SIST EN ISO 3741:2010
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)
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)
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.
Akustik - Bestimmung der Schallleistungs- und Schallenergiepegel von Geräusch- quellen aus Schalldruckmessungen - Hallraumverfahren der Genauigkeitsklasse 1 (ISO 3741:2010)
1.1 Allgemeines
Diese Internationale Norm legt Verfahren für die Bestimmung des Schallleistungspegels oder des Schallenergiepegels einer Geräuschquelle aus Schalldruckpegeln fest, die in einem Hallraum gemessen werden. Der von der Geräuschquelle erzeugte Schallleistungspegel (oder der Schallenergiepegel bei Impulsen oder anderen Geräuschen kurzer Dauer) in Frequenzbändern von Terzbreite wird aus diesen Messungen berechnet; hierzu gehören auch alle Korrekturen zur Berücksichtigung jeglicher Unterschiede zwischen den meteorologischen Bedingungen am Ort und während der Zeit der Messung und den meteorologischen Bezugsbedingungen, die einer Bezugskennimpedanz entsprechen. Für zwei Verfahren, ein Direktverfahren und ein Vergleichs¬verfahren, werden Mess- und Rechenschritte für die Bestimmung des Schallleistungspegels und des Schallenergiepegels angegeben.
Im Allgemeinen umfasst der interessierende Frequenzbereich die Terzbänder mit den Mittenfrequenzen von 100 Hz bis 10 000 Hz. Für die Anwendung der festgelegten Verfahren in einem nach tieferen Frequenzen hin erweiterten Frequenzbereich sind Hinweise in Anhang E enthalten. Diese Internationale Norm darf nicht für Frequenzbereiche oberhalb des Terzbandes mit der Mittenfrequenz 10 000 Hz angewendet werden.
ANMERKUNG Für höhere Frequenzen können die in ISO 9295 festgelegten Verfahren angewendet werden.
1.2 Art der Geräusche und Geräuschquellen
Die in dieser Internationalen Norm festgelegten Verfahren sind für alle in ISO 12001 definierten Arten von Geräuschen geeignet (gleichförmige, ungleichförmige, schwankende, Einzel-Schallimpulse, usw.).
Die zu untersuchende Geräuschquelle kann ein Gerät, eine Maschine, Komponente oder Baugruppe sein. Diese Internationale Norm ist anwendbar auf Geräuschquellen mit einem Volumen von nicht mehr als 2 % des Hallraumvolumens. (...)
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)
L'ISO 3741:2010 spécifie des méthodes de détermination du niveau de puissance acoustique ou du niveau d'énergie acoustique émis par une source de bruit à partir des niveaux de pression acoustique mesurés dans une salle d'essai réverbérante. Le niveau de puissance acoustique (ou, dans le cas d'impulsions sonores ou d'émissions sonores transitoires, le niveau d'énergie acoustique) produit par la source de bruit, par bandes de fréquences d'un tiers d'octave, est calculé à l'aide de ces mesures, en incluant les corrections tenant compte de toute différence entre les conditions météorologiques existantes au moment et à l'emplacement où les essais sont réalisés et les conditions correspondant à l'impédance caractéristique de référence. Les méthodes de mesure et de calcul données pour déterminer le niveau de puissance acoustique et le niveau d'énergie acoustique comprennent une méthode directe et une méthode de comparaison.
Le domaine de fréquences représentatif comprend en règle générale les bandes d'un tiers d'octave de fréquences médianes comprises entre 100 Hz et 10 000 Hz. Des lignes directrices, pour l'application des méthodes spécifiées à un domaine de fréquences étendu vers les basses fréquences, sont données dans une annexe. L'ISO 3741:2010 n'est pas applicable au-delà de la bande d'un tiers d'octave centrée sur 10 000 Hz.
Les méthodes spécifiées dans l'ISO 3741:2010 sont applicables à tous les types de bruit (stable, non stable, fluctuant, impulsions acoustiques isolées, etc.) définis dans l'ISO 12001.
