SIST EN ISO 3744:2026
(Main)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)
- Abstract
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].
- Status
- Published
- Public Enquiry End Date
- 23-Mar-2023
- Publication Date
- 14-Jun-2026
- 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
- 2006/42/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)OJ Ref: L 7.9.2026 OJ Date: 07-Sep-2026
SIST EN ISO 3744:2026 is the Slovenian standard published by SIST as the national adoption of EN ISO 3744:2026, reproducing ISO 3744:2025 including the corrected version 2026-01. It specifies engineering methods for determining sound power levels of machinery and equipment from sound pressure measurements on an enveloping surface in an environment that approximates an acoustic free field over a reflecting plane. It is used by test laboratories, manufacturers, and others who need engineering-grade noise emission results for declaration, verification, or product development.
What does SIST EN ISO 3744:2026 specify?
SIST EN ISO 3744:2026 specifies how to determine the sound power level of a noise source from sound pressure levels measured on a surface surrounding the source. The method applies to sources mounted near one or more reflecting planes, indoors or outdoors, and gives results in frequency bands or as A-weighted values.
The document covers steady, non-steady, and fluctuating noise, but not short duration impulsive events. It is intended for all types and sizes of noise source, including machinery, equipment, and sub-assemblies, provided the measurement conditions can be met.
The document is organized into main clauses on scope, references, terms, test environment, instrumentation, source installation and operation, reference boxes and measurement surfaces, sound power calculation, uncertainty, records, and the test report. It also includes nine annexes, several of them normative.
| Annex | What it covers |
|---|---|
| Annex A | Qualification procedures for the acoustic environment and measurement surface |
| Annex B | Microphone arrays on a hemispherical measurement surface |
| Annex C | Microphone arrays on a parallelepiped measurement surface |
| Annex D | Microphone arrays on a cylindrical measurement surface |
| Annex E | Measurement surfaces with unequal segment areas |
| Annex F | Alternative hemispherical array for direct A-weighted measurements |
| Annex G | Calculation of A-weighted sound power levels from frequency band levels |
| Annex H | Sound power levels under reference meteorological conditions |
| Annex I | Laboratory procedures to reduce uncertainty |
What are the key requirements of SIST EN ISO 3744:2026?
SIST EN ISO 3744:2026 is built around a simple sequence: qualify the test environment, set up the source in a defined way, measure sound pressure on a prescribed surface, apply the required corrections, and report the resulting sound power level with uncertainty. In practice, the standard tells you what environment is acceptable, how to arrange microphones, and what to record so the result can be repeated.
Test environment and background noise
SIST EN ISO 3744:2026 requires a test environment that is close to an acoustic free field over a reflecting plane. The ideal case is a fully open space or a qualified hemi-anechoic chamber, but the standard also allows corrections when the environment is not ideal, provided the environmental correction stays within the limit for use of the method.
This matters because room reflections can bias the result. The document therefore separates the qualification of the environment from the measurement itself, and it points users to Annex A or ISO 26101-2 for determining the environmental correction.
Instrumentation and checks
SIST EN ISO 3744:2026 requires class 1 sound level measurement equipment for the relevant parameters, class 1 filters, and a class 1 sound calibrator. The beginning and end of each measurement session shall be checked, and the difference between two consecutive checks shall be within 0.5 dB.
This matters in practice because unstable instrumentation can invalidate a test day. The document also requires verification of the measuring system, filters, and calibrator through valid conformity evidence and conformance testing in an ISO/IEC 17025 laboratory.
Source installation and operation
SIST EN ISO 3744:2026 requires the noise source to be installed and operated as it would be in normal use, while following any applicable noise test code. Auxiliary equipment, piping, ducts, and connections must not add significant sound of their own, and the source under test must include any auxiliary equipment that cannot be removed or adequately quietened.
This is important because setup choices can change the measured sound power. For moving sources, the source traverses a defined straight path. For all sources, the operating mode should be reproducible and representative of the noisiest typical use, such as full load, idling, maximum speed, or a defined work cycle.
