EN ISO 3745:2003

SLOVENSKI STANDARD
01-september-2004
$NXVWLND8JRWDYOMDQMHUDYQL]YRþQLKPRþLYLURYKUXSD3UHFL]LMVNDPHWRGD]D
JOXKHLQSROJOXKHSURVWRUH,62
Acoustics - Determination of sound power levels of noise sources using sound pressure -
Precision methods for anechoic and semi-anechoic rooms (ISO 3745:2003)
Akustik - Bestimmung der Schallleistungspegel von Geräuschquellen aus
Schalldruckmessungen - Verfahren der Genauigkeitsklasse 1 für reflexionsarme Räume
und Halbräume (ISO 3745:2003)
Acoustique - Détermination des niveaux de puissance acoustique émis par les sources
de bruit a partir de la pression acoustique - Méthodes de laboratoire pour les salles
anéchoiques et semi-anéchoiques (ISO 3745:2003)
Ta slovenski standard je istoveten z: EN ISO 3745:2003
ICS:
17.140.01 $NXVWLþQDPHUMHQMDLQ Acoustic measurements and
EODåHQMHKUXSDQDVSORãQR noise abatement in general
91.120.20 $NXVWLNDYVWDYEDK=YRþQD Acoustics in building. Sound
L]RODFLMD insulation
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 3745
NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2003
ICS 17.140.01
English version
Acoustics - Determination of sound power levels of noise
sources using sound pressure - Precision methods for anechoic
and hemi-anechoic rooms (ISO 3745:2003)
Acoustique - Détermination des niveaux de puissance Akustik - Bestimmung der Schallleistungspegel von
acoustique émis par les sources de bruit à partir de la Geräuschquellen aus Schalldruckmessungen - Verfahren
pression acoustique - Méthodes de laboratoire pour les der Genauigkeitsklasse 1 für reflexionsarme Räume und
salles anéchoïques et semi-anéchoïques (ISO 3745:2003) Halbräume (ISO 3745:2003)
This European Standard was approved by CEN on 3 November 2003.
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 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 Management Centre has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2003 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 3745:2003 E
worldwide for CEN national Members.

CORRECTED  2004-03-03
Foreword
This document (EN ISO 3745:2003) 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 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 June 2004, and conflicting national
standards shall be withdrawn at the latest by June 2004.
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(s).
For relationship with EU Directive(s), see informative Annex ZB, 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, Czech
Republic, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,
Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and
the United Kingdom.
Endorsement notice
The text of ISO 3745:2003 has been approved by CEN as EN ISO 3745:2003 without any
modifications.
NOTE Normative references to International Standards are listed in Annex ZA (normative).
Annex ZA
(normative)
Normative references to international publications
with their relevant European publications
This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions of
any of these publications apply to this European Standard only when incorporated in it by
amendment or revision. For undated references the latest edition of the publication referred to
applies (including amendments).
NOTE Where an International Publication has been modified by common modifications, indicated
by (mod.), the relevant EN/HD applies.
Publication Year Title EN Year
ISO 7574-1 1985 Acoustics - Statistical methods for EN 27574-1 1988
determining and verifying stated
noise emission values of machinery
and equipment - Part 1: General
considerations and definitions
ISO 7574-4 1985 Acoustics - Statistical methods for EN 27574-4 1988
determining and verifying stated
noise emission values of machinery
and equipment - Part 4: Methods
for stated values for batches of
machines
ANNEX ZB
(informative)
Relationship between this European Standard and the Essential
Requirements of EU Directive 98/37 EEC
This European Standard has been prepared under a mandate given to CEN by the European

