FprEN ISO 3744

SLOVENSKI STANDARD
oSIST prEN ISO 3744:2023
01-marec-2023
Akustika - Ugotavljanje ravni zvočnih moči virov hrupa z merjenjem zvočnega
tlaka - Inženirska metoda v pretežno prostem polju nad odbojno ravnino (ISO/DIS
3744:2023)
Acoustics - Determination of sound power levels of noise sources using sound pressure -
Engineering methods for an essentially free field over a reflecting plane (ISO/DIS
3744:2023)
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/DIS 3744:2023)
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/DIS 3744:2023)
Ta slovenski standard je istoveten z: prEN ISO 3744
ICS:
17.140.01 Akustična merjenja in Acoustic measurements and
blaženje hrupa na splošno noise abatement in general
oSIST prEN ISO 3744:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN ISO 3744:2023
oSIST prEN ISO 3744:2023
DRAFT INTERNATIONAL STANDARD
ISO/DIS 3744
ISO/TC 43/SC 1 Secretariat: DIN
Voting begins on: Voting terminates on:
2023-01-06 2023-03-31
Acoustics — Determination of sound power levels of noise
sources using sound pressure — Engineering methods for
an essentially free field over a reflecting plane
ICS: 17.140.01
This document is circulated as received from the committee secretariat.
THIS DOCUMENT IS A DRAFT CIRCULATED
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oSIST prEN ISO 3744:2023
ISO/DIS 3744:2023(E)
DRAFT INTERNATIONAL STANDARD
ISO/DIS 3744
ISO/TC 43/SC 1 Secretariat: DIN
Voting begins on: Voting terminates on:

Acoustics — Determination of sound power levels of noise
sources using sound pressure — Engineering methods for
an essentially free field over a reflecting plane
ICS: 17.140.01
This document is circulated as received from the committee secretariat.
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FOR COMMENT AND APPROVAL. IT IS
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PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022

oSIST prEN ISO 3744:2023
ISO/DIS 3744:2022(E)
Contents Page
Foreword .v
Introduction . vi
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 . 6
4.1 General . 6
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 . 8
4.4.3 Background Noise Compliance for Determination of Compliance with a
Criteria . 8
5 Instrumentation . 8
5.1 General . 8
5.2 Operational Check . 8
5.3 Verification . . 9
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 . 10
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 . 11
6.5 Installation and mounting conditions for moving noise sources . 11
6.6 Operation of source during test . 11
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 . 13
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
iii
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8.2.4 Calculation of surface sound pressure levels . 18
8.2.5 Calculation of sound power levels . 19
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 σσ 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 . 21
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 (normative) Laboratory Procedures for Reduction of Uncertainties Associated
with Sound Power Level Determinations .58
Annex ZA (informative) Relationship between this European Standard and the essential
requirements of Directive 2006/42/EC aimed to be covered .60
Bibliography .61
iv
oSIST prEN ISO 3744:2023
ISO/DIS 3744:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation 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.
This fourth edition of ISO 3744 constitutes a merger and a technical revision of and cancels and replaces
the third edition (ISO 3744:2010), second edition (ISO 3744:1994) and the first edition of this test
method which was issued as ISO 4872:1978.
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.
v
oSIST prEN ISO 3744:2023
ISO/DIS 3744:2022(E)
Introduction
[2-6]
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-
[1]
assemblies. General 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 measurement surface and microphone array from among those allowed
[2] [6]
in each member of the ISO 3741 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 defines test environment qualification criteria, testing procedures
and the associated measurement uncertainties for basic compliance with the method. Annex I
outlines additional requirements that may be applied by testing laboratories to reduce measurement
uncertainty. For applications where even greater accuracy is required, reference can be made to
[2] [13,14,15]
ISO 3745, ISO 3741 or ISO 9614. If the relevant criteria for the measurement environment
specified in this document are not met, it might be possible to refer to another standard from this
[13,14,15]
series, or to ISO 9614 .
