EN ISO 3741:2010

SLOVENSKI STANDARD
01-december-2010
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SIST EN ISO 3741:2009
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Acoustics - Determination of sound power levels and sound energy levels of noise
sources using sound pressure - Precision methods for reverberation test rooms (ISO
3741:2010)
Akustik - Bestimmung der Schallleistungs- und Schallenergiepegel von Geräusch-
quellen aus Schalldruckmessungen - Hallraumverfahren der Genauigkeitsklasse 1 (ISO
3741:2010)
Acoustique - Détermination des niveaux de puissance acoustique et des niveaux
d'énergie acoustique émis par les sources de bruit a partir de la pression acoustique -
Méthodes de laboratoire en salles d'essais réverbérantes (ISO 3741:2010)
Ta slovenski standard je istoveten z: EN ISO 3741:2010
ICS:
17.140.01 $NXVWLþQDPHUMHQMDLQ Acoustic measurements and
EODåHQMHKUXSDQDVSORãQR noise abatement in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 3741
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2010
ICS 17.140.01 Supersedes EN ISO 3741:2009
English Version
Acoustics - Determination of sound power levels and sound
energy levels of noise sources using sound pressure - Precision
methods for reverberation test rooms (ISO 3741:2010)
Acoustique - Détermination des niveaux de puissance et Akustik - Bestimmung der Schallleistungs- und
des niveaux d'énergie acoustiques émis par les sources de Schallenergiepegel von Geräusch- quellen aus
bruit à partir de la pression acoustique - Méthodes de Schalldruckmessungen - Hallraumverfahren der
laboratoire en salles d'essais réverbérantes (ISO Genauigkeitsklasse 1 (ISO 3741:2010)
3741:2010)
This European Standard was approved by CEN on 14 August 2010.

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 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 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, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2010 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 3741:2010: E
worldwide for CEN national Members.

Contents Page
Foreword .3
Annex ZA .4

Foreword
The text of ISO 3741:2010 has been prepared by Technical Committee ISO/TC 43 “Acoustics” of the
International Organization for Standardization (ISO) and has been taken over as EN ISO 3741:2010 by
Technical Committee CEN/TC 211 “Acoustics” the secretariat of which is held by DS.
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 April 2011, and conflicting national standards shall be withdrawn at the
latest by April 2011.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 3741:2009.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association, and supports essential requirements of EU Directive.
For relationship with EU Directive, see informative Annex ZA, which is an integral part of this document.
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, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 3741:2010 has been approved by CEN as a EN ISO 3741:2010 without any modification.
Annex ZA
(informative)
Relationship between this European Standard and the
Essential Requirements of EU Directive 2006/42/EC

This European Standard has been prepared under a mandate given to CEN by the European Commission
and the European Free Trade Association to provide one means of conforming to Essential Requirements of
the New Approach Directive 2006/42/EC on machinery.
Once this standard is cited in the Official Journal of the European Communities under that Directive and has
been implemented as a national standard in at least one Member State, compliance with the normative
clauses of this standard confers, within the limits of the scope of this standard, a presumption of conformity
with the relevant Essential Requirements of that Directive and associated EFTA regulations.
WARNING — Other requirements and other EU Directives may be applicable to the products falling
within the scope of this standard.
INTERNATIONAL ISO
STANDARD 3741
Fourth edition
2010-10-01
Acoustics — Determination of sound
power levels and sound energy levels of
noise sources using sound pressure —
Precision methods for reverberation test
rooms
Acoustique — Détermination des niveaux de puissance et des niveaux
d'énergie acoustiques émis par les sources de bruit à partir de la
pression acoustique — Méthodes de laboratoire en salles d'essais
réverbérantes
Reference number
ISO 3741:2010(E)
©
ISO 2010
ISO 3741:2010(E)
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ii © ISO 2010 – All rights reserved

