SIST EN ISO 3744:2026

Acoustics - Determination of sound power levels of noise sources using sound pressure - Engineering methods for an essentially free field over a reflecting plane (ISO 3744:2025, including corrected version 2026-01)

1.1        General
This document specifies methods for determining the sound power level of a noise source from sound pressure levels measured on a surface enveloping the noise source (machinery or equipment) in an environment that approximates to an acoustic free field near one or more reflecting planes. The sound power level produced by the noise source, in frequency bands or with A-weighting applied, is calculated using those measurements.
NOTE   Differently shaped measurement surfaces can yield differing estimates of the sound power level of a given noise source which are accounted for in the uncertainty associated with this test method. An appropriately drafted noise test code (see ISO 12001) gives detailed information on the selection of the surface.
1.2        Types of noise and noise sources
The methods specified in this document are suitable for all types of noise (steady, non-steady, and fluctuating) as defined in ISO 12001, except for short duration, impulsive events.
This document is applicable to all types and sizes of noise source (e.g. stationary or slowly moving component or sub-assembly), provided that the conditions for the measurements can be met.
NOTE   It is possible that the conditions for measurements given in this document are impracticable for very tall or very long sources such as chimneys, ducts, conveyors and multi-source industrial plants. A noise test code for the determination of noise emission of specific sources can provide alternative methods in such cases.
1.3        Test environment
The test environments that are applicable for measurements made in accordance with this document can be located indoors or outdoors, with one or more sound-reflecting planes present on or near which the noise source under test is mounted. The ideal environment is a completely open space with no bounding or reflecting surfaces other than the reflecting plane(s), such as that provided by a qualified hemi-anechoic chamber, but procedures are given for applying corrections (within limits that are specified) in the case of environments that are less than ideal. Annex A or ISO 26101-2 specifies methods for determining the adequacy of the test environment and for determination of corrections to be applied to account for the effect of the test environment.
1.4        Measurement uncertainty
Information is given on the uncertainty of the sound power levels determined in accordance with this document, for measurements made in limited bands of frequency and with frequency A-weighting applied. Annex I specifies procedures for testing laboratories that can be used to reduce measurement uncertainty. The uncertainty conforms to ISO 12001, accuracy grade 2 (engineering grade). General information on measurement uncertainty is provided in this document and additional information can be found in ISO 5114-1[8].

Akustik - Bestimmung der Schallleistungs- und Schallenergiepegel von Geräuschquellen aus Schalldruckmessungen - Hüllflächenverfahren der Genauigkeitsklasse 2 für ein im Wesentlichen freies Schallfeld über einer reflektierenden Ebene (ISO 3744:2025, korrigierte Fassung 2026-01)

1.1   Allgemeines
Dieses Dokument legt Verfahren für die Bestimmung des Schallleistungspegels einer Geräuschquelle aus Schalldruckpegeln fest, die auf einer Fläche gemessen werden, die die Geräuschquelle (eine Maschine oder ein Gerät) umschließt (Hüllfläche), wobei sich die Geräuschquelle in einer Umgebung befindet, die angenähert einem akustischen Freifeld in der Nähe einer oder mehrerer reflektierender Ebenen entspricht. Der an der Geräuschquelle, in Frequenzbändern oder durch A-Bewertung, erzeugte Schallleistungspegel wird durch diese Messungen berechnet.
ANMERKUNG   Unterschiedlich geformte Messflächen können unterschiedliche Schätzwerte des Schallleistungspegels einer bestimmten Geräuschquelle ergeben, die durch die Unsicherheit dieses Prüfverfahrens berücksichtigt werden. Eine ordnungsgemäß erstellte Geräuschmessnorm (siehe ISO 12001) enthält Einzelheiten zur Auswahl der Oberfläche.
1.2   Arten des Geräusches und der Geräuschquellen
Die in diesem Dokument festgelegten Verfahren eignen sich für alle in ISO 12001 definierten Geräuscharten (gleichförmige, ungleichförmige und schwankende), mit Ausnahme von kurzzeitigen, impulshaltigen Ereignissen.
Dieses Dokument gilt für Geräuschquellen aller Art und Größe (z. B. eine stationäre oder sich langsam fortbewegende Komponente oder Baugruppe), sofern die Messbedingungen erfüllt werden können.
ANMERKUNG   Die in diesem Dokument beschriebenen Messbedingungen können in der Praxis bei sehr hohen oder sehr langen Geräuschquellen wie Schornsteinen, Kanälen, Förderbändern und Industrieanlagen mit vielen Geräuschquellen möglicherweise zu Schwierigkeiten führen. In solchen Fällen können in einer Geräuschmessnorm für die Bestimmung der Geräuschemission solcher speziellen Quellen alternative Verfahren angegeben sein.
1.3   Messumgebung
Als Umgebung zur Durchführung von Messungen nach diesem Dokument eignet sich ein Ort in einem geschlossenen Raum oder im Freien, der eine oder mehrere schallreflektierende Ebenen aufweist, auf der oder in deren Nähe die zu untersuchende Geräuschquelle angeordnet wird. Die ideale Umgebung ist ein vollständig offener Raum mit keinen anderen Begrenzungs- oder Reflexionsflächen als der (den) reflektierenden Ebene(n) (wie zum Beispiel ein qualifizierter reflexionsarmer Halbraum), jedoch werden für den Fall von nichtidealen Umgebungen auch Verfahren zur Anwendung von Korrekturen (innerhalb festgelegter Grenzen) angegeben. Anhang A oder ISO 26101 2  legt Verfahren für die Feststellung der Eignung der Messumgebung und für die Bestimmung von Korrekturen fest, die durchzuführen sind, um den Einfluss der Messumgebung zu berücksichtigen.
1.4   Messunsicherheit
Es werden Angaben zur Unsicherheit der nach diesem Dokument aus Messungen in Frequenzbändern und mit A-Bewertung bestimmten Schallleistungspegel gemacht. Anhang I legt Verfahren fest, die von Prüflaboratorien angewendet werden können, um Messunsicherheiten zu verringern. Die Unsicherheit entspricht ISO 12001, Genauigkeitsklasse 2. Allgemeine Informationen zur Messunsicherheit sind in diesem Dokument enthalten, und zusätzliche Informationen können ISO 5114 1 entnommen werden.