Commission and the European Free Trade Association to provide a means of conforming to
Essential Requirements of the New Approach Directive 98/37 EEC.
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 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.
WARNING: Other requirements and other EU Directives may be applicable to the product(s)
falling within the scope of this standard.
INTERNATIONAL ISO
STANDARD 3745
Second edition
2003-12-01
Acoustics — Determination of sound
power levels of noise sources using
sound pressure — Precision methods for
anechoic and hemi-anechoic rooms
Acoustique — Détermination des niveaux de puissance acoustique
émis par les sources de bruit à partir de la pression acoustique —
Méthodes de laboratoire pour les salles anéchoïques et semi-
anéchoïques
Reference number
ISO 3745:2003(E)
©
ISO 2003
ISO 3745:2003(E)
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ii © ISO 2003 — All rights reserved

ISO 3745:2003(E)
Contents Page
Foreword. v
Introduction . vi
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 2
4 Measurement uncertainty. 5
5 Test room requirements. 6
5.1 General. 6
5.2 Criterion for adequacy of the test room . 7
5.3 Criterion for background noise . 7
5.4 Criterion for temperature. 7
5.5 Humidity correction . 7
6 Instrumentation . 7
6.1 General. 7
6.2 Calibration. 8
7 Installation and operation of source under test.8
7.1 General. 8
7.2 Source location . 8
7.3 Source mounting. 8
7.4 Auxiliary equipment. 9
7.5 Operation of source under test . 9
8 Measurement of sound pressure levels for the determination of sound power level . 10
8.1 General. 10
8.2 Measurement surface . 10
8.3 Microphone positions. 11
8.4 Conditions of measurement. 12
8.5 Data to be obtained. 13
8.6 Correction for background sound pressure levels . 13
8.7 Calculation of surface sound pressure level . 14
9 Measurement of single-event sound pressure levels for the determination of sound
energy level . 15
10 Calculation of sound power level and sound energy level. 16
10.1 Sound power level . 16
10.2 Sound energy level . 17
11 Information to be recorded . 17
11.1 General. 17
11.2 Sound source under test. 18
11.3 Acoustic environment . 18
11.4 Instrumentation . 18
11.5 Acoustic data. 18
12 Information to be reported . 19
Annex A (normative) General procedures for qualification of anechoic and hemi-anechoic rooms . 20
Annex B (normative) Alternative qualification procedure for anechoic and hemi-anechoic rooms
for the determination of sound power levels of specific noise sources. 26
ISO 3745:2003(E)
Annex C (normative) Array of microphone positions in a free field.28
Annex D (normative) Array of microphone positions in a free field over a reflecting plane .29
Annex E (normative) Coaxial circular paths of microphones in a hemi-free field .31
Annex F (normative) Meridional paths of microphones in a hemi-free field .32
Annex G (normative) Spiral paths of microphones in a hemi-free field.34
Annex H (normative) Calculation of A-weighting sound power level from one-third-octave-band
sound power levels .35
Annex I (normative) Calculation of directivity index and directivity factor .37
Annex J (informative) Measurement uncertainty.38
Annex K (informative) Guidelines for the design of test rooms.41
Bibliography.43

iv © ISO 2003 — All rights reserved

ISO 3745:2003(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 3745 was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.
This second edition cancels and replaces the first edition (ISO 3745:1977), which has been technically revised.
ISO 3745:2003(E)
Introduction
0.1 This International Standard is one of the ISO 3740 series, which specifies various methods for
determining the sound power levels of machines, equipment and other sub-assemblies. When selecting one
of the methods of the ISO 3740 series, it is necessary to select the most appropriate for the conditions and
purpose of the test. General guidelines to assist in the selection are provided in ISO 12001 and ISO 3740. The
ISO 3740 series gives only general principles regarding the operating and mounting conditions of the source
under test. Reference should be made to the noise test code for a specific type of machine or equipment, if
available, for specifications on mounting and operating conditions.
0.2 This International Standard specifies a laboratory method for determining the sound power radiated by
sources using an anechoic test room or a hemi-anechoic test room having specified acoustical characteristics.
The method specified in this International Standard is only applicable to indoor measurements in specialized
test rooms.
0.3 This International Standard specifies a laboratory method for the determination of not only sound power
levels but also sound energy levels of sound sources. For a single burst of sound energy or transient sound,
the sound power level cannot be defined and so it is necessary to adopt the sound energy level in order to
specify the emitted sound with such a time history. The application of sound energy levels will be considered
in the future revision of other standards of the ISO 3740 series.
0.4 In this International Standard, the sound power level or sound energy level for reference meteorological
conditions is determined. This is required especially for grade 1 measurements.

