrierung und zur Bestimmung der Unsicherheit einer Schallquelle festgelegt, die hinsichtlich ihres Schallleistungspegels unter den in Abschnitt 4 definierten meteorologischen Bezugsbedingungen in Oktav- und Terzbändern und mit der Frequenzbewertung A für den Einsatz als Vergleichsschallquelle vorgesehen ist.
Die vorliegende Internationale Norm wird als Kalibriernorm bezeichnet, obwohl das Verfahren in einem Prüflaboratorium (Prüfstand) durchgeführt wird und die Ergebnisse der Pegelkalibrierung nicht direkt im strengen messtechnischen Sinne auf nationale Messnormale rückführbar sind. Von den Prüflaboratorien, die dieses Verfahren durchführen, wird nicht erwartet, dass sie alle Anforderungen erfüllen, die üblicherweise an ein Kalibrierlaboratorium gestellt werden.
ANMERKUNG ISO/IEC 17025 [15] legt verschiedene Anforderungen an die Kompetenz von Prüflaboratorien und Kalibrierlaboratorien fest. Laboratorien, in denen Vergleichsschallquellen nach dieser Internationalen Norm geprüft werden, erfüllen typischerweise die Anforderungen an Prüflaboratorien, nicht jedoch notwendigerweise diejenigen an Kalibrierlaboratorien.
Diese Internationale Norm legt Verfahren für die Kalibrierung von Vergleichsschallquellen nicht nur im Freifeld über einer reflektierenden Ebene, sondern auch in Hallräumen bei verschiedenen Abständen zu den Begrenzungsflächen fest. Für die Position der Vergleichsschallquelle auf einer reflektierenden Ebene werden die beiden vorstehend genannten Prüfumgebungen für Frequenzbänder ab mindestens 200 Hz als gleichwertig angesehen. Bei 160 Hz und darunter können gewisse systematische Unterschiede auftreten (siehe 11.2). Für Frequenzen unterhalb von 100 Hz ist ein alternatives Kalibrierverfahren unter Anwendung der Schallintensität angegeben.
Die Schallquelle kann entweder direkt auf dem Boden aufgestellt oder zur Verwendung in einer bestimmten Höhe über dem Boden an einem Ständer befestigt werden. Nach dieser Internationalen Norm werden an einem Ständer befestigte Quellen in Hallräumen kalibriert. Auf dem Boden aufgestellte Quellen werden entweder in reflexionsarmen Halbräumen oder in Hallräumen kalibriert. Bei auf dem Boden aufgestellten Schallquellen in reflexionsarmen Halbräumen ist diese Internationale Norm nur für Schallquellen, deren größtes vertikales Maß weniger als 0,5 m und deren größtes horizontales Maß weniger als 0,8 m beträgt, anwendbar. Nach dieser Internationalen Norm können für Messungen auf einer Messfläche nur auf dem Boden aufgestellte Vergleichsschallquellen verwendet werden. Für Vergleichsschallquellen, die bei halligen Bedingungen verwendet oder kalibriert werden sollen, gelten die genannten Einschränkungen für die Höchstmaße nicht.
Acoustique - Prescriptions relatives aux performances et à l'étalonnage des sources sonores de référence pour la détermination des niveaux de puissance acoustique (ISO 6926:2016)
ISO 6926:2016 spécifie les exigences relatives aux performances acoustiques des sources sonores de référence:
- stabilité dans le temps de la puissance acoustique émise;
- caractéristiques spectrales;
- directivité.
La stabilité dans le temps est définie en termes d'écart-type de répétabilité (voir 5.2). Les caractéristiques spectrales peuvent être vérifiées soit dans une salle semi-anéchoïque, soit dans une salle d'essai réverbérante, à partir du mesurage des niveaux de puissance acoustique par bande de fréquences conformément à la présente Norme internationale (voir 5.4). Les exigences de performance relatives à l'indice de directivité ne peuvent être vérifiées que dans une salle semi-anéchoïque (voir 5.5).
ISO 6926:2016 définit également des modes opératoires pour obtenir les données et l'incertitude de l'étalonnage des niveaux d'une source sonore destinée à être utilisée comme source sonore de référence, le résultat étant exprimé par un niveau de puissance acoustique par bandes d'octave et de tiers d'octave, et avec la pondération fréquentielle A, dans les conditions météorologiques de référence telles que définies à l'Article 4.