Reference box and measurement surfaces
SIST EN ISO 3744:2026 first defines a reference box that just encloses the source, then uses that box to choose the measurement surface. The permitted measurement surfaces are hemispherical, parallelepiped, cylindrical, and combination surfaces.
This matters because the surface shape changes the measurement geometry and the uncertainty. The standard uses the characteristic source dimension, measurement distance, and measurement radius to place microphones or traverses. Annexes B, C, and D provide the arrays for the main surface types, and Annex F provides an alternative hemispherical array for direct A-weighted measurements.
Sound power calculation and corrections
SIST EN ISO 3744:2026 calculates sound power from the mean sound pressure level over the measurement surface, with corrections for background noise and the test environment. If the measurement surface has unequal segment areas, Annex E gives the averaging method. If results are reported in bands, Annex G gives the calculation of A-weighted sound power from band data.
This matters because the standard is not just a measurement layout - it defines how to turn measured pressures into a final sound power level. Annex H gives the adjustment to reference meteorological conditions, which is relevant at higher altitudes and in low-temperature conditions.
Uncertainty, records, and report
SIST EN ISO 3744:2026 treats uncertainty as part of the result. It uses the total standard deviation and expanded measurement uncertainty, with typical values given for engineering-grade work, and Annex I offers a laboratory route to lower uncertainty.
The standard also requires recording the source, test environment, instrumentation, acoustical data, and corrections, then reporting enough detail to reproduce the test. If the result is fully in conformity, the report may say so; if not, it must not imply full conformity.
What terms does SIST EN ISO 3744:2026 define?
- Sound pressure - the difference between instantaneous total pressure and static pressure, expressed in pascals.
- Sound pressure level - the logarithmic level derived from root-mean-square sound pressure relative to 20 µPa.
- Reference box - the smallest right parallelepiped that just encloses the source, including significant radiating parts and any test table.
- Characteristic source dimension, d - the distance from the coordinate origin to the farthest corner of the reference box.
- Measurement surface - the hypothetical surface on which microphone positions are located around the source for sound pressure measurement.
- Background noise correction, K - the correction applied to account for noise from other sources and instrumentation.
- Environmental correction, K - the correction applied to account for reflected or absorbed sound from the test environment.
- Noise test code - a source-specific standard that gives the information needed to carry out noise emission measurements under standardized conditions.
Who uses SIST EN ISO 3744:2026?
SIST EN ISO 3744:2026 is used by manufacturers of machinery and equipment, acoustic test laboratories, quality and compliance teams, and engineers who need sound power data for product design or comparison. It is also relevant to buyers and specifiers who rely on declared noise emission values.
The standard is especially relevant where noise emission has to be measured in a controlled engineering way, rather than by a quick survey method. The European foreword also links it to the machinery directive context, so it is used in work connected with noise-related essential requirements for machinery.
What changed in SIST EN ISO 3744:2026 from the previous edition?
SIST EN ISO 3744:2026 supersedes EN ISO 3744:2010 and reflects the fourth edition of ISO 3744.
The changes stated in the document include:
- removal of sound energy level determination
- movement of many special-case conditions and parameters into annexes
- replacement of absolute background noise criteria with background noise conformity criteria
- removal of methods for estimating K from equivalent sound absorption area
- revised instrumentation requirements for modern modular computerized systems
- updated cylinder requirements aligned with ISO 7779
- transfer of some test-environment qualification methods to ISO 26101-2
- new Annex I procedures to reduce measurement uncertainty
- clarification of cylindrical measurement-surface measurements
- correction of formulae in Figures C.3 and C.4 in the corrected version
The document also states that the basic measurement procedure and reproducibility for the main method remain unchanged from the 2010 version.
Which standards are used with SIST EN ISO 3744:2026?