vi © ISO 2003 — All rights reserved

INTERNATIONAL STANDARD ISO 3745:2003(E)

Acoustics — Determination of sound power levels of noise
sources using sound pressure — Precision methods for
anechoic and hemi-anechoic rooms
1 Scope
This International Standard specifies methods for measuring the sound pressure levels on a measurement
surface enveloping a noise source in anechoic and hemi-anechoic rooms, in order to determine the sound
power level or sound energy level produced by the noise source. It gives requirements for the test
environment and instrumentation, as well as techniques for obtaining the surface sound pressure level from
which the sound power level or sound energy level is calculated, leading to results which have a grade 1
accuracy.
The methods specified in this International Standard are suitable for measurements of all types of noise.
The noise source can be a device, machine, component or sub-assembly. The maximum size of the source
under test depends on the radius of the hypothetical sphere (or hemisphere) used as the enveloping
measurement surface.
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 7574-1:1985, Acoustics — Statistical methods for determining and verifying stated noise emission values
of machinery and equipment — Part 1: General considerations and definitions
ISO 7574-4:1985, Acoustics — Statistical methods for determining and verifying stated noise emission values
of machinery and equipment — Part 4: Methods for stated values for batches of machines
ISO 9613-1:1993, Acoustics — Attenuation of sound during propagation outdoors — Part 1: Calculation of the
absorption of sound by the atmosphere
IEC 60942:2003, Electroacoustics — Sound calibrators
IEC 61260:1995, Electroacoustics — Octave-band and fractional-octave-band filters
IEC 61672-1:2002, Electroacoustics — Sound level meters — Part 1: Specifications
1)
GUM:1993 , Guide to the expression of uncertainty in measurement. BIPM/IEC/IFCC/ISO/IUPAC/IUPAP/
OIML (ISBN 92-67-10188-9)
1) Corrected and reprinted in 1995.
ISO 3745:2003(E)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
instantaneous sound pressure
p(t)
value at a particular instant in time of the fluctuating pressure that is superimposed on the atmospheric static
pressure due to the presence of a sound wave, and existing at a given point in space, in a stated frequency
band
NOTE It is expressed in pascals.
3.2
sound pressure
p
in space, the root mean square pressure determined over a specified time interval of the instantaneous sound
pressure
NOTE It is expressed in pascals.
3.3
sound pressure level
L
p
ten times the logarithm to the base 10 of the ratio of the time-mean-square of the instantaneous sound
−5
pressure to the square of the reference sound pressure p [p = 20 µPa (2 × 10 Pa)]
0 0
p
L = 10 lg dB (1)
p
p
NOTE 1 Sound pressure levels are expressed in decibels.
NOTE 2 The frequency weighting or the width of the frequency band used and the time weighting should be indicated.
EXAMPLE The A-weighted sound pressure level with time weighting S is L .
pAS
3.3.1
time-averaged sound pressure level
L
peq,T
sound pressure level of a steady or fluctuating sound over the measurement time interval T: ten times the
logarithm to the base 10 of the ratio of the time-mean-square of the instantaneous sound pressure, during a
stated time interval, to the square of the reference sound pressure
T

pt
()

L = 10 lg dt dB (2)
pTeq,
∫ 2
T
p

NOTE In general, the subscripts “eq” and “T” are omitted since time-averaged sound pressure levels are necessarily
determined over a certain measurement time interval.
3.3.2
measurement time interval
time interval for which the time-averaged sound pressure level is determined
2 © ISO 2003 — All rights reserved