Acoustique - Détermination des niveaux de puissance et d'énergie acoustiques émis par les sources de bruit à partir de la pression acoustique - Méthodes d'expertise pour des conditions approchant celles du champ libre sur plan réfléchissant (ISO 3744:2025, y compris version corrigée 2026-01)

1.1        Généralités
Le présent document spécifie des méthodes de détermination du niveau de puissance acoustique émis par une source de bruit à partir des niveaux de pression acoustique mesurés sur une surface entourant la source de bruit (machine ou équipement), dans des conditions approchant celles du champ acoustique libre au voisinage d’un ou de plusieurs plans réfléchissants. Le niveau de puissance acoustique produit par la source de bruit, par bandes de fréquences ou avec la pondération A appliquée, est calculé en utilisant ces mesures.
NOTE   Des surfaces de mesure de formes différentes peuvent produire des estimations différentes du niveau de puissance acoustique d’une source de bruit donnée qui sont prises en compte dans l’incertitude associée à cette méthode d’essai. Un code d’essai acoustique rédigé de façon appropriée (voir l’ISO 12001) apporte des informations détaillées sur le choix de la surface.
1.2        Types de bruits et sources de bruit
Les méthodes spécifiées dans le présent document sont applicables à tous les types de bruit (stable, non stable, fluctuant) définis dans l’ISO 12001, à l’exception des événements impulsifs de courte durée.
Le présent document s’applique à tous les types de sources de bruit, quelles que soient leurs dimensions (par exemple composant ou sous-ensemble fixe ou se déplaçant lentement), sous réserve de pouvoir satisfaire les conditions de mesure.
NOTE   Dans le cas de sources particulièrement hautes ou longues (cheminées, conduits, convoyeurs, installations industrielles comprenant plusieurs sources), les conditions de mesure prescrites dans le présent document peuvent s’avérer impraticables. Dans ce cas, un code d’essai acoustique pour la détermination de l’émission sonore d’un type spécifique de sources peut fournir d’autres méthodes.
1.3        Environnement d’essai
Les environnements d’essai qui sont applicables aux mesurages réalisés conformément au présent document peuvent être en salle ou en plein air, comprendre un ou plusieurs plans acoustiques réfléchissants sur lesquels ou à proximité desquels est montée la source de bruit en essai. L’environnement idéal est un espace complètement libre, dépourvu de surfaces limites ou réfléchissantes autres que le ou les plans réfléchissants, tels que ceux d’une salle semi-anéchoïque qualifiée, mais des procédures sont fournies pour appliquer des corrections (dans des limites spécifiées) lorsque ces environnements ne correspondent pas à ces conditions idéales. L’Annexe A ou l’ISO 26101-2 spécifie des méthodes pour déterminer l’adéquation de l’environnement d’essai ainsi que les corrections à appliquer pour tenir compte de l’effet d’environnement.
1.4        Incertitude de mesure
Des informations sont données sur l’incertitude associée aux niveaux de puissance acoustique déterminés conformément au présent document pour des mesurages effectués dans des bandes de fréquences limitées et avec la pondération fréquentielle A. L’Annexe I spécifie les procédures destinées aux laboratoires d’essais qui peuvent être utilisées pour réduire l’incertitude de mesure. L’incertitude est conforme à celle de la classe de précision 2 (classe expertise) définie dans l’ISO 12001. Des informations générales sur l’incertitude de mesure sont fournies dans le présent document et des informations supplémentaires sont disponibles dans l’ISO 5114-1[8].