ISO 3741:2010(E)
Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Normative references.2
3 Terms and definitions .2
4 Reference meteorological conditions .6
5 Reverberation test room.6
6 Instrumentation and measurement equipment .10
7 Definition, location, installation, and operation of noise source under test.10
8 Measurements in the reverberation test room .12
9 Determination of sound power levels and sound energy levels .19
10 Measurement uncertainty.27
11 Information to be recorded.30
12 Test report.31
Annex A (informative) Guidelines for the design of reverberation test rooms .32
Annex B (informative) Guidelines for the design of rotating diffusing vanes .34
Annex C (normative) Reverberation test room qualification procedure for the measurement of
broad-band sound .35
Annex D (normative) Reverberation test room qualification procedure for the measurement of
discrete-frequency components.37
Annex E (informative) Extension of frequency range to frequencies below 100 Hz.42
Annex F (normative) Calculation of octave band sound power levels and sound energy levels, A-
weighted sound power levels and A-weighted sound energy levels from one-third-octave
band levels .45
Annex G (informative) Guidelines on the development of information on measurement
uncertainty .48
Bibliography.60

ISO 3741:2010(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 3741 was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.
This fourth edition cancels and replaces the third edition (ISO 3741:1999), which has been technically revised.
It also incorporates the Technical Corrigendum ISO 3741:1999/Cor.1:2001.
iv © ISO 2010 – All rights reserved

ISO 3741:2010(E)
Introduction
[2] [8]
This International Standard is one of the series ISO 3740 to ISO 3747 , which specify various methods for
determining the sound power levels and sound energy levels of noise sources including machinery, equipment
and their sub-assemblies. The selection of one of the methods from the series for use in a particular
application depends on the purpose of the test to determine the sound power level or sound energy level and
[2] [2]
on the facilities available. General guidelines to assist in the selection are provided in ISO 3740 . ISO 3740
[8]
to ISO 3747 give only general principles regarding the operating and mounting conditions of the machinery
or equipment for the purposes of the test. It is important that test codes be established for individual kinds of
noise source, in order to give detailed requirements for mounting, loading, and operating conditions under
which the sound power levels or sound energy levels are to be obtained.
The methods given in this International Standard require the source under test to be mounted in a
reverberation test room having specified acoustical characteristics. The methods are then based on the
premise that the sound power or sound energy of the source under test is directly proportional to the
mean-square sound pressure averaged in space and time, and otherwise depends only on the acoustical and
geometric properties of the room and on the physical constants of air.
For a source emitting sound in narrow bands of frequency or at discrete frequencies, a precise determination
of the radiated sound power level or sound energy level in a reverberation test room requires greater effort
than for a source emitting sound more evenly over a wide range of frequencies, because:
a) the space- and time-averaged sound pressure along a short microphone path, or as determined with an
array of a small number of microphones, is not always a good estimate of the space- or time-averaged
mean-square pressure throughout the room;
b) the sound power or sound energy radiated by the source is more strongly influenced by the normal
modes of the room and by the position of the source within the room.
The increased measurement effort in the case of a source emitting narrow bands of sound or discrete tones
consists of either the optimization and qualification of the test room or the use of a greater number of source
locations and microphone positions (or increased path length for a moving microphone). The addition of
low-frequency absorbers or the installation of rotating diffusers in the test room can help to reduce the
measurement effort.
The methods specified in this International Standard permit the determination of the sound power level and
the sound energy level in one-third-octave frequency bands, from which octave band data, A-weighted
frequency data, and total unweighted sound can be computed.
This International Standard describes methods of accuracy grade 1 (precision grade) as defined in ISO 12001.
The resulting sound power levels and sound energy levels include corrections to allow for any differences that
might exist between the meteorological conditions under which the tests are conducted and reference
meteorological conditions. For applications in reverberant environments where reduced accuracy is
[3] [4] [8]
acceptable, reference can be made to ISO 3743-1 , ISO 3743-2 or ISO 3747 .

INTERNATIONAL STANDARD ISO 3741:2010(E)