ISO 6926:2016 est appelée norme d'étalonnage bien que la méthode soit applicable dans un laboratoire d'essai et que les résultats de l'étalonnage des niveaux ne se rapportent pas directement à des normes nationales de mesure dans un sens métrologique strict. Il n'est pas attendu que les laboratoires d'essai appliquant cette méthode satisfassent à toutes les exigences normalement associées à un laboratoire d'étalonnage.
NOTE L'ISO/IEC 17025[15] spécifie différentes exigences pour les compétences respectives des laboratoires d'essai et des laboratoires d'étalonnage. Les laboratoires qui soumettent à l'essai des sources sonores de référence conformément à la présente Norme internationale doivent normalement se conformer aux exigences des laboratoires d'essai, mais pas nécessairement à celles des laboratoires d'étalonnage.
ISO 6926:2016 spécifie des méthodes d'étalonnage pour les sources sonores de référence non seulement en champ libre au-dessus d'un plan réfléchissant, mais aussi dans des salles d'essais réverbérantes à diverses distances des surfaces délimitantes. Pour la position de la source sonore de référence au-dessus d'un plan réfléchissant unique, les deux environnements d'essai différents mentionnés ci-dessus sont considérés comme équivalents pour les bandes de fréquences supérieures ou égales à 200 Hz. À 160 Hz et au-dessous, des écarts systématiques peuvent exister (voir 11.2). Pour les fréquences inférieures à 100 Hz, une autre méthode d'étalonnage utilisant l'intensité acoustique est donnée.
La source sonore peut être conçue spécifiquement soit pour être posée directement sur le sol, soit pour être montée sur un support afin d'être utilisée à une certaine distance du sol. Conformément à la présente Norme internationale, les sources montées sur un support sont étalonnées dans des salles d'essai réverbérantes. Les sources au sol sont étalonnées dans des salles d'essai semi-anéchoïques ou réverbérantes. Pour des sources au sol en salles semi-anéchoïques, la présente Norme internationale s'applique uniquement aux sources dont la dimension verticale maximale est inférieure à 0,5 m et dont la dimension horizontale maximale est inférieure à 0,8 m. Conformément à la présente Norme internationale, seules les sources sonores de référence posées au sol peuvent être utilisées pour eff
Akustika - Zahteve za lastnosti in umerjanje referenčnih virov zvoka pri ugotavljanju ravni zvočnih moči (ISO 6926:2016)
Ta mednarodni standard določa zahteve glede akustičnih lastnosti za referenčne vire zvoka:
– časovna stalnost (stabilnost) izhoda zvočne moči;
– spektralne značilnosti;
– usmerjenost.
Časovna stalnost je določena v smislu standardnega odklona ponovljivosti (glej točko 5.2). Spektralne značilnosti je mogoče potrditi v polgluhem prostoru ali v prostoru za preizkus odmevov iz meritev ravni zvočne moči v frekvenčnem pasu skladno s tem mednarodnim standardom (glej točko 5.4). Zahteve glede lastnosti v zvezi z indeksom usmerjenosti je mogoče potrditi le v polgluhem prostoru (glej točko 5.5).
Ta mednarodni standard določa tudi postopke za zagotavljanje podatkov za umerjanje ravni in negotovosti pri zvočnem viru, namenjenem za uporabo kot referenčni zvočni vir v smislu njegove ravni zvočne moči pod referenčnimi meteorološkimi pogoji, kot je določeno v točki 4 za oktavne in terčne pasove ter s frekvenčnim vrednotenjem A.
Ta mednarodni standard je poimenovan kot standard umerjanja, čeprav je metoda izvedena v laboratoriju za preskušanje in iz rezultatov umerjanja ravni ni mogoče neposredno ugotoviti državnih standardov mere v strogem meroslovnem smislu. Od laboratorijev za preskušanje, ki uporabljajo to metodo, se ne pričakuje izpolnjevanje vseh zahtev, ki so običajno povezane z laboratoriji za umerjanje.
OPOMBA: Standard ISO/IEC 17025[15] določa različne zahteve za usposobljenost laboratorijev za preskušanje in umerjanje. Laboratoriji, kjer se preskušajo referenčni viri zvoka v skladu s tem mednarodnim standardom, so običajno skladni z zahtevami za laboratorije za preskušanje, ne pa nujno z zahtevami za laboratorije za umerjanje.
