EN ISO 3746:1995

SLOVENSKI STANDARD
SIST EN ISO 3746:1997
01-april-1997
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Acoustics - Determination of sound power levels of noise sources using sound pressure -
Survey method using an enveloping measurement surface over a reflecting plane (ISO
3746:1995)
Akustik - Bestimmung der Schalleistungspegel von Geräuschquellen aus
Schalldruckmessungen - Hüllflächenverfahren der Genauigkeitsklasse 3 über einer
reflektierenden Ebene (ISO 3746:1995)
Acoustique - Détermination des niveaux de puissance acoustique émis par les sources
de bruit a partir de la pression acoustique - Méthode de contrôle employant une surface
de mesure enveloppante au-dessus d'un plan réfléchissant (ISO 3746:1995)
Ta slovenski standard je istoveten z: EN ISO 3746:1995
ICS:
17.140.01 $NXVWLþQDPHUMHQMDLQ Acoustic measurements and
EODåHQMHKUXSDQDVSORãQR noise abatement in general
SIST EN ISO 3746:1997 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 3746:1997

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SIST EN ISO 3746:1997

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SIST EN ISO 3746:1997

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SIST EN ISO 3746:1997
INTERNATIONAL
STANDARD
Second edition
1995-08-I 5
Acoustics - Determination of sound
power levels of noise sources using sound
pressure - Survey method using an
enveloping measurement surface over a
reflecting plane
- Dgtermination des niveaux de puissance acoustique 6mis
Acoustique
par /es sources de bruit ;i paflir de la pression acoustique - Mkthode de
contr6le employant une surface de mesure enveloppante au-dessus d’un
plan r6fkhissant
Reference number
IS0 3746: 1995(E)

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SIST EN ISO 3746:1997
IS0 3746: 1995(E)
Contents
Page
.............................................................................................. 1
1 Scope
..................................................................... 3
2 Normative references
3
3 Definitions .
4
4 Acoustic environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
5 Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
6 Installation and operation of source under test . . . . . . . . . . . . . . . . . . . . . . . .
7
7 Measurement of sound pressure levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8 Calculation of A-weighted surface sound pressure level and
10
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A-weighted sound power level
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9 Information to be recorded
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
10 Information to be reported
Annexes
. . , . . . . . 14
A Qualification procedures for the acoustic environment
17
B Microphone array on the hemispherical measurement surface
21
C Microphone array on the parallelepiped measurement surface
. . . . . . . . . . . . . . . . . . . . 26
D Guidelines for the detection of impulsive noise
27
E Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
0 IS0 1995
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-1211 Gen&e 20 l Switzerland
Printed in Switzerland
ii

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SIST EN ISO 3746:1997
0 IS0
IS0 3746: 1995(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide ’
federation of national standards bodies (IS0 member bodies). The work
of preparing International Standards is normally carried out through IS0
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. IS0
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
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.
International Standard IS0 3746 was prepared by Technical Committee
lSO/TC 43, Acoustics, Subcommittee SC 1, Noise.
This second edition cancels and replaces the first edition
(IS0 3746:1979), which has been technically revised.
Annexes A, B and C form an integral part of this International Standard.
Annexes D and E are for information only.