Akustika - Določanje ravni zvočne moči virov hrupa z uporabo zvočnega tlaka - Inženirske metode za bistveno prosto polje nad odbojno ravnino (ISO 3744:2025, vključno s popravkom 2026-01)

1.1        Splošno
Ta dokument določa metode za določanje ravni zvočne moči vira hrupa iz ravni zvočnega tlaka, izmerjenih na površini, ki obdaja vir hrupa (stroji ali oprema) v okolju, ki približuje akustično prosto polje v bližini ene ali več odbojnih ploskev. Raven zvočne moči, ki jo proizvaja vir hrupa, v frekvenčnih pasovih ali z uporabo A-uteževanja, se izračuna z uporabo teh meritev.
OPOMBA   Različno oblikovane merilne površine lahko dajo različne ocene ravni zvočne moči določenega vira hrupa, kar je upoštevano v negotovosti, povezani s to preskusno metodo. Ustrezno pripravljen kodeks za preskušanje hrupa (glej ISO 12001) daje podrobne informacije o izbiri površine.
1.2        Vrste hrupa in viri hrupa
Metode, določene v tem dokumentu, so primerne za vse vrste hrupa (stalni, nestalni in nihajoči), kot je opredeljeno v ISO 12001, razen za kratkotrajne, impulzne dogodke.
Ta dokument je uporaben za vse vrste in velikosti virov hrupa (npr. stacionarni ali počasi premikajoči se del ali podsklop), pod pogojem, da so pogoji za meritve izpolnjeni.
OPOMBA   Možno je, da so pogoji za meritve, navedeni v tem dokumentu, nepraktični za zelo visoke ali zelo dolge vire, kot so dimniki, kanali, transporterji in industrijski obrati z več viri. Kodeks za preskušanje hrupa za določanje emisij hrupa specifičnih virov lahko v takih primerih zagotovi alternativne metode.
1.3        Preskusno okolje
Preskusna okolja, ki so primerna za meritve v skladu s tem dokumentom, so lahko nameščena v zaprtih prostorih ali na prostem, z eno ali več zvočno odbojnimi ploskvami, na ali blizu katerih je nameščen preskušani vir hrupa. Idealno okolje je popolnoma odprt prostor brez omejujočih ali odbojnih površin, razen odbojnih ploskev, kot ga zagotavlja kvalificirana pol-anekojska komora, vendar so podani postopki za uporabo popravkov (znotraj določenih mej) v primeru okolij, ki so manj kot idealna. Priloga A ali ISO 26101-2 določa metode za določanje ustreznosti preskusnega okolja in za določanje popravkov, ki jih je treba uporabiti za upoštevanje vpliva preskusnega okolja.
1.4        Negotovost meritev
Podane so informacije o negotovosti ravni zvočne moči, določene v skladu s tem dokumentom, za meritve, izvedene v omejenih frekvenčnih pasovih in z uporabo A-uteževanja. Priloga I določa postopke za preskusne laboratorije, ki jih je mogoče uporabiti za zmanjšanje negotovosti meritev. Negotovost je skladna z ISO 12001, natančnostni razred 2 (inženirski razred). Splošne informacije o negotovosti meritev so podane v tem dokumentu, dodatne informacije pa so na voljo v ISO 5114-1[8].

General Information

• Status: Published
• Public Enquiry End Date: 23-Mar-2023
• Publication Date: 14-Jun-2026
• ICS: 17.140.01 - Acoustic measurements and noise abatement in general
• Technical Committee: AKU - Acoustics
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 08-Jun-2026
• Due Date: 13-Aug-2026
• Completion Date: 15-Jun-2026
• Directive: Harmonized Standard2006/42/EC - Directive 2006/42/EC of the European Parliament and of the Council of 17 May 2006 on machinery, and amending Directive 95/16/EC (recast)
• Mandate: M/396 - Mandate to CEN and Cenelec for standardisation in the field of machinery
• Ref Project: EN ISO 3744:2026 - Acoustics - Determination of sound power levels of noise sources using sound pressure - Engineering methods for an essentially free field over a reflecting plane (ISO 3744:2025, including corrected version 2026-01)

Relations

• Replaces: SIST EN 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 3744:2010)
• Effective Date: 01-Jul-2026
• Referred By: SIST EN 17242:2026 - Recirculatory Filtration Fume Cabinets
• Effective Date: 18-Mar-2026
• Referred By: SIST EN 13053:2007+A1:2011 - Ventilation for buildings - Air handling units - Rating and performance for units, components and sections
• Effective Date: 18-Mar-2026
• Referred By: SIST EN 13378:2002 - Pasta processing plants - Pasta presses - Safety and hygiene requirements
• Effective Date: 18-Mar-2026
• Referred By: SIST EN 14673:2007+A1:2010 - Safety of machinery - Safety requirements for hydraulically powered open die hot forging presses for the forging of steel and non-ferrous metals
• Effective Date: 18-Mar-2026
• Referred By: SIST EN 60704-1:2010 - Household and similar electrical appliances - Test code for the determination of airborne noise - Part 1: General requirements (IEC 60704-1:2010)
• Effective Date: 18-Mar-2026
• Referred By: SIST EN 14466:2005+A1:2009 - Fire-fighting pumps - Portable pumps - Safety and performance requirements, tests
• Effective Date: 18-Mar-2026
• Referred By: SIST EN 1886:2008 - Ventilation for buildings - Air handling units - Mechanical performance
• Effective Date: 18-Mar-2026
• Referred By: SIST EN 12733:2018 - Agricultural and forestry machinery - Pedestrian controlled motor mowers - Safety
• Effective Date: 18-Mar-2026
• Referred By: SIST EN 12549:2000+A1:2008 - Acoustics - Noise test code for fastener driving tools - Engineering method
• Effective Date: 18-Mar-2026
• Referred By: SIST EN IEC 63341-3:2026 - Railway applications - Fuel cell systems for rolling stock - Part 3: Performance test methods for fuel cell power systems
• Effective Date: 18-Mar-2026
• Referred By: SIST EN 13732:2013 - Food processing machinery - Bulk milk coolers on farms - Requirements for performance, safety and hygiene
• Effective Date: 18-Mar-2026
• Referred By: SIST EN 71-1:2015 - Safety of toys - Part 1: Mechanical and physical properties
• Effective Date: 18-Mar-2026
• Referred By: SIST EN 13053:2020 - Ventilation for buildings - Air handling units - Rating and performance for units, components and sections
• Effective Date: 18-Mar-2026
• Referred By: SIST EN 13141-8:2014 - Ventilation for buildings - Performance testing of components/products for residential ventilation - Part 8: Performance testing of un-ducted mechanical supply and exhaust ventilation units (including heat recovery) for mechanical ventilation systems intended for a single room
• Effective Date: 18-Mar-2026