Ta mednarodni standard določa metode za umerjanje referenčnih virov zvoka ne le v prostem polju nad odsevno ravnino, temveč tudi v prostorih za preskus odmevov pri različnih razdaljah od mejnih površin. Za položaj referenčnega vira zvoka na eni odsevni ravnini se zgoraj omenjeni različni okolji preskusa štejeta kot enakovredni pri frekvenčnih pasovih 200 Hz ali višjih. Pri 160 Hz in nižjih vrednostih je mogoče, da pride do nekaterih sistemskih razlik (glej točko 11.2). Za frekvence pod 100 Hz je na voljo drugačna metoda umerjanja z intenzivnostjo zvoka.
Zvočni vir je mogoče postaviti neposredno na tla ali na stojalo, ki se uporablja na določeni višini. Po tem mednarodnem standardu se viri na stojalu umerjajo v prostorih za preskus odmevov. Viri na tleh se umerjajo v polgluhih prostorih ali prostorih za preskus odmevov. Pri talnih virih v polgluhih prostorih ta mednarodni standard velja le za vire, katerih največja navpična dolžina je manjša od 0,5 m, največja vodoravna dolžina pa manjša od 0,8 m. Po tem mednarodnem standardu je mogoče pri izvajanju meritev na površini za merjenje uporabljati le talne referenčne vire zvoka. Za referenčne vire zvoka, ki se bodo uporabljali ali umerjali v prostoru, kjer je prisoten odmev, takšne omejitve ali največje dolžine ne veljajo.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-april-2016
1DGRPHãþD
SIST EN ISO 6926:2002
$NXVWLND=DKWHYH]DODVWQRVWLLQXPHUMDQMHUHIHUHQþQLKYLURY]YRNDSUL
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Acoustics - Requirements for the performance and calibration of reference sound
sources used for the determination of sound power levels (ISO 6926:2016)
Akustik - Anforderungen an die Eigenschaften und die Kalibrierung von
Vergleichsschallquellen für die Bestimmung von Schallleistungspegeln (ISO 6926:2016)
Acoustique - Prescriptions relatives aux performances et à l'étalonnage des sources
sonores de référence pour la détermination des niveaux de puissance acoustique (ISO
6926:2016)
Ta slovenski standard je istoveten z: EN ISO 6926:2016
ICS:
17.140.01 $NXVWLþQDPHUMHQMDLQ Acoustic measurements and
EODåHQMHKUXSDQDVSORãQR noise abatement in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN ISO 6926
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2016
EUROPÄISCHE NORM
ICS 17.140.01 Supersedes EN ISO 6926:2001
English Version
Acoustics - Requirements for the performance and
calibration of reference sound sources used for the
determination of sound power levels (ISO 6926:2016)
Acoustique - Prescriptions relatives aux performances Akustik - Anforderungen an die Eigenschaften und die
et à l'étalonnage des sources sonores de référence pour Kalibrierung von Vergleichsschallquellen für die
la détermination des niveaux de puissance acoustique Bestimmung von Schallleistungspegeln (ISO
(ISO 6926:2016) 6926:2016)
This European Standard was approved by CEN on 26 December 2015.
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
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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2016 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 6926:2016 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
European foreword
This document (EN ISO 6926:2016) 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 August 2016, and conflicting national standards shall
be withdrawn at the latest by August 2016.
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 6926:2001.
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, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 6926:2016 has been approved by CEN as EN ISO 6926:2016 without any modification.