La source de bruit en essai peut être un dispositif, une machine, un composant ou un sous-ensemble. L'ISO 3741:2010 est applicable aux sources de bruit dont le volume ne dépasse pas 2 % de celui de la salle d'essai réverbérante. Pour une source dont le volume est supérieur à 2 % de celui de la salle d'essai, il est possible que l'obtention de résultats ayant une classe de précision 1 (classe laboratoire), telle que définie dans l'ISO 12001:1996, ne soit pas réalisable.
Les salles d'essai applicables aux mesurages réalisés conformément à l'ISO 3741:2010 sont les salles d'essai réverbérantes satisfaisant à des exigences spécifiées.
Des informations sont données sur l'incertitude associée aux niveaux de puissance acoustique et aux niveaux d'énergie acoustique déterminés conformément à l'ISO 3741:2010, pour des mesurages effectués dans des bandes de fréquences spécifiques et pour la somme pondérée A de toutes les bandes de fréquences. L'incertitude est conforme à celle de la classe de précision 1 (classe laboratoire) définie dans l'ISO 12001:1996.
Akustika - Določanje ravni zvočnih moči in ravni zvočne energije virov hrupa z zvočnim tlakom - Precizijska metoda za odmevnice (ISO 3741:2010)
Ta mednarodni standard določa metode za določevanje ravni zvočnih moči ali ravni zvočne energije virov hrupa iz ravni zvočnega tlaka, merjenimi v odmevnicah. Raven zvočne moči (ali v primeru prodorov hrupa ali prehodnih emisij hrupa raven zvočne energije), ki jo proizvede vir hrupa v frekvenčnih pasovih širine ene tretjine oktave se izračuna z uporabo teh merjenj, vključno s korekcijami, ki dopuščajo kakršne koli razlike med meteorološkimi pogoji v času in na kraju preskusa in tiste, ki ustrezajo referenčni karakteristični impedanci. Postopki merjenja in izračuna so podani tako za neposredno metodo kot za primerjalno metodo določevanja ravno zvočne moči in ravni zvočne energije. Na splošno frekvenčni razpon, ki nas zanima, vključuje pasove ene tretjine oktave s srednjimi frekvencami od 100 Hz do 10000 Hz. Smernice za uporabo opredeljenih metod pri razširjenemu frekvenčnemu razponu pri nižjih frekvencah so podane v Dodatku E. Ta mednarodni standard ne velja za frekvenčne razpone nad 10000 HZ pasu ene tretjine oktave.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 3741:2010
01-december-2010
1DGRPHãþD
SIST EN ISO 3741:2009
$NXVWLND'RORþDQMHUDYQL]YRþQLKPRþLLQUDYQL]YRþQHHQHUJLMHYLURYKUXSD]
]YRþQLPWODNRP3UHFL]LMVNDPHWRGD]DRGPHYQLFH ,62
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
SIST EN ISO 3741:2010 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 3741:2010
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SIST EN ISO 3741:2010
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.
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SIST EN ISO 3741:2010
EN ISO 3741:2010 (E)
Contents Page
Foreword .3
Annex ZA .4
2
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SIST EN ISO 3741:2010
EN ISO 3741:2010 (E)
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.
3
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SIST EN ISO 3741:2010
EN ISO 3741:2010 (E)
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.
4
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SIST EN ISO 3741:2010
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
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SIST EN ISO 3741:2010
ISO 3741:2010(E)
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ii © ISO 2010 – All rights reserved
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SIST EN ISO 3741:2010
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 2010 – All rights reserved iii
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SIST EN ISO 3741:2010
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
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SIST EN ISO 3741:2010
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 .