ISO 3745:2003(E)
3.4
measurement surface
hypothetical surface of area S, enveloping the source, on which the measurement positions are located
NOTE In the case of a hemi-anechoic room, the measurement surface terminates on the reflecting plane.
3.5
surface sound pressure level
L
pf
energy-average of the time-averaged sound pressure levels at all the microphone positions on the
measurement surface, with the background noise correction K (3.18) applied
N

1 0,1 L
pi
L = 10 lg10 dB (3)
pf ∑
N

i=1
where
L is the surface sound pressure level, in decibels;
pf
L is the sound pressure level corrected for background noise resulting from the ith microphone
pi
position, in decibels;
N is the number of microphone positions.
NOTE It is expressed in decibels.
3.6
sound power
W
rate at which airborne sound energy is radiated by a source
NOTE It is expressed in watts.
3.7
sound power level
L
W
ten times the logarithm to the base 10 of the ratio of the sound power radiated by the sound source under test
−12
to the reference sound power W [W = 1 pW (10 W)]
0 0
W
L = 10 lg dB (4)
W
W
NOTE 1 It is expressed in decibels.
NOTE 2 The frequency weighting or the width of the frequency band used should be indicated.
3.8
single-event sound pressure level
L
pE
sound pressure level of a single burst of sound or transient sound, given by the formula
t
2
pt
()

Lt= 10 lg d dB (5)
pE
∫

pT
t


ISO 3745:2003(E)
where
p(t) is the instantaneous sound pressure;
p = 20 µPa
t − t is a stated time interval long enough to encompass all significant sound of a stated event;

2 1
T = 1 s
NOTE 1 It is expressed in decibels.
NOTE 2 Other standards refer to this quantity as “sound exposure level”.
3.9
sound energy
E
sound energy of a single burst of sound or transient sound radiated by the sound source
T
E = Wt()dt (6)
∫
NOTE It is expressed in joules.
3.10
sound energy level
L
J
ten times the logarithm to the base 10 of the ratio of the sound energy, E (in joules), radiated by the sound
−12
source under test to the reference sound energy, E [E = 1 pJ (10 J)]
0 0
E
L = 10 lg dB (7)
J
E
NOTE 1 It is expressed in decibels.
NOTE 2 The frequency weighting or the width of the frequency band used should be indicated.
3.11
free field
sound field in a homogeneous, isotropic medium, free of boundaries
NOTE In practice, it is a field in which reflections at the boundaries are negligible over the frequency range of interest.
3.12
anechoic room
room in which a free field is obtained
3.13
free field over a reflecting plane
hemi-free field
sound field in a homogeneous, isotropic medium in the half-space above an infinite, rigid plane surface
3.14
hemi-anechoic room
room in which a free field over a reflecting plane is obtained
4 © ISO 2003 — All rights reserved