INTERNATIONAL ISO
STANDARD 6926
Third edition
2016-01-15
Acoustics — Requirements for the
performance and calibration of
reference sound sources used for the
determination of sound power levels
Acoustique — Prescriptions relatives aux performances et à
l’étalonnage des sources sonores de référence pour la détermination
des niveaux de puissance acoustique
Reference number
ISO 6926:2016(E)
©
ISO 2016
ISO 6926:2016(E)
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, 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 the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
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ii © ISO 2016 – All rights reserved
ISO 6926:2016(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 2
4 Reference meteorological conditions . 4
5 Performance requirements . 5
5.1 General . 5
5.2 Temporal steadiness (stability) of sound power output . . 5
5.3 Total broadband sound power level . 5
5.4 Spectral characteristics. 5
5.5 Directivity . 6
5.6 Recalibration . 6
6 Instrumentation . 7
6.1 General . 7
6.2 Microphone in a hemi-anechoic room . 7
6.3 Microphone in a reverberation test room . 7
6.4 Microphone frequency response correction . 7
6.5 Verification . 8
6.6 Microphone calibration check . 8
7 Installation and operation of the reference sound source during calibration .8
7.1 General . 8
7.2 Requirements in hemi-anechoic rooms . 9
7.3 Requirements in reverberation rooms . 9
8 Calibration procedure in hemi-anechoic rooms . 9
8.1 Test environment . 9
8.2 Microphone positions . 9
8.2.1 General. 9
8.2.2 Meridional paths . 9
8.2.3 Spiral path. 9
8.2.4 Fixed point array . 9
8.2.5 Coaxial circular paths . 9
8.3 Measurements .10
8.3.1 General.10
8.3.2 Directivity index .10
8.3.3 Temporal steadiness .10
8.4 Calculations .11
9 Calibration procedure in reverberation test rooms .12
9.1 Test environment .12
9.2 Microphone positions .12
9.3 Measurements .12
9.3.1 General.12
9.3.2 Temporal steadiness .13
9.4 Calculations .13
10 Alternative calibration procedure at low frequencies .13
11 Measurement uncertainty .13
11.1 General .13
11.2 Typical values of the reproducibility standard deviation .14
12 Information to be recorded .15
ISO 6926:2016(E)
13 Information to be reported .15
Annex A (informative) Guidance on the determination of C .16
Annex B (normative) Alternative calibration procedure at low frequencies .18
Bibliography .19
iv © ISO 2016 – All rights reserved
ISO 6926:2016(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.
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 documents 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).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.
This third edition cancels and replaces the second edition (ISO 6926:1999), which has been technically
revised with the following changes:
— the clause on measurement uncertainty has been updated with stricter reference to
ISO/IEC Guide 98-3 and moved backwards in the standard to be more in line with ISO 3745;
— the corrections for meteorological conditions have been brought in line with ISO 3745 and a new
Annex A on the acoustic radiation impedance correction has been introduced;
— an alternative method using sound intensity for low frequency calibration in hemi-anechoic rooms
not fully qualified for low frequencies has been introduced in a new Annex B.
ISO 6926:2016(E)
Introduction
Reference sound sources are used extensively in “comparison methods” for determining the noise
emissions of physically stationary sound sources. A reference sound source, of known sound power
output, is used to establish the numerical relationship between the sound power level of a source, in a
given location in a given acoustic environment and the space- and time-averaged sound pressure level
at a set of microphone positions. Once that relationship is established, it is straightforward to measure
the average sound pressure level produced by an “unknown source” and to determine the sound power
level produced by that source.
This International Standard defines the important physical and performance characteristics of
reference sound sources and specifies procedures for their calibration, primarily to determine the
sound power level of other sound sources.
This International Standard supplements a group or family of International Standards, the ISO 3740
group, which describes various methods for determining the sound power levels of machines
and equipment. This group of International Standards specifies the acoustical requirements for
measurements that are appropriate for different test environments.
Five International Standards in the ISO 3740 group include procedures in which a reference sound
source is used: ISO 3741, ISO 3743-1, ISO 3744, ISO 3746 and ISO 3747. ISO 3740 gives guidelines for the
use of all the International Standards in the group.
Note that the sound power output of reference sound sources will vary, in particular at low frequencies,
with the distance from the source to nearby reflecting planes. Sound power data of reference sound
sources are thus valid only for the position used during the calibration.
In addition to being useful for determining sound power levels by the comparison method, reference
sound sources can be used for qualification tests on an acoustic environment and to estimate the
influence of an acoustic environment on the sound pressure levels produced by one or more sound
sources located in that environment. Examples of International Standards referring to reference sound
sources with these applications are ISO/TR 11690-3 and ISO 14257. Requirements other than those of
this International Standard can be applicable in these cases.
vi © ISO 2016 – All rights reserved
INTERNATIONAL STANDARD ISO 6926:2016(E)
Acoustics — Requirements for the performance and
calibration of reference sound sources used for the
determination of sound power levels
1 Scope
This International Standard specifies the acoustical performance requirements for reference sound
sources:
— temporal steadiness (stability) of the sound power output;
— spectral characteristics;
— directivity.