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SIST EN ISO 3746:1997
0 IS0
IS0 3746:1995(E)
Introduction
0.1 This International Standard’ is one of the IS0 3740 series, which
specifies various methods for determining the sound power levels of ma-
chines, equipment and their sub-assemblies. When selecting one of the
methods of the IS0 3740 series, it is necessary to select the most ap-
propriate for the conditions and purposes of the noise test. General
guidelines to assist in the selection are provided in IS0 3740. The
IS0 3740 series gives only general principles regarding the operating and
mounting conditions of the machine or equipment under test. Reference
should be made to the test code for a specific type of machine or equip-
ment, if available, for specifications on mounting and operating conditions.
0.2 This International Standard specifies a method for measuring the
sound pressure levels on a measurement surface enveloping the source
and for calculating the sound power level produced by the source. The
enveloping surface method can be used for any of three grades of accu-
racy (see tableO.l), and is used in this International Standard for grade 3
accuracy.
The use of this International Standard requires certain qualification criteria
to be fulfilled as described in table 0.1. If the relevant qualification criteria
cannot be met, it might be possible to use IS0 3747 or IS0 9614.
Noise test codes for specific families of machines or equipment should
be based without any contradiction on the requirements of one or more
of the basic documents of the IS0 3740 or IS0 9614 series.
If measurements are made in typical machine rooms, where sources are
normally installed, corrections may be required to account for background
noise or undesired reflections.
The methods specified in this International Standard permit the determi-
nation of sound power level as an A-weighted value directly from the A-
weighted sound pressure level measurements.
0.3 In this International Standard, the computation of sound power level
from sound pressure level measurements is based on the premise that the
sound power output of the source is directly proportional to the mean-
square sound pressure averaged in time and space.

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SIST EN ISO 3746:1997
0 IS0
IS0 3746:1995(E)
Table 0.1 - Overview of International Standards for determination
of sound power levels of noise sources using enveloping surface
methods over a reflecting plane and giving different grades of
accuracy
IS0 3745 IS0 3744
IS0 3746
Precision Engineering
Survey method
Parameter
method method
Grade 1 Grade 2 Grade 3
Test environment Hemi-anechoic Outdoors or indoors Outdoors or in-
room doors
Criterion for suitability
K2< 0,5 dB K&2 dB K2<7 dB
of test environmentl)
Volume of sound Preferably less No restriction: lim- No restriction: lim-
source ited only by avail-
than 0,5 % of ited only by avail-
test room able test able test
volume environment environment
Character of noise Any (broad-band, narrow-band, discrete-frequency, steady, non-
steady, impulsive)
Limitation for back- AL> lOdB(if AL,> 6 dB (if poss- ti>3dB
ground noise’) possible, ex- i ble, exceeding
ceeding 15 dB) 15 dB)
K,< 0,4 dB K,< I,3 dB K,<3dB
Number of measure-
2 10 > 92) 3 42)
ment points
Instrumentation:
a) Sound level meter a) type 1 as a) type 1 as a) type 2 as
at least complying specified in
specified in specified in
with IEC 651 IEC 651
IEC 651
b) Integrating sound b) type 1 as b) type 1 as b) type 2 as
level meter at specified in specified in specified in
least complying IEC 804 IEC 804
IEC 804
with
c) Frequency band c) class 1 as c) class 1 as
filter set at least specified in specified in
complying with IEC 1260 IEC 1260
Precision of method
aR< 1 dB a*< I,5 dB aR< 3 dB (if
for determining &,*
K2 < 5 dB)
expressed as standard
aR\< 4 dB (if
deviation of repro-
5 dB< K2< 7 dB)
ducibility
If discrete tones
are predominant,
the value of bR is
1 dB greater
I) The values of K, and K2 given shall be met in each frequency band within the fre-
quency range of interest for determining the sound power spectrum. For determining
A-weighted sound power levels, the same criteria apply to K,* and Ku.
2) Under given circumstances, it is permissible to use a reduced number of microphone
positions.