This document describes 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
defined 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
2f
required 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 associated with the method could be maintained using these
[26]
requirements .
In addition, the 2010 revision added methods for sound energy level determination of short duration
transient events, a number of special case sound power level determination conditions to the main
body of the standard and several new measurement parameters.
This revision of ISO 3744 removes sound energy level determination due to lack of use and because it
was highly duplicative of other text in the method. Those users with an interest in sound energy level
can continue to refer to ISO 3744:2010 until this working group develops an independent test method
on sound energy level determination. Also, this revision moves 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.
vi
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ISO/DIS 3744:2022(E)
In addition, a new Annex I outlines procedures that testing laboratories may apply to reduce
measurement uncertainties associated with the test method.
vii
oSIST prEN ISO 3744:2023
oSIST prEN ISO 3744:2023
DRAFT INTERNATIONAL STANDARD ISO/DIS 3744:2022(E)
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, or a noise
test code that refers to this 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 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
1)
specified) in the case of environments that are less than ideal. Annex A or ISO/DIS 26101-2:— defines
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 outlines 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
2)
be found in ISO/DIS 5114-1:— .
1) Under preparation Stage at the time of the ballot: ISO/DIS 26101-2:2022
2) Under preparation. Stage at the time of the ballot: ISO/DIS 5114-1:2022
oSIST prEN ISO 3744:2023
ISO/DIS 3744:2022(E)
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3744:2010, Acoustics — Determination of sound power levels and sound energy levels of noise sources
using sound pressure — Engineering methods for an essentially free field over a reflecting plane
ISO 3745, 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/DIS 26101-2:—, 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
ISO/DIS 5114-1:—, Acoustics — Determination of uncertainties associated with sound emission
measures — Part 1: Sound power levels determined from sound pressure measurements
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM: 1995)
IEC 60942, Electroacoustics — Sound calibrators
IEC 61260, Electroacoustics — Octave-band and fractional-octave-band filters
IEC 61672-1, Electroacoustics — Sound level meters — Part 1: Specifications
IEC 61672-3, Electroacoustics — Sound level meters — Part 3: Periodic Testing
IEC 61183, Electroacoustics — Random-incidence and diffuse-field calibration of sound level meters
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 terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
sound pressure
p
difference between instantaneous total pressure and static pressure
Note 1 to entry: Sound pressure is expressed in pascals.
[SOURCE: ISO 80000-8:2020, 8-2.2, modified, Note 1 added.]
oSIST prEN ISO 3744:2023
ISO/DIS 3744:2022(E)
3.2
sound pressure level
L
p
quantity given by:
p
rms
L =10 lg dB
p
p
where p is the root-mean-square sound pressure in the time domain and p is the reference value if
rms 0
sound pressure
t
p = pt()dt
rms
∫
T
t
and p = 20 μPa is the reference value of sound pressure
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
pA
level.
Note 2 to entry: In this version “sound pressure level” is the same definition as “time-average sound pressure
level” in ISO 3744:2010, the changes were made to be consistent with ISO 80000-8:2020.
[SOURCE: ISO 80000-8:2020, table 1, 8-14, modified: deleted remarks and added instead Note 1 to entry
and Note 2 to entry.]
3.4
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 is determined
Note 1 to entry: Measurement time interval is expressed in seconds.
3.5
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.
3.6
acoustic free field over a reflecting plane
essentially acoustic free field over a reflecting plane in the absence of any other obstacles
3.7
reflecting plane
sound reflecting planar surface on which the noise source under test is located
3.8
frequency range of interest
for general purposes, the 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.
oSIST prEN ISO 3744:2023
ISO/DIS 3744:2022(E)
3.9
reference box
hypothetical right parallelepiped terminating on the reflecting plane(s) 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
[18]
pressure measurements at bystander positions in accordance with, for example, ISO 11201 .
3.10
characteristic source dimension
d
o
distance from the origin of the co-ordinate system to the farthest corner of the reference box
Note 1 to entry: Characteristic source dimension is expressed in metres.