Temporal steadiness is defined in terms of the standard deviation of repeatability (see 5.2). The
spectral characteristics can be verified in either a hemi-anechoic room or a reverberation test room
from measurements of the frequency band sound power levels in accordance with this International
Standard (see 5.4). The performance requirements on directivity index can only be verified in a hemi-
anechoic room (see 5.5.)
This International Standard also specifies procedures for providing level calibration data and
uncertainty on a sound source intended for use as a reference sound source in terms of its sound power
level under reference meteorological conditions as defined in Clause 4 in octave and in one-third-octave
bands, and with frequency weighting A.
This International Standard is titled as a calibration standard even though the method is conducted in
a testing laboratory and the level calibration results are not directly traceable to national standards of
measure in a strict metrological sense. Testing laboratories performing this method are not expected
to meet all requirements normally associated with a calibration laboratory.
[15]
NOTE ISO/IEC 17025 specifies different requirements for the competence of testing laboratories and
calibration laboratories respectively. Laboratories testing reference sound sources in accordance with this
International Standard would typically comply with the requirements for testing laboratories but not necessarily
with those for calibration laboratories.
This International Standard specifies methods to calibrate reference sound sources not only in a
free field over a reflecting plane but also in reverberation test rooms at different distances from the
boundary surfaces. For the position of the reference sound source on one reflecting plane, the two
different test environments mentioned above are considered equivalent for frequency bands above or
equal to 200 Hz. At 160 Hz and below, some systematic differences can occur (see 11.2). For frequencies
below 100 Hz, an alternative calibration method using sound intensity is given.
The sound source can either be placed directly on the floor or mounted on a stand to be used at a
certain elevation above the floor. According to this International Standard, stand-mounted sources are
calibrated in reverberation test rooms. Floor-mounted sources are either calibrated in hemi-anechoic
or in reverberation test rooms. For floor-mounted sources in hemi-anechoic rooms, this International
Standard is valid only for sources whose maximum vertical dimension is less than 0,5 m and whose
maximum horizontal dimension is less than 0,8 m. According to this International Standard, only floor-
mounted reference sound sources can be used when carrying out measurements on a measurement
surface. For reference sound sources to be used or calibrated under reverberant conditions, no such
restrictions on maximum dimensions apply.
ISO 6926:2016(E)
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.
ISO 3741:2010, Acoustics — Determination of sound power levels and sound energy levels of noise sources
using sound pressure — Precision methods for reverberation test rooms
ISO 3744:2010, Acoustics — Determination of sound power levels and sound energy levels of noise sources
using sound pressure — Engineering methods for an essentially free field over a reflecting plane
ISO 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 9613-1:1993, Acoustics — Attenuation of sound during propagation outdoors — Part 1: Calculation of
the absorption of sound by the atmosphere
ISO 9614-3, Acoustics — Determination of sound power levels of noise sources using sound intensity —
Part 3: Precision method for measurement by scanning
IEC 60942:2003, Electroacoustics — Sound calibrators
IEC 61094-1, Measurement microphones — Part 1: Specifications for laboratory standard microphones
IEC 61094-4, Measurement microphones — Part 4: Specifications for working standard microphones
IEC 61183, Electroacoustics — Random-incidence and diffuse-field calibration of sound level meters
IEC 61260-1, Electroacoustics — Octave-band and fractional-octave-band filters — Part 1: Specifications
IEC 61672-1, Electroacoustics — Sound level meters — Part 1: Specifications
IEC 61672-3:2013, Electroacoustics — Sound level meters — Part 3: Periodic tests
IEC 62585, Electroacoustics — Methods to determine corrections to obtain the free-field response of a
sound level meter
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
reference sound source
RSS
portable, generally electroacoustical or aerodynamic sound source or other noise-generating device,
and associated control circuitry giving a broadband stable output complying with the requirements of
this International Standard
3.2
free sound field over a reflecting plane
sound field in a homogeneous, isotropic medium in the half-space above an infinite, reflecting plane in
the absence of other reflecting obstacles
3.3
hemi-anechoic room
test room in which a free sound field over a reflecting plane is obtained
2 © ISO 2016 – All rights reserved
ISO 6926:2016(E)
3.4
reverberation test room
test room meeting the requirements of ISO 3741
3.5
measurement surface
hypothetical surface of area, S, on which the microphone positions are located at which the sound
pressure levels are measured, enveloping the source under test and, in the case of a hemi-anechoic
room, terminating on the reflecting plane on which the source is located
Note 1 to entry: The measurement surface area is expressed in metres squared.