ISO 3745:2003(E)
3.15
frequency range of interest
one-third-octave bands having centre frequencies from 100 Hz to 10 000 Hz
NOTE For special purposes, the range may be extended or reduced at either end, provided the test room and
instrument accuracy are satisfactory for use over the extended or reduced frequency range.
3.16
measurement radius
r
radius of a spherical or hemi-spherical measurement surface
3.17
background noise
noise from all sources other than the source under test
NOTE Background noise may include contributions from airborne sound, structure-borne vibration, and electrical
noise in instrumentation.
3.18
background noise correction
K
1i
correction term to account for the influence of background noise on the measurements at each microphone
position
NOTE K is frequency dependent and is expressed in decibels.
1i
3.19
directivity index
D
I
measure of the extent to which a source radiates sound predominantly in one direction
NOTE It is expressed in decibels.
4 Measurement uncertainty
If a particular noise source were to be transported to each of a number of different laboratories, and if, at each
laboratory, the sound power level of that source were to be determined in accordance with this International
Standard, the results would show a scatter. The standard deviation of the measured levels could be calculated
(see examples in ISO 7574-4:1985, B.2.1) and would vary with frequency. With few exceptions, these
standard deviations would not exceed those listed in Table 1. The values given in Table 1 are standard
deviations of reproducibility, σ , as defined in ISO 7574-1. The values of Table 1 take into account the
R
cumulative effects of measurement uncertainty in applying the procedures of this International Standard, but
exclude variations in the sound power output caused by changes in operating conditions (e.g. rotational speed,
line voltage) or mounting conditions.
The expanded measurement uncertainty of determinations of sound power level or sound energy level, for a
coverage probability of 95 % (coverage factor k = 2) as defined in the GUM, shall be taken to be two times the
standard deviation of reproducibility, unless more specific knowledge is available (e.g. in the laboratory
undertaking the measurements or in a noise test code for the particular family of noise sources).
ISO 3745:2003(E)
Table 1 — Estimated upper values of the standard deviations of reproducibility of sound power levels
and sound energy levels determined in accordance with this International Standard
One-third-octave midband frequency Upper values of standard deviation of reproducibility, σ
R
Hz dB
Anechoic room Hemi-anechoic room
a
50 to 80 2,0 2,0
100 to 630 1,0 1,5
800 to 5 000 0,5 1,0
6 300 to 10 000 1,0 1,5
b
12 500 to 20 000 2,0 2,0
A-weighted 0,5 0,5
a
If the sound field is qualified according to Clause 5.

b
If the instrumentation allows and if correction is made for absorption of sound by the atmosphere.

NOTE 1 The standard deviations listed in Table 1 are associated with the test conditions and procedures defined in this
International Standard and not with the noise source itself. They arise in part from variations between measurement
laboratories, the geometry of the test room, the acoustical properties of the reflecting plane, absorption at the test room
boundaries, background noise, and the type and calibration of instrumentation. They are also due to variations in
experimental techniques, including the size of the measurement surface, number and location of microphone positions,
sound source location and integration times. The standard deviations are also affected by uncertainties associated with
measurements taken in the near field of the source; such uncertainties depend upon the nature of the sound source, but
generally increase for smaller measurement distances and lower frequencies (below 250 Hz).
NOTE 2 For some sound sources, the standard deviations of reproducibility may be smaller than the values given in
Table 1. Hence, a noise test code for a particular type of machinery or equipment making reference to this International
Standard may state standard deviations smaller than those listed in Table 1, if substantiation is available from the results
of suitable interlaboratory tests.
The standard deviations of reproducibility, as tabulated in Table 1, include the variability associated with
repeated measurements on the same noise source under the same conditions (for standard deviation of
repeatability, see ISO 7574-1). This uncertainty is usually much smaller than the uncertainty associated with
interlaboratory variability. However, if it is difficult to maintain stable operating or mounting conditions for a
particular source, the standard deviation of repeatability may not be small compared with the values given in
Table 1. In such cases, the fact that it was difficult to obtain repeatable sound power level data on the source
should be recorded and stated in the test report.
NOTE 3 The standard deviations of reproducibility given in Table 1 are obtained from interlaboratory tests. This method
of presenting information relating to measurement uncertainty is not in accordance with the requirements of the GUM. At
the time when this International Standard was being prepared, insufficient information was available on which to draw up a
statement which was in accordance with the GUM. However, an indication of the kind of information which would need to
be included in such a statement is given in Annex J.
5 Test room requirements
5.1 General
The test rooms that are applicable for measurements according to this International Standard are either
a) a room which provides a free field or a free field over a reflecting plane and satisfies Annex A over the
frequency range of interest, or
6 © ISO 2003 — All rights reserved