Acoustics — Determination of sound power levels and sound
energy levels of noise sources using sound pressure —
Precision methods for reverberation test rooms
1 Scope
1.1 General
This International Standard specifies methods for determining the sound power level or sound energy level of
a noise source from sound pressure levels measured in a reverberation test room. The sound power level
(or, in the case of noise bursts or transient noise emission, the sound energy level) produced by the noise
source, in frequency bands of width one-third-octave, is calculated using those measurements, including
corrections to allow for any differences between the meteorological conditions at the time and place of the test
and those corresponding to a reference characteristic impedance. Measurement and calculation procedures
are given for both a direct method and a comparison method of determining the sound power level and the
sound energy level.
In general, the frequency range of interest includes the one-third-octave bands with mid-band frequencies
from 100 Hz to 10 000 Hz. Guidelines for the application of the specified methods over an extended frequency
range in respect to lower frequencies are given in Annex E. This International Standard is not applicable to
frequency ranges above the 10 000 Hz one-third-octave band.
NOTE For higher frequencies, the methods specified in ISO 9295 can be used.
1.2 Types of noise and noise sources
The methods specified in this International Standard are suitable for all types of noise (steady, non-steady,
fluctuating, isolated bursts of sound energy, etc.) defined in ISO 12001.
The noise source under test can be a device, machine, component or sub-assembly. This International
Standard is applicable to noise sources with a volume not greater than 2 % of the volume of the reverberation
test room. For a source with a volume greater than 2 % of the volume of the test room, it is possible that the
achievement of results as defined in ISO 12001:1996, accuracy grade 1 (precision grade) is not feasible.
NOTE In specific cases, the source volume can be increased to a maximum of 5 % of the room volume. In such
cases, the relevant noise test code indicates the possible consequences on the measurement uncertainty.
1.3 Reverberation test room
The test rooms that are applicable for measurements made in accordance with this International Standard are
reverberation test rooms meeting specified requirements (see Clause 5).
1.4 Measurement uncertainty
Information is given on the uncertainty of the sound power levels and sound energy levels determined in
accordance with this International Standard, for measurements made in specific frequency bands and for the
A-weighted sum of all frequency bands. The uncertainty conforms to ISO 12001:1996, accuracy grade 1
(precision grade).
ISO 3741:2010(E)
2 Normative references
The following referenced documents are indispensable for the application 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 3382-2, Acoustics — Measurement of room acoustic parameters — Part 2: Reverberation time in ordinary
rooms
ISO 5725 (all parts), Accuracy (trueness and precision) of measurement methods and results
ISO 6926, Acoustics — Requirements for the performance and calibration of reference sound sources for the
determination of sound power levels
ISO 12001:1996, Acoustics — Noise emitted by machinery and equipment — Rules for the drafting and
presentation of a noise test code
ISO/IEC Guide 98-3, Uncertainty in measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
IEC 60942:2003, Electroacoustics — Sound calibrators
IEC 61183, Electroacoustics — Random-incidence and diffuse-field calibration of sound level meters
IEC 61260:1995, Electroacoustics — Octave-band and fractional-octave-band filters
IEC 61672-1:2002, Electroacoustics — Sound level meters — Part 1: Specifications
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
sound pressure
p
difference between instantaneous pressure and static pressure
[21]
NOTE 1 Adapted from ISO 80000-8:2007 , 8-9.2.
NOTE 2 Sound pressure is expressed in pascals.
3.2
sound pressure level
L
p
ten times the logarithm to the base 10 of the ratio of the square of the sound pressure, p, to the square of a
reference value, p , expressed in decibels
p
L = 10lg dB (1)
p
p
where the reference value, p , is 20 µPa
[20]
[ISO/TR 25417:2007 , 2.2]
NOTE 1 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
2 © ISO 2010 – All rights reserved