3.6
surface sound pressure level
L
p
energy-average of the time-averaged sound pressure levels at all the microphone positions, or traverses,
on the measurement surface, with the background noise corrections, K , applied at each microphone
position or traverse
Note 1 to entry: Surface sound pressure level is expressed in decibels.
Note 2 to entry: For definition and calculation of K , see ISO 3745.
3.7
sound power level
L
W
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
P
L =10lg dB
W
P
where the reference value, P , is 1 pW
Note 1 to entry: If a specific frequency weighting as specified in IEC 61672–1, and/or specific frequency bands are
applied, this should be indicated by appropriate subscripts; e.g. L denotes the A-weighted sound power level.
WA
[17]
Note 2 to entry: This definition is technically in accordance with ISO 80000-8:2007, 8-23.
[SOURCE: ISO/TR 25417:2007, 2.9]
3.8
measurement radius
r
radius of a hemi-spherical measurement surface
3.9
directivity index
D
Ii
measure of the extent to which a source radiates sound in a particular direction, relative to the mean
sound radiation over the measurement surface, where for fixed microphones, the direction is from
the source to the position of the microphone, and for traverses, the direction is from the source to the
position along the microphone path at which the highest sound pressure level is recorded
Note 1 to entry: The directivity index of direction, i, is calculated from measurements in a hemi-anechoic room
by the following formula:
DL=−L
Ii pi p
where
ISO 6926:2016(E)
L is the sound pressure level for each one-third-octave band at the ith
pi
microphone position on the measurement surface, in decibels;
L is the maximum sound pressure level for each one-third-octave
pi
band that is recorded during the ith microphone traverse (see 8.2) on the measurement sur-
face, in decibels;
is the surface sound pressure level averaged over the same measurement surface, in decibels.
L
p
Note 2 to entry: With the above ”operational“ definition, the directivity index is a measure of the uniformity of
sound radiation from the source over the particular measurement surface being employed and as it is installed in
the test environment. Definitions for the “theoretical” directivity index appearing in textbooks and the literature
usually represent the uniformity of sound radiation by comparing the source under test in its test environment to
a point source of the same sound power radiating into a full sphere in a totally free field. When such definitions are
applied to sources located in a free field above a reflecting plane, they include a constant “+3 dB” to account for the
hemispherical radiation. Care should be taken when comparing or using different definitions of directivity index.
3.10
frequency range of interest
frequency range of one-third-octave bands with nominal mid-band frequencies from 100 Hz to 10 000 Hz
Note 1 to entry: The frequency range of interest in one-third-octave bands may be extended up to as much as
20 000 Hz or down to as low as 50 Hz, provided the requirements of this International Standard are still met.
3.11
comparison method
method in which the sound power level is calculated by comparing the measured sound pressure levels
produced by the source under test in an environment with the sound pressure levels produced by a
reference sound source of known sound power output in the same environment
3.12
direct method
method in reverberation test rooms where the sound power level is calculated using the equivalent
sound absorption area determined from measurements of the reverberation time
3.13
reverberation time
T
time that is required for the sound pressure level to decrease by 60 dB after the sound source has stopped
Note 1 to entry: If the reverberation time is evaluated from the decay of the first 10 dB or 15 dB, it is denoted T
or T , respectively.
Note 2 to entry: It is expressed in seconds.
3.14
repeatability condition
condition where independent test results are obtained with the same method on identical test items in
the same laboratory by the same operator using the same equipment within short intervals of time
4 Reference meteorological conditions
Reference meteorological conditions for the purpose of calculating the sound power level, corresponding
−3
to a reference characteristic acoustic impedance of air ρc = 411,5 Nsm (where ρ is the density of air
and c is the speed of sound) are the following:
air temperature: 23,0 °C;
static pressure: 1,013 25 × 10 Pa;
4 © ISO 2016 – All rights reserved
ISO 6926:2016(E)
relative humidity: 50 %.
5 Performance requirements
5.1 General
A manufacturer may only state that its RSS is in compliance with this International Standard if all of the
requirements laid out in this Clause are met.