Overview

SIST EN ISO 3744:2026 - Acoustics - Determination of sound power levels of noise sources using sound pressure - Engineering methods for an essentially free field over a reflecting plane - specifies standardized engineering methods for determining the sound power level of noise sources (such as machinery or equipment) using sound pressure measurements. This standard is crucial for acoustic measurements where the sound source operates in an environment similar to a free field but includes one or more reflecting planes, commonly representing real-world installation conditions.

The principle behind this standard is to measure sound pressure levels over a surface that envelops the noise source, allowing for an estimate of the total sound energy emitted by the source. The document supports applications in both laboratories and field conditions.

Key Topics

• Sound Power Determination: The standard provides methodologies for quantifying sound power levels using sound pressure measurements around the source, which is vital for noise emission assessment and compliance.
• Measurement Surfaces: Guidelines include different shapes and arrangements for the measurement surface (hemispherical, parallelepiped, cylindrical), each suiting different equipment layouts.
• Types of Noise Covered: The methods apply to various noise types-steady, non-steady, and fluctuating-except for short, impulsive sounds.
• Test Environment: Practical procedures for determining if the acoustic environment (indoors or outdoors) meets criteria for valid results, with corrections available when less-than-ideal conditions are present.
• Measurement Uncertainty: The standard details procedures for estimating and reducing measurement uncertainty, ensuring that results are reliable and repeatable.
• A-weighting and Frequency Bands: Results can be calculated in frequency bands or using A-weighting, aligning with human ear sensitivity and regulatory requirements.

Applications

• Industrial Noise Assessment: SIST EN ISO 3744:2026 is widely used by manufacturers, testing laboratories, and regulatory agencies to assess machinery noise emissions in compliance with product directives and market standards.
• Machinery and Equipment Testing: Suitable for stationary and slowly moving noise sources, the standard assists in evaluating a wide range of industrial components.
• Environmental and Occupational Health: Results support environmental noise control and worker protection programs by ensuring that products meet local and international sound emission requirements.
• Compliance and Declaration: Provides a sound basis for noise emission declarations required in product documentation, procurement, and regulatory submissions.
• Noise Abatement Strategy: Facilitates data-driven noise abatement by accurately identifying main noise sources.

Related Standards

• ISO 3741 to ISO 3747 series: These standards cover various methods for sound power level determination under different acoustic environments and precision grades.
• ISO 12001: Guidance for drafting noise test codes, including measurement surface selection tailored for specific equipment.
• ISO 3745: Sound power measurements in precision environments such as anechoic or hemi-anechoic rooms.
• ISO 6926: Calibration and performance requirements for reference sound sources.
• ISO 26101-1 & ISO/DIS 26101-2: Qualification methods for acoustic environments and environmental corrections.
• IEC 61260, IEC 61672: Instrument specifications on sound level meters and frequency filters.
• ISO/IEC 17025: General requirements for laboratory competence, supporting high-quality, accredited testing.

Practical Value

Implementing SIST EN ISO 3744:2026 ensures accurate, reproducible, and internationally comparable sound power level measurements for noise sources in typical installation conditions. Organizations adopting this standard benefit from:

• Consistency in testing and reporting
• Robust product noise declarations
• Facilitated international market access and regulatory compliance
• Enhanced credibility through standardized procedures
• Support for environmental, health, and safety objectives

This standard is essential for anyone involved in acoustic testing, noise control engineering, or regulatory compliance related to machinery and equipment noise emissions.

Standards Content (Sample)