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SIST EN ISO 3746:1997
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SIST EN ISO 3746:1997
INTERNATIONAL STANDARD 0 IS0 IS0 3746: 1995(E)
Acoustics - Determination of sound power levels of
noise sources using sound pressure - Survey method
using an enveloping measurement surface over a
reflecting plane
This International Standard is applicable to noise
1 Scope
sources of any type and size (e.g. device, machine,
component, sub-assembly).
1.1 General
NOTE 3 Measurements according to this International
This International Standard specifies a method for
Standard may be impracticable for very tall or very long
measuring the sound pressure levels on a measure-
sources such as chimneys, ducts, conveyors and multi-
ment surface enveloping the source in order to cal-
source industrial plants.
culate the sound power level produced by the noise
source. It gives requirements for the test environment
1.3 Test environment
and instrumentation as well as techniques for obtain-
ing the surface sound pressure level from which the
The test environment that is applicable for measure-
sound power level of the source is calculated, leading
ments made in accordance with this International
to results which have a grade 3 accuracy.
Standard may be located indoors or outdoors, with
one or more reflecting planes present, meeting
It is important that specific noise test codes for vari-
specified requirements.
ous types of equipment be established and used in
accordance with this International Standard. For each
type of equipment, such noise test codes will give
1.4 Measurement uncertainty
detailed requirements on mounting, loading and op-
erating conditions for the equipment under test as
For sources which radiate steady broad-band noise,
well as a selection of the measurement surface and
determinations made in accordance with this Inter-
the microphone array as specified in this International
national Standard result, with few exceptions, in
Standard.
standard deviations of reproducibility of the A-
weighted sound power level equal to or less than
NOTE 1 The noise test code for a particular type of
3 dB (if KzA determined in accordance with annex A
equipment should give detailed information on the particular
is lower than 5 dB) or 4 dB (if KzA is within the range
surface that is selected, as the use of differently shaped
measurement surfaces may yield differing estimates of the of 5 dB to 7 dB). For discrete-tone sources, the stan-
sound power level of a source.
dard deviation of reproducibility is normally 1 dB
greater (see table 1).
1.2 Types of noise and noise sources
A single value of the sound power level of a noise
source determined in accordance with the procedures
The method specified in this International Standard is
given in this International Standard is likely to differ
suitable for measurements of all types of noise.
from the true value by an amount within the range of
the measurement uncertainty. The uncertainty in de-
NOTE 2 A classification of different types of noise
(steady, non-steady, quasi-steady, impulsive, etc.) is given terminations of the sound power level arises from
in IS0 12001 e
several factors which affect the results, some associ-
1