5.2 Temporal steadiness (stability) of sound power output
The sound power level of the reference sound source shall be stable over time such that the measured
standard deviations under repeatability conditions, σ (see 8.3.3 and 9.3.2), do not exceed those
r
given in Table 1.
Table 1 — Maximum value of the standard deviation of the sound power level under repeatability
conditions for a reference sound source in accordance with this International Standard
Standard deviation
One-third-octave
under repeatability
midband frequency
conditions, σ
r
Hz
dB
50 to 80 0,8
100 to 160 0,4
200 to 20 000 0,2
NOTE 1 For special purposes, a reference sound source may have a more limited frequency range.
A reference sound source meeting the requirements of this International Standard shall include
information on the range of variation of the source of electrical or mechanical power (e.g. the line
voltage) within which the sound power level in any one-third-octave band within the frequency range
of interest shall not vary by more than ±0,3 dB.
NOTE 2 The sound power level of a reference sound source depends on the static pressure and the air temperature.
For the RSS to be used at different temperatures or altitudes, it is expected that information concerning appropriate
corrections, and their uncertainties, for the influence of air temperature and static pressure on sound power
emitted by the RSS, is included. For an aerodynamic fan RSS, the rotational speed and variations due to changing
meteorological conditions during the qualification test are found according to 8.4 and 9.4.
5.3 Total broadband sound power level
There are no specific requirements placed on the total broadband sound power level produced by
the RSS. However, if the total broadband sound power level is reported, either as an unweighted or
frequency-weighted quantity, the corresponding frequency range shall also be reported.
5.4 Spectral characteristics
The RSS shall produce broadband steady sound over the frequency range in which it is intended for
use, but at least for one-third-octave midband frequencies between 100 Hz and 10 000 Hz. Over this
frequency range, all of the one-third-octave-band sound power levels, when measured in conformity
with the requirements of Clause 8 and Clause 9, as applicable, shall be within a range of 12 dB. Under
these same measuring conditions, and over this same frequency range, the sound power level in each
one-third-octave band shall not deviate by more than 3 dB from the sound power level in the adjacent
higher or lower one-third-octave bands (the higher band only in the case of the 100 Hz band, and the
lower band only in the case of the 10 000 Hz band). If the frequency range is extended beyond 100 Hz to
10 000 Hz, then the requirements for the extended range are 16 dB and 4 dB, respectively.
ISO 6926:2016(E)
It may be desirable for special sound sources to meet these criteria over a more limited frequency
range or for a different spectrum shape. However, if a RSS does not comply with the requirements of
this International Standard over at least the frequency range from 100 Hz to 10 000 Hz, it shall not be
labelled or declared as being in compliance with the frequency range of this International Standard.
5.5 Directivity
The highest value of the directivity index of the source in any one-third-octave band with midband
frequency between 100 Hz and 10 000 Hz shall not exceed +6 dB when measured in a hemi-anechoic
room complying with Clause 8.
If the RSS is to be used exclusively in reverberation test rooms complying with ISO 3741, these
requirements do not apply but in that case, the RSS shall be labelled “For use as a reference sound
source in reverberation test rooms complying with ISO 3741”.
5.6 Recalibration
5.6.1 Whenever any mechanical damage has been inflicted on the reference sound source, it shall be
recalibrated. For aerodynamic sound sources, measure the rotational speed (RPM) of the fanwheel. If
the present RPM after a few minutes stabilization deviates less than 1% from that found during the last
calibration, then the RSS is not electrically damaged.
5.6.2 The user manual for the reference sound source should provide the recommended maximum
time interval between successive calibrations such that changes in the sound power levels of the
specified model of the reference sound source is not expected to exceed 2,83 times the values in Table 1
(presumably from qualified historical tracking by the manufacturer). If this time interval is provided, it
shall be considered a requirement of this International Standard. If it is not provided in the user manual,
the maximum time interval shall be two years.
NOTE If the difference between two consecutive calibrations is less than 2,83 times the standard deviation,
[7]
there is, e.g. see ISO 5725-2 , a probability of 95 % that the temporal stability of the RSS complies with the
values given in Table 1.