3.11
measurement distance
d
distance from the reference box to a parallelepiped measurement surface
Note 1 to entry: Measurement distance is expressed in metres.
3.12
measurement radius
r
radius of a hemispherical, half-hemispherical or quarter-hemispherical measurement surface
Note 1 to entry: Measurement radius is expressed in metres.
3.13
measurement surface
hypothetical surface of area, S , on which the microphone positions are located at which the sound
pressure levels are measured, enveloping the noise source under test and terminating on the reflecting
plane(s) on which the source is located
3.14
background noise
noise from all sources other than the noise source under test
Note 1 to entry: Background noise includes contributions from airborne sound, noise from structure-borne
vibration, and electrical noise in the instrumentation.
3.15
background noise correction
K
correction applied to the mean (energy average) of the sound pressure levels over all the microphone
positions on the measurement surface, to account for the influence of background noise
Note 1 to entry: Background noise correction is expressed in decibels.
Note 2 to entry: The background noise correction is frequency dependent; the correction in the case of a
frequency band is denoted K , where f denotes the relevant mid-band frequency, and that in the case of
1f
A-weighting is denoted K .
1A
oSIST prEN ISO 3744:2023
ISO/DIS 3744:2022(E)
3.16
environmental correction
K
correction applied to the mean (energy average) of the sound pressure levels over all the microphone
positions on the measurement surface, to account for the influence of reflected or absorbed sound,
determined as described in Annex A or in ISO/DIS 26101-2:—.
Note 1 to entry: Environmental correction is expressed in decibels.
Note 2 to entry: The environmental correction is frequency dependent; the correction in the case of a frequency
band is denoted K , where f denotes the relevant mid-band frequency, and that in the case of overall A-weighting
2f
is denoted K ,which is determined from A-weighted sound pressure level measurements.
2A
Note 3 to entry: In general, the environmental correction depends on the area of the measurement surface and
usually K increases with S .
Note 4 to entry: In practice, the K value determined will be a function of both the reflected sound from the test
environment and the shape and arrangement of microphone on the measurement surface used for the K
determination. For the purpose of this standard the differences between K values determined with different
measurement surfaces are assumed to be included in the stated measurement uncertainty for the test method.
3.17
surface sound pressure level
L
p
mean (energy average) of the sound pressure levels over all the microphone positions, or traverses, on
the measurement surface, with the background noise correction, K , and the environmental correction,
K , applied
Note 1 to entry: Surface sound pressure level is expressed in decibels.
3.18
sound power
P
integral over a surface of the product of sound pressure, p , and the component un of the particle velocity
in the direction normal to the surface, at a point on the surface
Note 1 to entry: Sound power is expressed in watts.
Note 2 to entry: The quantity relates to the rate per time at which airborne sound energy is radiated by a source.
[21]
[SOURCE: ISO 80000-8:2020, 8-9, modified: Abbreviation W deleted, Note 1 and 2 to entry added.]
3.19
sound power level
L
W
quantity given by:
P
m
L =10 lg dB
W
P
where P is the magnitude of the sound power and P = 1pW is the reference value of sound power
m 0
Note 1 to entry: If a specific frequency weighting 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 power level.
WA
[21]
[SOURCE: ISO 80000-8:2020 , 8-15, modified: Note 1 to entry added.]
oSIST prEN ISO 3744:2023
ISO/DIS 3744:2022(E)
3.20
noise test code
standard that is applicable to a particular class, family or type of machinery or equipment, which
specifies all of the information necessary to carry out the determination efficiently, declaration and
verification of the noise emission characteristics under standardized conditions.
4 Test environment
4.1 General
The test environments that are applicable for measurements in accordance with this document are:
— a laboratory room or a flat outdoor area which is adequately isolated from background noise (see
4.4) and which provides an acoustic free field over a reflecting plane;
— a room or a flat outdoor area which is adequately isolated from background noise (see 4.4) and
in which an environmental correction can be applied to allow for a limited contribution from the
reverberant field to the sound pressures on the measurement surface.