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SIST EN ISO 3746:1997
5 A noise test code for a particular family of sound sources
ated with environmental conditions at the test site
may have lower values of the standard deviation of repro-
and others with experimental techniques.
ducibility (see note 8).
If a particular noise source were to be transported to
6 The standard deviations listed in table 1 are associated
each of a number of different test sites, and if, at each
with the test conditions and procedures defined in this
test site, the sound power level of that source were
International Standard and not with the noise source itself.
to be determined in accordance with this International
They arise in part from variations between test sites,
Standard, the results would show a scatter. The changes in atmospheric conditions if outdoors, the ge-
ometry of the test room or outdoor environment, the
standard deviation of the measured levels could be
acoustical properties of the reflecting plane, absorption at
calculated (see examples in IS0 7574-4:1985, annex
the test room boundaries if indoors, background noise, and
B). With few exceptions, these standard deviations
the type and calibration of instrumentation. They are also
would not exceed those listed in table 1. The values
due to variations in experimental techniques, including the
given in table 1 are standard deviations of repro-
size and shape of the measurement surface, number and
ducibility, OR, are defined in IS0 7574-l. The values
location of microphone positions, sound source location, in-
of table 1 take into account the cumulative effects of
tegration times, and determination of environmental cor-
measurement uncertainty in applying the procedures
rections, if any. The standard deviations are also affected
of this International Standard, but exclude variations
by errors associated with measurements taken in the near
field of the source; such errors depend upon the nature of
in the sound power output caused by changes in op-
the sound source, but generally increase for smaller meas-
erating conditions (e.g. rotational speed, line voltage)
urement distances and lower frequencies (below 250 Hz).
or mounting conditions.
7 If measurements are made at several test sites, the re-
The measurement uncertainty depends on the stan-
sults of sound power determinations on a given source may
dard deviation of reproducibility tabulated in table 1
be in better agreement than would be implied by the stan-
and on the degree of confidence that is desired. As
dard deviations of table 1.
examples, for a normal distribution of sound power
8 For a particular family of sound sources, a similar size
levels, there is a 90 % confidence that the expected
with similar sound power spectra and similar operating
value of the sound power level of a source lies within
conditions, the standard deviations of reproducibility may
the range + 1,6560, of the measured value and a
be smaller than the values given in table 1. Hence, a noise
95 % confidence that it lies within the range
test code for a particular type of machinery or equipment
+ 1,960~ of the measured value. For further exam-
making reference to this International Standard may state
ples, reference should be made to the IS0 7574 se-
standard deviations smaller than those listed in table 1, if
ries and IS0 9296.
substantiation is available from the result of suitable inter-
laboratory tests.
9 The standard deviations of reproducibility, as tabulated
in table 1, include the uncertainty associated with repeated
measurements on the same noise under the same con-
Table 1 - Estimated upper values of the
ditions (standard deviation of repeatability, see IS0 7574-l).
standard deviations of reproducibility of
This uncertainty is usually much smaller than the uncertainty
A-weighted sound power levels determined in
associated with variability from one test site to another.
accordance with this International Standard
However, if it is difficult to maintain stable operating or
mounting conditions for a particular source, the standard
Highest standard
deviation of repeatability may not be small compared with
Application deviation of
the values given in table 1. In such cases, the fact that it
reproducibility, OR
was difficult to obtain repeatable sound power level data on
dB
the source should be recorded and stated in the test report.
For a source which emits noise
IO The procedures of this International Standard and the
with a relatively “flat” spectrum
standard deviations given in table 1 are applicable to meas-
3
over the frequency range of
urements on an individual machine. Characterization of the
interest
sound power levels of batches of machines of the same
family or type involves the use of random sampling tech-
For a source which emits noise
niques in which confidence intervals are specified, and the
that contains predominant dis- 4
results are expressed in terms of statistical upper limits. In
Crete tones
applying these techniques, the total standard deviation must
be known or estimated, including the standard deviation of
production, as defined in IS0 7574-1, which is a measure
NOTES
of the variation in sound power output between individual
4 lf KZA is greater than or equal to 5 dB, bR may be 1 dB
machines within the batch. Statistical methods for the
greater than the values given in table 1.

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SIST EN ISO 3746:1997
IS0 3746:1995(E)
0 IS0
characterization of batches of machines are described in I EC 804: 1985, Integrating-averaging sound level
IS0 7574-4.
meters, and Amendment I:1989 and Amendment
2:1993.
I EC 942: 1988, Sound calibrators.
2 Normative references
3 Definitions
The following standards contain provisions which,
For the purposes of this International Standard, the
through reference in this text, constitute provisions
following definitions apply.
of this International Standard. At the time of publi-
cation, the editions indicated were valid. All standards
3.1 sound pressure, p: A fluctuating pressure
are subject to revision, and parties to agreements
superimposed on the static pressure by the presence
based on this International Standard are encouraged
of sound. It is expressed in pascals.
to investigate the possibility of applying the most re-
cent editions of the standards indicated below.
NOTE I I The magnitude of the sound pressure can be
Members of IEC and IS0 maintain registers of cur-
expressed in several ways, such as instantaneous sound
rently valid International Standards. pressure, maximum sound pressure, or as the square root
of the mean-square sound pressure over designated time
and space (i.e. over the measurement surface).
- Measurement of sound
IS0 354: 1985, Acoustics
absorption in a reverberation room.
3.2 sound pressure level, Lp: Ten times the log-
arithm to the base 10 of the ratio of the square of the
IS0 3744:1994, Acoustics - Determination of sound
sound pressure to the square of the reference sound
power levels of noise sources using sound pressure
pressure. Sound pressure levels are expressed in
- Engineering method in an essentially free field over
decibels.
a reflecting plane.
The frequency weighting or the width of the fre-
IS0 3745:1977, Acoustics - Determination of sound
quency band used and the time weighting (S, F, or I,
power levels of noise sources - Precision methods
see IEC 651) shall be indicated. The reference sound
for anechoic and semi-anechoic rooms.
pressure is 20 PPa (2 x 10m5 Pa).
- Determination of sound
IS0 374711987, Acoustics
NOTE 12 For example, the A-weighted sound pressure
power levels of noise sources - Survey method us-
level with time weighting S is LpAs.
ing a reference sound source.
3.2.1 time-averaged sound pressure level, Lpeq +
IS0 4871: -I), Acoustics - Declaration and verifica-
Sound pressure level of a continuous steady sound
tion of noise emission values of machinery and
that, within a measurement time interval T, has the
equipment.
same mean-square sound pressure as a sound under
consideration which varies with time:
IS0 6926: 1990, Acoustics - Determination of sound
power levels of noise sources - Requirements for
the performance and calibration of reference sound
Lpeq,T= 10 Ig [ $I,TIO”~lLp(‘) dt] dB
sources.
IS0 7574-l :I 985, Acoustics - Statistical methods for
= IO Ig . . .
[+-j;y dr] dB
(1)
determining and verifying stated noise emission
values of machinery and equipment - Part 1: Gen-
eral considerations and definitions.
Time-averaged sound pressure levels are expressed
in decibels and shall be measured with an instrument
IS0 7574-411985, Acoustics - Statistical methods for
which complies with the requirements of IEC 804.
determining and verifying stated noise emission
values of machinery and equipment - Part 4:
NOTES
Methods for stated values for batches of machines.
13 Time-averaged sound pressure levels are usually A-
IEC 651 :I 979, Sound level meters, and Amendment
weighted and denoted by LpAeq,T which is usually abbrevi-
1 :I 993. ated to LpA.
1) To be published. (Revision of IS0 4871 :I 984)