5.6.3 In order to determine whether or not recalibration of a reference sound source is necessary
before the maximum time interval has expired, one-third-octave-band sound pressure levels shall be
measured regularly at one or more fixed reference points with the source operating at a specific location
in a specified test environment as a check of its temporal stability. The user manual for the reference
sound source should specify the time interval between such regular measurements. If this time interval
is provided, it shall be considered a requirement of this International Standard. If it is not provided in the
user manual, the time interval shall be a maximum of six months. If, after using manufacturer-specified
procedures to adjust the measured sound pressure levels to constant environmental conditions when
necessary, changes in any one-third-octave-band sound pressure level between successive checks exceed
2,83 times the values in Table 1, the reference sound source shall be recalibrated.
NOTE If the above check indicates the need for recalibration, confidence may be diminished in any data that
may have been taken with the reference sound source during the intervening time interval. In view of this, the
laboratory may decide on a much shorter time interval, or select a variable time interval based on the number of
tests it performs.
5.6.4 For laboratories using a reference sound source in a generally fixed location, in a controlled
environment without transporting it, calibration intervals may be extended beyond the maximum time
interval in 5.6.2 if changes in the surface time average band sound pressure levels measured at a maximum
of one-year intervals over positions 1 to 10 of ISO 3744:2010, Table B.1, using a fixed measurement radius
of at least 1 m, in an environment that has been qualified for broadband sound power level determination
in accordance with ISO 3745:2012, Annex A do not exceed 2,83 times the values in Table 1. Alternatively,
an equivalent test may be carried out with the RSS in one specified location in a reverberation room
following the procedures specified for measurements of sound pressure levels from a RSS in ISO 3741.
For this measurement, the reference sound source shall each time be measured at the same temperature,
6 © ISO 2016 – All rights reserved
ISO 6926:2016(E)
pressure, and humidity within the tolerances specified in ISO 3741. The change in sound pressure levels
is hereby defined as the difference between the latest measurement and a reference measurement using
exactly the same test procedure that was carried out in connection with the arrival of the reference sound
source directly after the latest accredited calibration in full compliance with this International Standard.
Each check shall be documented.
However, the maximum permissible extension using this procedure is 10 years. After this period,
the reference sound source shall be subject to a new calibration by an authorized laboratory in full
compliance with this International Standard.
6 Instrumentation
6.1 General
For measurements conducted with a sound level meter, the instrument for measuring sound pressure
levels, including microphone(s) as well as cable(s), windscreen(s), recording devices and other
accessories, if used, shall meet the requirements of IEC 61672-1 for a class 1 sound level meter.
For measurements conducted using computerized data acquisition systems the complete measurement
system, including hardware and software components, shall be validated in accordance with the
periodic test requirements of IEC 61672-3. The validation shall be conducted for the requirements
specified in IEC 61672-3:2013, Clauses 8, 9, 10, 11, 14, 15, 16, 17, 18, and 20 at conditions that are
representative of those present in the environment where the measurements are conducted.
Proportional octave band filters for sound level meters or computerized data acquisition systems shall
meet the requirements of IEC 61260-1, class 1.
6.2 Microphone in a hemi-anechoic room
Use either a microphone with a nominally flat frequency response at normal incidence mounted with the
axis of the microphone (that runs perpendicular through the plane of the diaphragm) pointing towards
the centre of the measurement hemisphere, or a microphone with a nominally flat frequency response at
grazing incidence mounted with the axis of the microphone perpendicular to the line pointing towards
the centre of the measurement hemisphere. Microphones used as part of a sound level meter shall meet
the requirements of IEC 61672-1 for a class 1 sound level meter. Microphones used with computerized
data acquisition systems shall be of type LS or WS and shall have free field (F), pressure (P), or diffuse
field (D) response as defined by IEC 61094-1 and IEC 61094-4 respectively. Microphones shall be
validated in accordance with the periodic testing requirements of IEC 61672- 3:2013 for a class 1 sound
level meter and be individually frequency-corrected according to 6.4.
6.3 Microphone in a reverberation test room
Microphones used as a part of a sound level meter shall be of random incidence type (or corrected
to random incidence) and shall be calibrated in accordance with IEC 61183 and shall meet the
requirements of IEC 61672-1 for a class 1 sound level meter. Microphones used with computerized
data acquisition systems shall be of type WS and shall have diffuse field (D) response as defined by
IEC 61094-4. Microphones shall be validated in accordance with the periodic testing requirements of
IEC 61672-3 for a class 1 sound level meter and be individually frequency-corrected according to 6.4.
6.4 Microphone frequency response correction
Microphones for use in hemi-anechoic rooms shall
...
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