© ISO 2010 – All rights reserved v
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SIST EN ISO 3741:2010
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SIST EN ISO 3741:2010
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 2010 – All rights reserved 1
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SIST EN ISO 3741:2010
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
0
2
p
L = 10lg dB (1)
p
2
p
0
where the reference value, p , is 20 µPa
0
[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
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SIST EN ISO 3741:2010
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
0
t
⎡⎤2
1
2
⎢⎥
pt()dt
∫
⎢⎥T
t
⎢⎥1
L = 10 lg dB (2)
pT,
2
⎢⎥
p
0
⎢⎥
⎢⎥
⎢⎥
⎣⎦
where the reference value, p , is 20 µPa
0
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
1
ending at t ) to a reference value, E , expressed in decibels
2 0
t
⎡⎤2
2
⎢⎥
pt()dt
∫
⎢⎥
t
1
⎢⎥
L = 10 lg dB (3)
ET,
⎢⎥
E
0
⎢⎥
⎢⎥
⎢⎥
⎣⎦
2 −10 2
where the reference value, E , is (20 µPa) s = 4 × 10 Pa s
0
T
NOTE 1 This quantity can be obtained by L +10lg dB , where T = 1 s.
pT, 0
T
0
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 2010 – All rights reserved 3
---------------------- Page: 15 ----------------------
SIST EN ISO 3741:2010
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 .
60
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
---------------------- Page: 16 ----------------------
SIST EN ISO 3741:2010
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
1
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 ,
0
expressed in decibels
P
L = 10lg dB (4)
W
P
0
where the reference value, P , is 1 pW
0
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
2
J = Pt()dt (5)
∫
t
1
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 2010 – All rights reserved 5
---------------------- Page: 17 ----------------------
SIST EN ISO 3741:2010
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
0
in decibels
J
L = 10 lg dB (6)
J
J
0
where the reference value, J , is 1 pJ
0
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 purpo
...
SLOVENSKI oSIST prEN ISO 3741:2006
PREDSTANDARD
april 2006
Akustika – Določanje ravni zvočnih moči in ravni zvočne energije virov hrupa
z zvočnim tlakom - Precizijska metoda z merjenjem v odmevnici (ISO/DIS
3741:2006)
Acoustics - Determination of sound power levels and sound energy levels of noise
sources using sound pressure - Precision methods for reverberation test rooms
(ISO/DIS 3741:2006)
ICS 17.140.01 Referenčna številka
oSIST prEN ISO 3741:2006(en)
© Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno
---------------------- Page: 1 ----------------------
EUROPEAN STANDARD
DRAFT
prEN ISO 3741
NORME EUROPÉENNE
EUROPÄISCHE NORM
February 2006
ICS Will supersede EN ISO 3741:1999
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/DIS 3741:2006)
Acoustique - Détermination des niveaux de puissance
acoustique et des niveaux d'énergie acoustique émis par
les sources de bruit à partir de la pression acoustique -
Méthodes de laboratoire en salles d'essais réverbérantes
(ISO/DIS 3741:2006)
This draft European Standard is submitted to CEN members for parallel enquiry. It has been drawn up by the Technical Committee
CEN/TC 211.
If this draft becomes a European Standard, 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.
This draft European Standard was established by CEN 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, 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.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are aware and to
provide supporting documentation.
Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without notice and
shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels
© 2006 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN ISO 3741:2006: E
worldwide for CEN national Members.
---------------------- Page: 2 ----------------------
prEN ISO 3741:2006 (E)
Foreword
This document (prEN ISO 3741:2006) 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 document is currently submitted to the parallel Enquiry.
This document will supersede EN ISO 3741:1999.
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).
Endorsement notice
The text of ISO 3741:2006 has been approved by CEN as prEN ISO 3741:2006 without any
modifications.