ISO 3741:2010(E)
[21]
NOTE 2 This definition is technically in accordance with ISO 80000-8:2007 , 8-22.
3.3
time-averaged sound pressure level
L
p,T
ten times the logarithm to the base 10 of the ratio of the time average of the square of the sound pressure, p,
during a stated time interval of duration, T (starting at t and ending at t ), to the square of a reference value,
1 2
p , expressed in decibels
t
⎡⎤2
⎢⎥
pt()dt
∫
⎢⎥T
t
⎢⎥1
L = 10 lg dB (2)
pT,
⎢⎥
p
⎢⎥
⎢⎥
⎢⎥
⎣⎦
where the reference value, p , is 20 µPa
NOTE 1 In general, the subscript “T” is omitted since time-averaged sound pressure levels are necessarily determined
over a certain measurement time interval.
NOTE 2 Time-averaged sound pressure levels are often A-weighted, in which case they are denoted by L , which is
pA,T
usually abbreviated to L .
pA
[20]
NOTE 3 Adapted from ISO/TR 25417:2007 , 2.3.
3.4
single event time-integrated sound pressure level
L
E
ten times the logarithm to the base 10 of the ratio of the integral of the square of the sound pressure, p, of an
isolated single sound event (burst of sound or transient sound) over a stated time interval T (starting at t and
ending at t ) to a reference value, E , expressed in decibels
2 0
t
⎡⎤2
⎢⎥
pt()dt
∫
⎢⎥
t
⎢⎥
L = 10 lg dB (3)
ET,
⎢⎥
E
⎢⎥
⎢⎥
⎢⎥
⎣⎦
2 −10 2
where the reference value, E , is (20 µPa) s = 4 × 10 Pa s
T
NOTE 1 This quantity can be obtained by L +10lg dB , where T = 1 s.
pT, 0
T
NOTE 2 When used to measure sound immission, this quantity is usually called “sound exposure level”
[20]
(see ISO/TR 25417:2007 ).
3.5
measurement time interval
T
portion or a multiple of an operational period or operational cycle of the noise source under test for which the
time-averaged sound pressure level is determined
NOTE Measurement time interval is expressed in seconds.
ISO 3741:2010(E)
3.6
reverberation test room
test room meeting the requirements of this International Standard
3.7
reverberant sound field
that portion of the sound field in the test room over which the influence of sound received directly from the
source is negligible
3.8
reverberation time
T
n
−n/10
duration required for the space-averaged sound energy density in an enclosure to decrease 10 (i.e. by
n dB) after the source emission has stopped
[21]
[ISO 80000-8:2007 , 8-29]
NOTE 1 Reverberation time is expressed in seconds.
NOTE 2 The reverberation time is frequency dependent.
NOTE 3 For the purposes of this International Standard, n = 60, and the symbol used is T .
3.9
sound absorption coefficient
α
at a given frequency and for specified conditions, the relative fraction of sound power incident upon a surface
which is not reflected
NOTE For the purposes of this International Standard, sound absorption coefficients are calculated in accordance
[1]
with ISO 354 .
3.10
equivalent sound absorption area
A
product of the area and sound absorption coefficient of a surface
NOTE Equivalent sound absorption area is expressed in square metres.
3.11
reference sound source
sound source meeting specified requirements
NOTE For the purposes of this International Standard, the requirements are those specified in ISO 6926:1999,
Clause 5.
3.12
frequency range of interest
for general purposes, the frequency range of one-third-octave bands with nominal mid-band frequencies from
100 Hz to 10 000 Hz
NOTE For special purposes, the frequency range can be extended or reduced, provided that the test environment
and instrumentation otherwise meet all requirements of this International Standard. The frequency range can be extended
downwards as far as the 50 Hz one-third-octave band (see Annex E), but cannot be extended upwards beyond the
10 000 Hz band. Any reduced or extended frequency range is clearly indicated as such in the report.
3.13
background noise
noise from all sources other than the noise source under test
4 © ISO 2010 – All rights reserved