ISO 3745:2003(E)
b) for the purposes of determination of sound power levels of specific noise sources, a room which provides
a free field or a free field over a reflecting plane and satisfies Annex B over the frequency range of
interest.
The requirements of this International Standard shall be met, as a minimum, over the frequency range of
interest. If the requirements can only be met over a more limited frequency range, this fact shall be clearly
stated in the report and any claim of “conformance with ISO 3745” shall only be made over this stated, limited
frequency range.
5.2 Criterion for adequacy of the test room
Annexes A and B describe procedures for determining the extent of deviations of the test room from the ideal
free field condition or the ideal hemi-free field condition, and criteria are given to assess the adequacy of the
test room. Qualification procedures for the test room shall be referred to Annex A or Annex B.
NOTE If it is necessary to make measurements in spaces in which deviations from the inverse square law exceed the
values shown in Annexes A and B, see ISO 3744, ISO 3746, ISO 9614-1 or ISO 9614-2.
5.3 Criterion for background noise
At all microphone positions on the measurement surface and in each frequency band in the frequency range
of interest, the level of background noise shall be at least 10 dB below the sound pressure level due to the
source under test. A-weighted sound power determinations may be made which include some bands where
this criterion is not satisfied, provided that the summed A-weighted background noise of these bands is 10 dB
or more below the A-weighted sound pressure level summed from all bands.
5.4 Criterion for temperature
The air temperature during the measurements shall be within the range of 15 °C to 30 °C.
NOTE The range of temperature is limited in order to guarantee a bias smaller than 0,2 dB when using Equation (15)
for noise sources having different noise generation mechanisms.
5.5 Humidity correction
Over an air temperature range from 15 °C to 30 °C, the maximum correction for humidity is approximately
0,04 dB and may be ignored.
6 Instrumentation
6.1 General
The acoustical instrumentation system, including the microphones and cables, shall meet the requirements for
a class 1 instrument specified in IEC 61672-1:2002. The filters used shall meet the requirements for a class 1
instrument specified in IEC 61260:1995.
The orientation of the microphone shall be that for which it has been calibrated.
Either the manufacturer’s instructions or the requirements from a specific test code should be followed for
selecting the most appropriate orientation for the conditions of the test. In the absence of these, the
microphone should be oriented along the normal to the measurement surface at the point on the surface
closest to the microphone.
The instrument used to determine barometric pressure shall have an uncertainty equal to or better than 2 %.
The instrument used to determine temperature shall have an uncertainty equal to or better than 1 °C. The
instrument used to determine relative humidity shall have an uncertainty equal to or better than 10 %.
ISO 3745:2003(E)
6.2 Calibration
During each series of measurements, a sound calibrator with an accuracy of class 1 as specified in
IEC 60942:2003 shall be applied to the microphone to verify the calibration of the entire measuring system at
one or more frequencies over the frequency range of interest.
The calibrator shall be calibrated and the compliance of the instrumentation system with the requirements of
IEC 61672-1 shall be verified periodically in a manner that is traceable to appropriate standards.
7 Installation and operation of source under test
7.1 General
The manner in which the source under test is installed and operated may have a significant influence on the
sound power emitted by the source. This clause specifies conditions that minimize variations in the sound
power output due to the installation and operating conditions of the source under test. The instructions of a
noise test code, if any exists, shall be followed in so far as installation and operation of the source under test
is concerned.
7.2 Source location
In locating the source within the test room, it is important to allow sufficient space so that the measurement
surface can envelop the source under test in accordance with the requirements of 8.2.
Detailed information on installation conditions and the configuration of the microphone array shall be based on
the general requirements of this International Standard and specific noise test codes for such sources.
7.3 Source mounting
7.3.1 General
In many cases, the sound power emitted will depend upon the support or mounting conditions of the source
under test. Whenever a typical condition of mounting exists for the equipment under test, that condition shall
be used or simulated.
If the support or mounting conditions for the source under test are specified in a specific test code, those
conditions shall be used. If such a specification does not exist, but if a principal or typical condition of support
or mounting exists, then that shall be used for the test. In all these cases, care shall be taken to avoid
changes in the sound output of the source caused by the mounting system employed for the test. Steps shall
be taken to reduce any sound radiation from the structure on which the source under test may be mounted.
NOTE Many small sound sources, although themselves poor radiators of low frequency sound, can, as a result of an
inappropriate method of mounting, radiate more low frequency sound when their vibrational energy is transmitted to
surfaces large enough to be efficient radiators.
7.3.2 Hand-held noise sources
Hand-held noise sources shall be held or guided by hand. If the source under test requires a support for its
operation, the support structure shall be small, considered to be a part of the source under test, and described
in the machine test code.
7.3.3 Base-mounted and wall-mounted noise sources
Base-mounted and wall-mounted noise sources shall be placed on a reflecting (acoustically hard) plane (floor
and wall). Table top equipment shall be placed on the floor, unless a table or stand is required for operation
according to the test code for the equipment under test. Such equipment shall be placed in the centre of the
top of the test table.
8 © ISO 2003 — All rights reserved