Environmental conditions having an adverse effect on the microphones used for the measurements
(e.g. strong electric or magnetic fields, wind, impingement of air discharge from the noise source
being tested, high or low temperatures) shall be avoided. The instructions of the manufacturer of the
measuring instrumentation regarding adverse environmental conditions shall be followed.
In an outdoor area, care shall be taken to minimize the effects of adverse meteorological conditions
(e.g. temperature, humidity, wind, precipitation) on the sound propagation and on sound generation
over the frequency range of interest or on the background noise during the course of the measurements.
When a reflecting surface is not a ground plane or is not an integral part of a test room surface,
particular care should be exercised to ensure that the plane does not radiate any appreciable sound due
to vibrations.
4.2 Criterion for acoustic adequacy of test environment
A test room shall provide a measurement surface that lies inside a sound field that is essentially free of
undesired sound reflections from the room boundaries or nearby objects (apart from the floor).
As far as is practicable, the test environment should be free from reflecting objects other than the
reflecting plane(s).
An object in the proximity of the noise source under test is considered to be sound reflecting if its width
(e.g. diameter of a pole or supporting member) exceeds one-tenth of its distance from the reference box.
The reflecting plane(s) shall extend at least 0,5 m beyond the projection of the measurement surface on
the plane(s). The sound absorption coefficient of the reflecting plane(s) shall be less than 0,1 over the
frequency range of interest.
NOTE 1 Smooth concrete or smooth sealed asphalt surface(s) are generally satisfactory.
Annex A outlines the absolute comparison test for determination of the environmental correction K ,
which is the recommended method for qualification of the test environment and accounting for
deviations of the test environment from the ideal condition.
The preferred method for determination of K2 in test environments that are not qualified for K2=0
using one of the methods in ISO 26101-1 or ISO/DIS 26101-2:— is the absolute comparison test described
in this Annex A and Clause 5 of ISO/DIS 26101-2:—. ISO/DIS 26101-2:— also specifies procedures for
determining the magnitude of the environmental correction, K , including the absolute comparison
test and other methods for calculating K from measurement of the total sound absorption in the test
oSIST prEN ISO 3744:2023
ISO/DIS 3744:2022(E)
environment. If the absolute comparison test is not used for the determination of K , then one of the
methods specified in Clauses 6 or 7 of ISO/DIS 26101-2:— may be used as an alternative.
Measurements in accordance with this document are only valid where K ≤ 40, dB .
2A
[3] [4] [6]
NOTE 2 If the environmental correction K exceeds 40, dB, ISO 3743-1, ISO 3743-2, ISO 3747,
2A
[3] [14] [5]
ISO 9614-1 or ISO 9614-2 can be used for results of accuracy grade 2, or ISO 3746 can be used for results of
accuracy grade 3.
NOTE 3 In some specific cases, the horizontal testing plane cannot be reflecting (e.g. lawnmowers, some types
of earth-moving machines). In such cases, a relevant noise test code describes in detail the nature of the plane on
which the noise source is mounted and indicates the possible consequences on the measurement uncertainty.
The environmental correction, K , may be assumed to be zero for measurements made in a hemi-
anechoic room within a measurement volume that has been qualified in accordance with the procedures
outlined in ISO 26101-1, and which meet the criteria in Table A.2 in Annex A of ISO 3745. For
parallelepiped and cylindrical measurements K may be assumed to be zero if the test environment has
been qualified for a volume that includes all positions on the measurement surface in accordance with
the procedures outlined in Clause 7 of ISO/DIS 26101-2:—.
For an outdoor space which consists of a hard, flat ground surface, such as asphalt or concrete, with no
sound-reflecting objects within a distance from the noise source equal to 10 times the greatest distance
from the geometric centre of the source to any of the lowest measurement points, it may be assumed
that the environmental correction K is less than 0,5 dB and may be neglected.
4.3 Criterion for environmental correction
The environmental correcti
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