ISO 3741:2010(E)
NOTE Background noise includes contributions from airborne sound, noise from structure-borne vibration, and
electrical noise in the instrumentation.
3.14
background noise correction
K
correction applied to the measured sound pressure levels in the reverberation test room to account for the
influence of background noise
NOTE 1 Background noise correction is expressed in decibels.
NOTE 2 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.
1f
3.15
sound power
P
through a surface, product of the sound pressure, p, and the component of the particle velocity, u , at a point
n
on the surface in the direction normal to the surface, integrated over that surface
[21]
[ISO 80000-8:2007 , 8-16]
NOTE 1 Sound power is expressed in watts.
NOTE 2 The quantity relates to the rate per time at which airborne sound energy is radiated by a source.
3.16
sound power level
L
W
ten times the logarithm to the base 10 of the ratio of the sound power of a source, P, to a reference value, P ,
expressed in decibels
P
L = 10lg dB (4)
W
P
where the reference value, P , is 1 pW
NOTE 1 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]
NOTE 2 This definition is technically in accordance with ISO 80000-8:2007 , 8-23.
[20]
[ISO/TR 25417:2007 , 2.9]
3.17
sound energy
J
integral of the sound power, P, over a stated time interval of duration T (starting at t and ending at t )
1 2
t
J = Pt()dt (5)
∫
t
NOTE 1 Sound energy is expressed in joules.
NOTE 2 The quantity is particularly relevant for non-stationary, intermittent sound events.
[20]
[ISO/TR 25417:2007 , 2.10]
ISO 3741:2010(E)
3.18
sound energy level
L
J
ten times the logarithm to the base 10 of the ratio of the sound energy, J, to a reference value, J , expressed
in decibels
J
L = 10 lg dB (6)
J
J
where the reference value, J , is 1 pJ
NOTE 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 energy level.
JA
[20]
[ISO/TR 25417:2007 , 2.11]
4 Reference meteorological conditions
Reference meteorological conditions for the purpose of determining the sound power level and sound energy
level are:
a) air temperature: 23,0 °C;
b) static pressure: 101,325 kPa;
c) relative humidity: 50 %.
5 Reverberation test room
5.1 General
The reverberation test room shall be large enough and have a low enough total sound absorption to provide
an adequate reverberant sound field for all frequency bands within the frequency range of interest. Guidelines
for the design of rooms suitable for use in determining sound power levels and sound energy levels in
accordance with this International Standard are given in Annex A. Guidelines for the design of rotating
diffusing vanes in the room are given in Annex B.
5.2 Volume and shape of test room
The recommended minimum volume of the room is given in Table 1. All test rooms should be qualified using
Annex C. For test rooms with volumes less than the values shown in Table 1 for the frequency range of
interest, or with a volume exceeding 300 m , the adequacy of the room for broadband measurements shall be
demonstrated using the procedure specified in Annex C. A room qualification procedure for the measurement
of discrete-frequency components is specified in Annex D, which also specifies a general room qualification
procedure as an alternative to qualification of individual sources (using 8.4.2 or 8.5.2). Information is given in
Annex E to assist in testing at frequencies below 100 Hz.
6 © ISO 2010 – All rights reserved

ISO 3741:2010(E)
Table 1 — Recommended minimum volume of the reverberation test room as
a function of the lowest frequency band of interest
Lowest one-third-octave band Minimum volume of the reverberation
frequency of interest test room