SLOVENSKI STANDARD
01-julij-2026
Nadomešča:
SIST EN ISO 3744:2010
Akustika - Ugotavljanje ravni moči zvočnih virov hrupa z merjenjem zvočnega
tlaka - Inženirska metoda v pretežno prostem polju nad odbojno ravnino (ISO
3744:2025, vključno s popravljeno različico 2026-01)
Acoustics - Determination of sound power levels of noise sources using sound pressure -
Engineering methods for an essentially free field over a reflecting plane (ISO 3744:2025,
including corrected version 2026-01)
Akustik - Bestimmung der Schallleistungs- und Schallenergiepegel von Geräuschquellen
aus Schalldruckmessungen - Hüllflächenverfahren der Genauigkeitsklasse 2 für ein im
Wesentlichen freies Schallfeld über einer reflektierenden Ebene (ISO 3744:2025,
korrigierte Fassung 2026-01)
Acoustique - Détermination des niveaux de puissance et d'énergie acoustiques émis par
les sources de bruit à partir de la pression acoustique - Méthodes d'expertise pour des
conditions approchant celles du champ libre sur plan réfléchissant (ISO 3744:2025, y
compris version corrigée 2026-01)
Ta slovenski standard je istoveten z: EN ISO 3744:2026
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 3744
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2026
EUROPÄISCHE NORM
ICS 17.140.01 Supersedes EN ISO 3744:2010
English Version
Acoustics - Determination of sound power levels of noise
sources using sound pressure - Engineering methods for
an essentially free field over a reflecting plane (ISO
3744:2025, including corrected version 2026-01)
Acoustique - Détermination des niveaux de puissance Akustik - Bestimmung der Schallleistungspegel von
acoustique et des niveaux d'énergie acoustique émis Geräuschquellen aus Schalldruckmessungen -
par les sources de bruit à partir de la pression Hüllflächenverfahren der Genauigkeitsklasse 2 für ein
acoustique - Méthodes d'expertise pour des conditions im Wesentlichen freies Schallfeld über einer
approchant celles du champ libre sur plan réfléchissant reflektierenden Ebene (ISO 3744:2025, korrigierte
(ISO 3744:2025, y compris version corrigée 2026-01) Fassung 2026-01)
This European Standard was approved by CEN on 13 October 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
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
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
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 3744:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
Annex ZA (informative) Relationship between this European Standard and the essential
requirements of Directive 2006/42/EC aimed to be covered . 4

European foreword
This document (EN ISO 3744:2026) 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 September 2026, and conflicting national standards
shall be withdrawn at the latest by September 2026.
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.
This document supersedes EN ISO 3744:2010.
This document has been prepared under a standardization request addressed to CEN by the European
Commission. The Standing Committee of the EFTA States subsequently approves these requests for its
Member States.
For the relationship with EU Legislation, see informative Annex ZA, which is an integral part of this
document.
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 3744:2025, including corrected version 2026-01 has been approved by CEN as
Annex ZA
(informative)
Relationship between this European Standard and the essential
requirements of Directive 2006/42/EC aimed to be covered
This European Standard has been prepared under a Commission’s standardization request “M/396
Mandate CEN and CENELEC for Standardisation in the field of machinery" to provide one voluntary
means of conforming to essential requirements of Directive 2006/42/EC of the European Parliament
and of the Council of 17 May 2006 on machinery, and amending Directive 95/16/EC (recast)
Once this standard is cited in the Official Journal of the European Union under that Directive,
compliance with the normative clauses of this standard given in Table ZA.1 confers, within the limits of
the scope of this standard, a presumption of conformity with the corresponding essential requirements
of that Directive, and associated EFTA regulations.
Table ZA.1 — Correspondence between this European Standard and Annex I of Directive
2006/42/EC
The relevant Essential Clause(s)/sub-clause(s) of this Remarks/Notes
Requirements of Directive EN
2006/42/EC
1.5.8 Noise 3, 4, 5, 6, 7, 8, 9, 10, 11, The sound power level,
Annexes A, B, C, D, E, F, G, H, I determined according to this
1.7.4.2 u) and 1.7.4.3
document, is one of two
quantities needed to address
EHSR 1.5.8 about noise
reduction at design stage,
EHSR 1.7.4.2 u) and EHSR 1.7.4.3
which, in turn, support the "Sell
& Buy Quiet" strategy.
Table ZA.2 — Applicable standards to confer presumption of conformity as described in this
Annex ZA
Column 1 Column 2 Column 3 Column 4
Reference in International Title Corresponding
Clause 2 Standard edition European Standard
edition
ISO 6926 ISO 6926:2016 Acoustics — Requirements EN ISO 6926:2016
for the performance and
calibration of reference
sound sources used for the
determination of sound
power levels
ISO 26101-1 ISO 26101-1:2021 Acoustics — Test methods EN ISO 26101-1:2022
for the qualification of the
acoustic environment —
Part 1: Qualification of free-
Column 1 Column 2 Column 3 Column 4
Reference in International Title Corresponding
Clause 2 Standard edition European Standard
edition
field environments
ISO 26101-2 ISO 26101-2:2024 Acoustics — Test methods EN ISO 26101-2:2024
for the qualification of the
acoustic environment—
Part 2: Determination of
the environmental
correction
ISO 12001 ISO 12001:1996 Acoustics — Noise emitted EN ISO 12001:2009
by machinery and
equipment — Rules for the
drafting and presentation
of a noise test code
IEC 61260-3 IEC 61260-3:2016 Electroacoustics – Octave- EN 61260-3:2016
band and fractional-octave-
band filters – Part 3:
Periodic tests
IEC 61260-2 IEC 61260-2:2016 Electroacoustics - Octave- EN 61260-2:2016
band and fractional-octave-
band filters - Part 2:
Pattern-evaluation tests
IEC 61672-1 IEC 61672-1:2013 Electroacoustics — Sound EN 61672-1:2013
level meters — Part 1:
Specifications
IEC 61672-3 IEC 61672-3:2013 Electroacoustics - Sound EN 61672-3:2013
level meters - Part 3:
Periodic tests
ISO/IEC 17025 ISO/IEC 17025:2017 General requirements for EN ISO/IEC
the competence of testing 17025:2017
and calibration laboratories
The documents listed in the Column 1 of Table ZA.2, in whole or in part, are normatively referenced in
this document, i.e. are indispensable for its application. The achievement of the presumption of
conformity is subject to the application of the edition of Standards as listed in Column 4 or, if no
European Standard Edition exists, the International Standard Edition given in Column 2 of Table ZA.2.
WARNING 1 Presumption of conformity stays valid only as long as a reference to this European
Standard is maintained in the list published in the Official Journal of the European Union. Users of this
standard should consult frequently the latest list published in the Official Journal of the European
Union.
WARNING 2 Other Union legislation may be applicable to the product(s) falling within the scope of
this standard.
International
Standard
ISO 3744
Fourth edition
Acoustics — Determination of
2025-12
sound power levels of noise
sources using sound pressure
Corrected version
— Engineering methods for
2026-01
an essentially free field over a
reflecting plane
Acoustique — Détermination des niveaux de puissance
acoustique et des niveaux d’énergie acoustique émis par les
sources de bruit à partir de la pression acoustique — Méthodes
d’expertise pour des conditions approchant celles du champ libre
sur plan réfléchissant
Reference number
ISO 3744:2025(en) © ISO 2025
ISO 3744:2025(en)
© ISO 2025
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
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.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
ISO 3744:2025(en)
Contents Page
Foreword .v
Introduction .vii
1 Scope . 1
1.1 General .1
1.2 Types of noise and noise sources .1
1.3 Test environment .1
1.4 Measurement uncertainty .1
2 Normative references . 2
3 Terms and definitions . 2
4 Test environment . 5
4.1 General .5
4.2 Criterion for acoustic adequacy of test environment .6
4.3 Criterion for environmental correction .7
4.4 Criteria for background noise .7
4.4.1 General .7
4.4.2 Relative background noise criteria for A-weighted measurements .7
4.4.3 Background noise conformity for determination of conformity with criteria .8
5 Instrumentation . 8
5.1 General .8
5.2 Operational check .8
5.3 Verification . .8
6 Definition, location, installation, and operation of noise source under test . 9
6.1 General .9
6.2 Auxiliary equipment .9
6.3 Noise source location .9
6.4 Mounting of the noise source . .10
6.4.1 General .10
6.4.2 Hand-held machinery and equipment .10
6.4.3 Base-mounted, wall-mounted, and tabletop machinery and equipment .10
6.5 Installation and mounting conditions for moving noise sources .10
6.6 Operation of source during test .10
7 Reference box and measurement surface .11
7.1 Reference box.11
7.2 Measurement surface . 12
7.2.1 General . 12
7.2.2 Microphone orientation . 12
7.2.3 Hemispherical measurement surface . 13
7.2.4 Parallelepiped measurement surface . 13
7.2.5 Cylindrical measurement surface .14
7.2.6 Combination measurement surface . 15
8 Determination of sound power levels .15
8.1 Microphone positions on the measurement surface. 15
8.1.1 Hemispherical measurement surface . 15
8.1.2 Parallelepiped measurement surface .16
8.1.3 Cylindrical measurement surface .17
8.1.4 Combination measurement surface .17
8.2 Determination of sound power levels .17
8.2.1 Measurement of sound pressure levels .17
8.2.2 Calculation of mean sound pressure levels .17
8.2.3 Corrections for background noise .18
8.2.4 Calculation of surface sound pressure levels .18
8.2.5 Calculation of sound power levels .19