SIST EN ISO 3744:2026 relies on several normative references and companion standards:
- ISO 3745 - used for precision methods and for qualifying hemi-anechoic environments
- ISO 6926 - used for performance and calibration of reference sound sources
- ISO 26101-1 - used for qualification of free-field environments
- ISO 26101-2 - used for environmental correction and qualification methods
- ISO 12001 - used for noise test codes and general noise-emission measurement rules
- IEC 60942 - used for sound calibrators
- IEC 61260-1, IEC 61260-2, IEC 61260-3 - used for octave-band and fractional-octave-band filters
- IEC 61672-1, IEC 61672-3 - used for sound level meters and their periodic tests
- ISO/IEC 17025 - used for laboratory competence
- ISO 5114-1 - gives additional guidance on uncertainty associated with sound power measurements from sound pressure data
The document also points to the ISO 3740 to ISO 3747 series and to ISO 9614-1, ISO 9614-2, and ISO 9614-3 when different methods or higher accuracy are needed.
What does the SIST EN ISO 3744:2026 document contain?
SIST EN ISO 3744:2026 contains detailed measurement surfaces, microphone arrays, and calculation procedures for hemispherical, parallelepiped, cylindrical, and combination arrangements. The annexes provide tables and figures that define microphone coordinates, traversing paths, and how to treat unequal surface areas.
It also includes the procedure for the absolute comparison test, the calculation of A-weighted sound power from frequency bands, and the adjustment to reference meteorological conditions. These parts are used for test development, laboratory setup, compliance testing, and the preparation of reproducible noise reports.
Relations
- Effective Date
- 01-Jul-2026
- Effective Date
- 18-Mar-2026
- 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
- Effective Date
- 18-Mar-2026
- Effective Date
- 18-Mar-2026
- Effective Date
- 18-Mar-2026
- Referred By
SIST EN 1886:2008 - Ventilation for buildings - Air handling units - Mechanical performance - Effective Date
- 18-Mar-2026
- Effective Date
- 18-Mar-2026
- Effective Date
- 18-Mar-2026
- Effective Date
- 18-Mar-2026
- Effective Date
- 18-Mar-2026
- Effective Date
- 18-Mar-2026
- Effective Date
- 18-Mar-2026
- Effective Date
- 18-Mar-2026
Get Certified
Connect with accredited certification bodies for this standard
BSMI (Bureau of Standards, Metrology and Inspection)
Taiwan's standards and inspection authority.
Sponsored listings
Frequently Asked Questions
SIST EN ISO 3744:2026 is a standard published by the Slovenian Institute for Standardization (SIST). Its full title is "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)". This standard covers: 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].
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].
SIST EN ISO 3744:2026 is classified under the following ICS (International Classification for Standards) categories: 17.140.01 - Acoustic measurements and noise abatement in general. The ICS classification helps identify the subject area and facilitates finding related standards.
SIST EN ISO 3744:2026 has the following relationships with other standards: It is inter standard links to SIST EN ISO 3744:2010, SIST EN 17242:2026, SIST EN 13053:2007+A1:2011, SIST EN 13378:2002, SIST EN 14673:2007+A1:2010, SIST EN 60704-1:2010, SIST EN 14466:2005+A1:2009, SIST EN 1886:2008, SIST EN 12733:2018, SIST EN 12549:2000+A1:2008, SIST EN IEC 63341-3:2026, SIST EN 13732:2013, SIST EN 71-1:2015, SIST EN 13053:2020, SIST EN 13141-8:2014. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
SIST EN ISO 3744:2026 is associated with the following European legislation: EU Directives/Regulations: 2006/42/EC; Standardization Mandates: M/396. When a standard is cited in the Official Journal of the European Union, products manufactured in conformity with it benefit from a presumption of conformity with the essential requirements of the corresponding EU directive or regulation.
SIST EN ISO 3744:2026 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
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: +41 22 749 01 11
Email: copyright@iso.org
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 10 lg 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 pt dt
rms
T
t
and p 20 Pa 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
...