Hz m
100 200
125 150
160 100
W200 70
5.3 Sound absorption of test room
The sound absorption of the test room primarily affects the minimum distance to be maintained between the
noise source under test and the microphone positions. It also influences the sound radiation of the source and
the frequency response characteristics of the test space. For these reasons, the sound absorption of the test
room shall be neither too large nor extremely small (see Annex A).
Over the frequency range of interest, all room surfaces within one wavelength of the noise source under test
shall be designed to be reflective with an absorption coefficient less than 0,06. If low-frequency panel
absorbers are required as per Annex C and/or Annex D, these devices may be mounted within one
wavelength (at the lowest frequency of interest) of the noise source under test, but not closer than 1,5 m. The
remaining surfaces shall have absorptive properties such that the reverberation time, T (for measurement,
see 8.7), in seconds, in each one-third-octave band below 6.3 kHz, without the source under test in place, is
numerically greater than the ratio of V and S:
V
T > (7)
S
where
V is the volume, expressed in cubic metres, of the reverberation test room;
S is the total surface area, expressed in square metres, of the test room.
If the requirement for the reverberation time given by Inequality (6) is not met, the adequacy of the room for
broadband measurements shall be established by the procedure specified in Annex C.
NOTE Above 5 kHz, much of the absorption in the room is due to air. Keeping the relative humidity above 50 % helps
to avoid excessive air absorption.
5.4 Criteria for background noise
5.4.1 Relative criteria for background noise
5.4.1.1 General
The time-averaged sound pressure level of the background noise in each frequency band within the frequency
range of interest, measured and averaged (see 9.1.3 and 9.2.3) over the microphone positions or traverses,
shall be below the corresponding time-averaged sound pressure level of the noise source under test by at
least:
a) 6 dB for one-third-octave bands of mid-band frequency 200 Hz and below and 6 300 Hz and above;
ISO 3741:2010(E)
b) 10 dB for one-third-octave bands of mid-band frequency from 250 Hz to 5 000 Hz.
If these requirements are met, the background noise criteria of this International Standard are satisfied.
NOTE 1 The same criteria are applied to single event time-integrated sound pressure levels: the measurement time
interval for the time average is the same as the measurement time interval associated with the single event.
NOTE 2 The noise associated with the microphone traversing mechanism, if one is used for the measurements, is
considered to be part of the background noise. In such cases, the background noise is measured with the traversing
mechanism operating.
5.4.1.2 Relative background noise criteria for frequency band measurements
The requirements of 5.4.1.1 may not be achievable in all frequency bands, even when the background noise
levels in the test room are extremely low and well controlled. Therefore, any band within the frequency range
of interest in which the A-weighted sound power level or sound energy level (see Annex F) of the noise source
under test (after correcting for background noise in accordance with 9.1.2 or 9.2.2) is at least 15 dB below the
highest A-weighted band sound power or sound energy level may be excluded from the frequency range of
interest for the purposes of determining compliance with the above criterion for background noise.
5.4.1.3 Relative background noise criteria for A-weighted measurements
If the A-weighted sound power level or sound energy level is to be determined and reported, the following
steps shall be followed to determine whether this quantity meets the background noise criteria of this
International Standard:
a) the A-weighted sound power level or sound energy level is computed in accordance with the procedures
in this International Standard using the data from every frequency band within the frequency range of
interest;
b) the computation is repeated, but excluding those bands for which ∆L < 6 dB for one-third-octave bands
p
of mid-band frequency 200 Hz and below and 6 300 Hz and above, and for which ∆L < 10 dB for
p
one-third-octave bands of mid-band frequency from 250 Hz to 5 000 Hz.
If the difference between these two levels is less than 0,5 dB, the A-weighted sound power level or sound
energy level determined from the data for all bands may be considered as conforming to the background
noise criteria of this International Standard.
5.4.2 Absolute criteria for background noise
If it can be demonstrated that the background noise levels in the test room at the time of the measurements
are less than or equal to those given in Table 2 for all bands within the frequency range of interest, the
measurements can be taken as having met the background noise requirements of this International Standard,
even if the 6 dB or 10 dB requirements are not met for all bands. It can be assumed that the source emits little
or no measurable noise in these frequency bands, and that the data reported represent an upper bound to the
sound power level or sound energy level in these bands.
In the case where some of the measured levels from the source under test are less than or equal to those
given in Table 2, the frequency range of interest may be restricted to a contiguous range of frequencies that
includes both the lowest and highest frequencies at which the sound pressure level from the noise source
exceeds the corresponding value in Table 2. In such cases, the applicable frequency range of interest shall be
reported.
5.4.3 Statement of non-conformity with background noise criteria
If neither the relative criteria of 5.4.1 nor the absolute criteria in 5.4.2 are met, the report shall clearly state that
the background noise requirements of this International Standard have not been met, and shall identify the
particular frequency bands that do not meet the criteria. Furthermore, the report shall not state or imply that
the measurements have been made “in full conformity” with this International Standard.
8 © ISO 2010 – All rights reserved

ISO 3741:2010(E)
Table 2 —Absolute maximum background noise levels in test room
One-third-octave mid- Maximum band sound
band frequency pressure level
Hz dB
50 42
63 39
80 36
100 33
125 30
160 27
200 24
250 21
315 18
400 15
500 12
630 11
800 11
1 000 10
1 250 10
1 600 10
2 000 10
2 500 10
3 150 10
4 000 10
5 000 10
6 300 10
8 000 10
10 000 10
5.5 Atmospheric temperature, humidity and pressure
In the region where the microphones are located, the variations of atmospheric temperature and relative
humidity shall be within the limits shown in Table 3.
Measurements of atmospheric pressure shall be made to within ±1,5 kPa.
The limits of Table 3 are generally sufficient. However, other temperature and humidity conditions may be
specified in noise test codes for specific equipment types, especially if the operation of the equipment or noise
emission levels depend on ambient conditions. In such cases, those conditions shall be applied.
Table 3 — Allowable limits in the variation of atmospheric temperature and
relative humidity during measurements in the reverberation test room
Ranges of relative humidity
Ranges of
temperature
%
θ
< 30 % 30 % to 50 % > 50 %
°C
Allowable limits for temperature and relative humidity
− 5 u θ < 10 ± 1 °C, ± 3 % ± 1 °C, ± 5 % ± 3 °C, ± 10 %
10 u θ < 20 ± 1 °C, ± 3 % ± 3 °C, ± 5 % ± 3 °C, ± 10 %
20 u θ u 50 ± 2 °C, ± 3 % ± 5 °C, ± 5 % ± 5 °C, ± 10 %