ISO 3745:2003(E)
7.4 Auxiliary equipment
Care shall be taken to ensure that air ducts, electrical conduits and piping connected to the source under test
but not part of the typical source configuration, do not radiate a significant amount of sound energy into the
test room.
If practicable, any auxiliary equipment necessary for the operation of the source under test but which is not
part of the source shall be located outside the test room.
7.5 Operation of source under test
During the measurements, the operating conditions specified in the relevant test code, if one exists for the
particular type of machinery and equipment under test, shall be used. If there is no test code, the source shall
be operated, if possible, in a manner which is typical of normal use. In such cases, one or more of the
following operating conditions shall be selected:
 specified load and operating conditions;
 full load (if different from above);
 no load (idling);
 operating conditions corresponding to maximum sound generation representative of normal use;
 simulated load operating under carefully defined conditions;
 operating conditions with a characteristic work cycle.
The sound power level of the source may be determined for any desired set of operating conditions (e.g.
loading, device speed, temperature). These test conditions shall be selected beforehand and shall be held
constant during test. The source shall be in the desired operating condition before any noise measurements
are made.
If the noise emission depends on secondary operating parameters, such as the type of material being
processed or the type of tool being used, as far as is practicable, those parameters shall be selected that give
to the smallest variations and that are typical of the operation. The noise test code for a specific family of
machines shall specify the tool and the material for the test.
For special purposes, it is appropriate to define one or more operating conditions in such a way that the noise
emission of sources of the same family is highly reproducible and that the operating conditions which are most
common and typical for the family of sources are covered. These operating conditions shall be defined in
specific test codes.
If simulated operating conditions are used, they shall be chosen to give sound power levels representative of
normal usage of the source under test.
If appropriate, the results for several separate operating conditions, each lasting for defined periods of time,
shall be combined by energy-averaging to yield the result for a composite overall operating procedure.
The operating conditions of the source during the acoustical measurements shall be fully described in the test
report.
ISO 3745:2003(E)
8 Measurement of sound pressure levels for the determination of sound power
level
8.1 General
An anechoic room provides the preferred environment for measurements with the smallest uncertainty.
However, reasonable accuracy can be obtained in a hemi-anechoic room provided the precautions specified
in this International Standard are observed.
8.2 Measurement surface
8.2.1 Measurement sphere (for measurements in an anechoic room)
For measurements in an anechoic room, the spherical surface at which the sound pressure level is measured
should preferably be centred on the acoustic centre of the sound source. As the location of the acoustic centre
is frequently unknown, the assumed acoustic centre (e.g. the geometric centre of the source) shall be clearly
stated in the test report. The radius of the test sphere shall be equal to or greater than all of the following:
 twice the largest source dimension;
 λ/4 of the lowest frequency of interest; and
 1 m.
No microphone position
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