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SIST EN ISO 3746:1997
Q IS0
IS0 3746:1995(E)
14 In general, the subscripts “eq” and “T” are omitted
closes the source and terminates on the reflecting
since time-averaged sound pressure levels are necessarily
plane or planes.
determined over a certain measurement time interval.
3.9 characteristic source dimension, d,: Half the
3.2.2 single-event sound pressure level, LP ,+
length of the diagonal of the box consisting of the
Time-integrated sound pressure level of an isolated
reference box and its images in adjoining reflecting
single sound event of specified duration T (or speci-
planes.
fied measurement time T) normalized to To = 1 s. It is
expressed in decibels and is given by the following 3.10 measurement distance, d: The distance from
formula: the reference box to a box-shaped measurement sur-
face.
LP,,s=lOlg[+-/;+ di] dB
3.11 measurement r: The radius of a
hemispherical measurement surface.
=L,,,,+ 10 lgz dB . . .
(2)
,
3.12 background noise: Noise from all sources
TO
other than the source under test.
3.2.3 measurement time interval: A portion or a
NOTE 16 Background noise may include contributions
multiple of an operational period or operational cycle
from airborne sound, structure-borne vibration, and elec-
for which the time-averaged sound pressure level is
trical noise in instrumentation.
determined.
3.13 background noise correction, K,: A correction
3.3 measurement surface: A hypothetical surface
term to account for the influence of background noise
of area S, enveloping the source on which the meas-
on the surface sound pressure level; K, is frequency
urement points are located. The measurement sur-
dependent and is expressed in decibels. The cor-
face terminates on one or more reflecting planes.
rection in the case of A-weighting is denoted K,*.
3.14 environmental correction, K2: A correction
3.4 surface sound pressure level, LT: The energy-
term to account for the influence of reflected or ab-
average of the time-averaged sound pressure levels
sorbed sound on the surface sound pressure level;
at all the microphone positions on the measurement
K2 is frequency dependent and is expressed in deci-
surface, with the background noise correction K,
bels. The correction in the case of A-weighting is de-
(3.13) and the environmental correction K2 (3.14) ap-
noted KzA.
plied. It is expressed in decibels.
3.15 impulsive noise index (impulsiveness): A
3.5 sound power, W: The rate per unit time at
quantity by means of which the noise emitted by a
which airborne sound energy is radiated by a source.
source can be characterized as “impulsive”. (See an-
It is expressed in watts. .
nex D.) It is expressed in decibels.
36 . sound power level, &,: Ten times the logarithm
to the base 10 of the ratio of the sound power radi-
4 Acoustic environment
ated by the sound source under test to the reference
sound power. It is expressed in decibels.
4.1 General
The frequency weighting or the width of the fre-
Test environments that are suitable for measure-
quency band used shall be indicated. The reference
ments in accordance with this International Standard
sound power is 1 pW (IO- ‘* W).
include a flat outdoor area or a room which meets the
qualification requirements of 4.2 and which is ade-
NOTE 15 For example, the A-weighted sound power
quately isolated from background noise in accordance
level is &A.
with the requirements of 4.3.
3.7 frequency range of interest: For general pur-
poses, the frequency range of interest includes the
Criterion for adequacy of the test
4.2
octave bands with centre frequencies from 25 Hz to
environment
8 000 Hz.
Annex A describes procedures for determining the
3.8 reference box: A hypothetical surface which is magnitude of the environmental correction K2*, to ac-
the smallest rectangular parallelepiped that just en- count for deviations of the test environment from the