iii
ISO 3744:2025(en)
9 Measurement uncertainty . 19
9.1 Methodology .19
9.2 Typical values of σ . 20
R0
9.3 Determination of σ . 20
omc
9.4 Total standard deviation σ and expanded measurement uncertainty, U . 20
tot
10 Information to be recorded .21
10.1 General .21
10.2 Noise source under test .21
10.3 Test environment .21
10.4 Instrumentation . 22
10.5 Acoustical data . 22
11 Test report .22
Annex A (normative) Qualification procedures for the acoustic environment and measurement
surface . .23
Annex B (normative) Microphone arrays on a hemispherical measurement surface .25
Annex C (normative) Microphone arrays on a parallelepiped measurement surface .33
Annex D (normative) Microphone arrays on a cylindrical measurement surface .45
Annex E (normative) Measurement surface with segments having unequal areas .50
Annex F (normative) Alternative microphone array on a hemispherical measurement surface
for direct measurements of A-weighted sound pressure levels .51
Annex G (normative) Calculation of A-weighted sound power levels from frequency band levels .54
Annex H (normative) Sound power levels under reference meteorological conditions .56
Annex I (informative) Laboratory procedures for reduction of uncertainties associated with
sound power level determinations .58
Bibliography .60

iv
ISO 3744:2025(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).
This fourth edition of ISO 3744 cancels and replaces the third edition (ISO 3744:2010), which has been
technically revised.
The main changes are as follows:
— removed sound energy level determination due to lack of use and because it was highly duplicative of
other text in the method,
— moved many of the special case measurement conditions and measurement parameters into Annexes to
simplify the main body of the standard to focus on the basic sound power level determination method for
typical sources and test environments,
— removed absolute background noise criteria and replaced with new criteria for conformity with
background noise requirements,
— removed the estimation methods for K from an estimation of the equivalent sound absorption area,
— instrumentation requirements revised to accommodate modern modular computerized instrumentation
systems,
— requirements for the cylinder were updated to be consistent with ISO 7779,
— qualification methods for the test environment, other than the absolute comparison test, removed and
moved to ISO 26101-2,
— new Annex I specifies procedures that testing laboratories can apply to reduce measurement uncertainties
associated with the test method,
— measurements using a cylindrical measurement surface were clarified.