ISO 3741:2010(E)
6 Instrumentation and measurement equipment
6.1 General
The instrumentation system, including the microphones and cables, shall meet the requirements of
IEC 61672-1:2002, class 1, and the filters shall meet the requirements of IEC 61260:1995, class 1. The
reference sound source, if employed for the comparison method (see 8.1), shall meet the requirements given
in ISO 6926.
6.2 Calibration
The microphones shall be calibrated for random incidence as specified in IEC 61183.
Before and after each series of measurements, a sound calibrator meeting the requirements of
IEC 60942:2003, class 1 shall be applied to each microphone to verify the calibration of the entire measuring
system at one or more frequencies within the frequency range of interest. Without any further adjustment, the
difference between the readings made before and after each series of measurements shall be less than or
equal to 0,5 dB. If this value is exceeded, the results of the series of measurements shall be discarded.
The calibration of the sound calibrator, the compliance of the instrumentation system with the requirements of
IEC 61672-1, the compliance of the filter set with the requirements of IEC 61260, and, if used, the compliance
of the reference sound source with the requirements of ISO 6926, shall be verified at intervals in a laboratory
making calibrations traceable to appropriate standards.
Unless national regulations dictate otherwise, it is recommended that the sound calibrator should be calibrated
at intervals not exceeding 1 year, the reference sound source should be calibrated at intervals not exceeding
2 years, the compliance of the instrumentation system with the requirements of IEC 61672-1 should be
verified at intervals not exceeding 2 years, and the compliance of the filter set with the requirements of
IEC 61260 should be verified at intervals not exceeding 2 years.
7 Definition, location, installation, and operation of noise source under test
7.1 General
It is important to decide which components, sub-assemblies, auxiliary equipment, power sources, etc.,
constitute integral parts of the noise source whose sound power level or sound energy level is to be
determined. It is important also to define the manner in which the source is installed and operated for the test,
since both these factors can have a significant influence on the sound power or sound energy emitted. This
clause describes the approach to be adopted in setting up the source for testing and in defining the conditions,
so as to achieve an arrangement which is reproducible and which can be related clearly to the results
obtained.
This International Standard gives general specifications relating to noise source definition, installation and
operation, but these are overridden by the instructions and specifications of a noise test code, if any exists, for
the particular type of source under test.
7.2 Auxiliary equipment
Care shall be taken to ensure that any electrical conduits, piping or air ducts connected to the noise source
under test do not radiate significant amounts of sound energy into the test environment.
If practicable, all auxiliary equipment necessary for the operation of the noise source under test that is not a
part of it shall be located outside the reverberation test room. If this is impractical, care shall be taken to
minimize any sound radiated into the room from such equipment. The noise source under test shall be taken
to include all significant sources of sound emission, including auxiliary equipment which cannot either be
removed or adequately quietened.
10 © ISO 2010 – All rights reserved

ISO 3741:2010(E)
7.3 Noise source location
The noise source to be tested shall be installed in the reverberation test room at one or more locations relative
to the boundary surfaces, as if it were in normal use. If a particular position is not otherwise specified, the
source shall be placed on the floor at least 1,5 m from any wall of the room. If two or more source positions
are necessary in accordance with 8.4.2.4 or Annex D, the distance between different positions shall be equal
to or larger than the half wavelength of sound corresponding to the lowest mid-band frequency of
measurement. In the case of a test room having a rectangular floor, the noise source under test shall be
placed asymmetrically on the floor.
Tabletop equipment shall be placed on the floor of the reverberation test room, at least 1,5 m from any wall,
unless a table or stand is considered essential for normal operation. In the latter case, the equipment shall be
placed at the centre of the tabletop, and the source and table shall be regarded as an integral whole for the
purpose of the test.
7.4 Installation and mounting conditions
In many cases, the sound power or sound energy emitted by a source is affected by the support or mounting
conditions. Whenever a typical condition of mounting exists for the noise source under test, that condition
shall be used or sim
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