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SIST EN ISO 3746:1997
0 IS0 IS0 3746:1995(E)
ideal condition. For this International Standard, the
Installation and operation of source
6
environmental correction K2A (see table0.1 and 8.3)
under test
shall be numerically less than or equal to 7 dB.
6.1 General
NOTE 17 If the environmental correction KzA exceeds
7 dB, it is recommended that either a reference sound
source method (IS0 3747) or the method of IS0 9614 be The manner in which the source under test is installed
used.
and operated may have a significant influence on the
sound power emitted by the source. This clause
specifies conditions that minimize variations in the
4.3 Criterion for background noise sound power output due to installation and operating
conditions of the source under test. The instructions
Averaged over the microphone positions, the A-
of a noise test code, if any exists, shall be followed in
weighted sound pressure level of the background
so far as installation and operation of the source under
noise shall be at least 3 dB below the sound pressure
test is concerned.
level to be measured (see table 0.1 and 8.2).
Particularly for large sources, it is important that a
noise test code specify which components, sub-
assemblies, auxiliary equipment, power sources, etc.
5 Instrumentation
are to be included in the reference box.
6.2 Source location
5. I General
The source to be tested shall be installed with respect
The instrumentation system, including the micro-
to the reflecting plane or planes in one or more lo-
phones and cables, shall meet the requirements for
cations as if it were being installed for normal usage.
a type 2 instrument specified in IEC 651 or, in the
If several possibilities exist, or if typical installation
case of integrating-averaging sound level meters, the
conditions are unknown, special arrangements shall
requirements for a type 2 instrument specified in
be made and described in the test report. If the lo-
IEC 804.
cation of the source within the test environment can
be selected, sufficient space shall be allowed so that
the measurement surface can develop the source
5.2 Calibration
under test in accordance with the requirements of
71 . .
During each series of measurements, a sound
calibrator with an accuracy of + 0,3 dB (class 1 as
specified in IEC 942) shall be applied to the micro- 6.3 Source mounting
phone to verify the calibration of the entire measuring
In many cases, the sound power emitted will depend
system at one or more frequencies over the fre-
upon the support or mounting conditions of the
quency range of interest.
source under test. Whenever a typical condition of
The compliance of the calibrator shall be verified with
mounting exists for the equipment under test, that
the requirements of IEC 942 once a year and the
condition shall be used or simulated, if feasible.
compliance of the instrumentation system with the
If a typical condition of mounting does not exist or
requirements of IEC 651 (and IEC 804 in the case of
cannot be utilized for the test, care shall be taken to
integrating systems) at least every 2 years in a labor-
avoid changes in the soun
...