v
ISO 3744:2025(en)
This revision does not change the basic measurement procedure for sound power level determination as
specified in the 2010 version of this document. The standard deviation of reproducibility for measurements
conducted in accordance with the main body of this revision remains the same as in the 2010 version.
Measurements conducted in accordance with the 2010 version are expected to be equivalent to those
obtained using this revision, unless the ISO 3744:2010 measurements were conducted in a test environment
that was qualified using a K that was calculated from an estimation of the equivalent sound absorption
area, since this way to determine K was removed from this revision of the document.
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.
This corrected version of ISO 3744:2025 incorporates the following corrections:
— Correction of formulae in Figures C.3 and C.4.

vi
ISO 3744:2025(en)
Introduction
[2]to[6]
This document is one of the series ISO 3741 to ISO 3747 which specify various methods for determining
the sound power levels of noise sources including machinery, equipment and their sub-assemblies. General
[1]
guidelines to assist in the selection are provided in ISO 3740 . The selection depends on the available
test environment and on the precision of the sound power level values required. A noise test code can
be established (see ISO 12001) for the individual noise source in order to select the appropriate sound
[2]
measurement surface and microphone array from among those allowed in each member of the ISO 3741
[6]
to ISO 3747 series, and to give requirements on test unit mounting, loading and operating conditions
under which the sound power levels are to be obtained. The sound power emitted by a given source into the
test environment is calculated from the mean square sound pressure that is measured over a hypothetical
measurement surface enclosing the source, and the area of that surface.
The methods specified in this document permit the determination of the A-weighted sound power level and
optionally the sound power level in octave or 1/3-octave frequency bands.
The main body of this document specifies test environment qualification criteria, testing procedures
and the associated measurement uncertainties for basic compliance with the method. Annex I specifies
additional requirements that may be applied by testing laboratories to reduce measurement uncertainty.
[2]
For applications where even greater accuracy is required, reference can be made to ISO 3745, ISO 3741 or
[9][10][11]
ISO 9614 . If the relevant criteria for the measurement environment specified in this document are
[9][10][11]
not met, it might be possible to refer to another standard from this series, or to ISO 9614 .
This document specifies methods of accuracy grade 2 (engineering grade) as defined in ISO 12001, when the
measurements are performed in a space that approximates an acoustically free field over a reflecting plane.
Such an environment can be found in a specially designed room, or within industrial buildings or outdoors.
Ideally, the test source should be mounted on a sound-reflecting plane located in a large open space. For
sources normally installed on the floor of machine rooms, corrections are specified to account for undesired
reflections from nearby objects, walls and ceiling, and for background noises.
This test method was originally issued as ISO 4872 in 1978. It was first released as ISO 3744 in 1994. A brief
history of the technical requirements associated with the revisions of this test method follows.
ISO 3744:1994 required a test environment with a K 2dB in all frequency bands of interest and required
2f
measurements to be conducted in octave or one-third octave bands, with A-weighted levels being calculated
from the band level data over the frequency range of interest.
ISO 3744:2010 relaxed the requirements on the test environment to require K 4dB and allowed
2A
A-weighted levels to be determined either by calculation from frequency band level measurements or by
direct measurement using an A-weighted filter. These changes to the requirements for the test environment
and instrumentation were made to facilitate in-situ and field sound power level determinations using
equipment without proportional octave band filtering for evaluation of compliance with regulatory
requirements. Round robin studies were conducted to verify that the stated measurement uncertainties
[18]
associated with the method could be maintained using these requirements .
In addition, the 2010 revision added methods for sound energy level determination of short duration
transient events, several special case sound power level determination conditions to the main body of the
standard and several new measurement parameters.

vii
International Standard ISO 3744:2025(en)
Acoustics — Determination of sound power levels of noise
sources using sound pressure — Engineering methods for an
essentially free field over a reflecting plane
1 Scope
1.1 General
This document specifies methods for determining the sound power level of a noise source from sound
pressure levels measured on a surface enveloping the noise source (machinery or equipment) in an
environment that approximates to an acoustic free field near one or more reflecting planes. The sound
power level produced by the noise source, in frequency bands or with A-weighting applied, is calculated
using those measurements.
NOTE Differently shaped measurement surfaces can yield differing estimates of the sound power level of a given
noise source which are accounted for in the uncertainty associated with this test method. An appropriately drafted
noise test code (see ISO 12001) gives detailed information on the selection of the surface.
1.2 Types of noise and noise sources
The methods specified in this document are suitable for all types of noise (steady, non-steady, and
fluctuating) as defined in ISO 12001, except for short duration, impulsive events.
This document is applicable to all types and sizes of noise source (e.g. stationary or slowly moving component
or sub-assembly), provided that the conditions for the measurements can be met.
NOTE It is possible that the conditions for measurements given in this document are impracticable for very tall
or very long sources such as chimneys, ducts, conveyors and multi-source industrial plants. A noise test code for the
determination of noise emission of specific sources can provide alternative methods in such cases.
1.3 Test environment
The test environments that are applicable for measurements made in accordance with this document can
be located indoors or outdoors, with one or more sound-reflecting planes present on or near which the
noise source under test is mounted. The ideal environment is a completely open space with no bounding
or reflecting surfaces other than the reflecting plane(s), such as that provided by a qualified hemi-anechoic
chamber, but procedures are given for applying corrections (within limits that are specified) in the case
of environments that are less than ideal. Annex A or ISO 26101-2 specifies methods for determining the
adequacy of the test environment and for determination of corrections to be applied to account for the effect
of the test environment.
1.4 Measurement uncertainty
Information is given on the uncertainty of the sound power levels determined in accordance with this
document, for measurements made in limited bands of frequency and with frequency A-weighting applied.
Annex I specifies procedures for testing laboratories that can be used to reduce measurement uncertainty.
The uncertainty conforms to ISO 12001, accuracy grade 2 (engineering grade). General information
on measurement uncertainty is provided in this document and additional information can be found in
[8]
ISO 5114-1 .
ISO 3744:2025(en)
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 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
ISO 26101-2:2024, Acoustics — Test methods for the qualification of the acoustic environment— Part 2:
Determination of the environmental correction
ISO 12001, Acoustics — Noise emitted by machinery and equipment — Rules for the drafting and presentation
of a noise test code
IEC 60942:2017, Electroacoustics — Sound calibrators
IEC 61260-1:2014, Electroacoustics — Octave-band and fractional-octave-band filters — Part 1: Specifications
IEC 61260-2, Electroacoustics — Octave-band and fractional-octave-band filters — Part 2: Pattern-evaluation
tests
IEC 61260-3, Electroacoustics — Octave-band and fractional-octave-band filters — Part 3: Periodic tests
IEC 61672-1, Electroacoustics — Sound level meters — Part 1: Specifications
IEC 61672-3, Electroacoustics — Sound level meters — Part 3: Periodic tests
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology 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/
3.1
sound pressure
p
difference between instantaneous total pressure and static pressure
Note 1 to entry: Sound pressure is expressed in pascals.
[13]
[SOURCE: ISO 80000-8:2020 , 8-2.2, modified — Note 1 to entry added.]
3.2
sound pressure level
L
p
ISO 3744:2025(en)
quantity given by:
p
rms
L 10lg dB
p
p
where p is the root-mean-square sound pressure (3.1) in the time domain and p is the reference value for
rms 0
sound pressure (3.1)
t
p  ptdt
rms

T
t
and p 20Pa is the reference value of sound pressure (3.1)
Note 1 to entry: If specific frequency and time weightings as specified in IEC 61672-1 and/or specific frequency bands
are applied, this is indicated by appropriate subscripts; e.g. L denotes the A-weighted sound pressure level.
pA
[13]
[SOURCE: ISO 80000-8:2020 , 8-14, modified — Deleted remarks and added instead Note 1 to entry and
Note 2 to entry.]
3.3
measurement time interval
T
portion or a multiple of an operational period or operational cycle of the noise source under test for which
the sound pressure level (3.2) is determined
Note 1 to entry: Measurement time interval is expressed in seconds.
3.4
acoustic free field
sound field in a homogeneous, isotropic medium free of boundaries
Note 1 to entry: In practice, an acoustic free field is a field in which the influence of reflections at the boundaries or
other disturbing objects is negligible over the frequency range of interest.
3.5
acoustic free field over a reflecting plane
essentially acoustic free field (3.4) over a reflecting plane in the absence of any other obstacles
3.6
reflecting plane
sound reflecting planar surface on which the noise source under test is located
3.7
frequency range of interest
frequency range of octave bands with nominal mid-band frequencies from 125 Hz to
8 000 Hz (including one-third octave bands with mid-band frequencies from 100 Hz to 10 000 Hz)
Note 1 to entry: For special purposes, the frequency range may be extended or reduced, provided that the test
environment and instrument specifications are satisfactory for use over the modified frequency range. Changes to the
frequency range of interest shall be included in the test report.
3.8
reference box
hypothetical right parallelepiped terminating on the reflecting plane(s) (3.6) on which the noise source under
test is located, that just encloses the source including all the significant sound radiating components and any
test table on which the source is mounted
Note 1 to entry: If required, the smallest possible test table may be used for compatibility with emission sound
[12]
pressure measurements at bystander positions in accordance with, for example, ISO 11201 .

ISO 3744:2025(en)
3.9
characteristic source dimension
d
distance from the origin of the coordinate system to the farthest corner of the reference box (3.8)
Note 1 to entry: Characteristic source dimension is expressed in metres.
3.10
measurement distance
d
distance from the reference box (3.8) to a parallelepiped measurement surface or to a cylindrical
measurement surface
Note 1 to entry: Measurement distance is expressed in metres.
3.11
measurement radius
r
radius of a hemispherical measurement surface or a cylindrical measurement surface
Note 1 to entry: Measurement radius is expressed in metres.
3.12
measurement surface
hypothetical surface of area, S, on which the microphone positions are located at which the sound pressure
levels (3.2) are measured, enveloping the noise source under test and terminating on the reflecting plane(s)
(3.6) on which the sou
...