2
---------------------- Page: 3 ----------------------
DRAFT INTERNATIONAL STANDARD ISO/DIS 3741
ISO/TC 43/SC 1 Secretariat: DS
Voting begins on: Voting terminates on:
2006-02-23 2006-07-23
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION • МЕЖДУНАРОДНАЯ ОРГАНИЗАЦИЯ ПО СТАНДАРТИЗАЦИИ • ORGANISATION INTERNATIONALE DE NORMALISATION
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 acoustique et des niveaux d'énergie acoustique émis
par les sources de bruit à partir de la pression acoustique — Méthodes de laboratoire en salles d'essais
réverbérantes
[Revision of third edition (ISO 3741:1999) and ISO 3741:1999/Cor1:2001]
ICS 17.140.01
ISO/CEN PARALLEL ENQUIRY
The CEN Secretary-General has advised the ISO Secretary-General that this ISO/DIS covers a subject
of interest to European standardization. In accordance with the ISO-lead mode of collaboration as
defined in the Vienna Agreement, consultation on this ISO/DIS has the same effect for CEN
members as would a CEN enquiry on a draft European Standard. Should this draft be accepted, a
final draft, established on the basis of comments received, will be submitted to a parallel two-month FDIS
vote in ISO and formal vote in CEN.
In accordance with the provisions of Council Resolution 15/1993 this document is circulated in
the English language only.
Conformément aux dispositions de la Résolution du Conseil 15/1993, ce document est distribué
en version anglaise seulement.
To expedite distribution, this document is circulated as received from the committee secretariat.
ISO Central Secretariat work of editing and text composition will be undertaken at publication
stage.
Pour accélérer la distribution, le présent document est distribué tel qu'il est parvenu du
secrétariat du comité. Le travail de rédaction et de composition de texte sera effectué au
Secrétariat central de l'ISO au stade de publication.
THIS DOCUMENT IS A DRAFT CIRCULATED FOR COMMENT AND APPROVAL. IT IS THEREFORE SUBJECT TO CHANGE AND MAY NOT BE
REFERRED TO AS AN INTERNATIONAL STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS BEING ACCEPTABLE FOR INDUSTRIAL, TECHNOLOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN NATIONAL REGULATIONS.
© International Organization for Standardization, 2006
---------------------- Page: 4 ----------------------
ISO/DIS 3741
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©
ii ISO 2006 – All rights reserved
---------------------- Page: 5 ----------------------
ISO/DIS 3741
Contents Page
Foreword .v
Introduction.vi
1 Scope.1
1.1 General .1
1.2 Types of noise and noise sources.1
1.3 Reverberation test room.1
1.4 Measurement uncertainty.1
2 Normative references.2
3 Terms and definitions .2
4 Reference meteorological conditions .5
5 Reverberation test room.5
5.1 General .5
5.2 Volume and shape of test room.5
5.3 Sound absorption of test room.6
5.4 Criterion for background noise.6
5.5 Atmospheric temperature, humidity and pressure.8
6 Instrumentation and measurement equipment .8
6.1 General .8
6.2 Calibration.9
7 Definition, location, installation and operation of noise source under test.9
7.1 General .9
7.2 Auxiliary equipment .9
7.3 Noise source location .9
7.4 Installation and mounting conditions .10
7.5 Operation of source during test.10
8 Measurements in the reverberation test room .11
8.1 General .11
8.2 Initial location of the noise source under test.11
8.3 Microphone positions .11
8.4 Measurement of sound pressure levels.12
8.5 Measurement of sound energy levels .15
8.6 Measurement of sound pressure levels from the reference sound source for the
comparison method .16
8.7 Measurement of reverberation time .16
8.8 Measurement of meteorological conditions.16
9 Determination of sound power levels and sound energy levels .17
9.1 Sound power levels of noise sources.17
9.2 Sound energy levels for a noise source .21
9.3 A-weighted sound power level and sound energy level .24
10 Measurement uncertainty.24
11 Information to be recorded.26
11.1 General .26
11.2 Noise source under test.26
11.3 Test environment.26
11.4 Instrumentation and measurement equipment .26
11.5 Acoustical data.26
© ISO 2005 – All rights reserved iii
DRAFT 2006
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ISO/DIS 3741
12 Information to be reported. 27
Annex A (informative) Guidelines for the design of reverberation test rooms. 28
Annex B (informative) Guidelines for the design of rotating diffusing vanes . 30
Annex C (normative) Reverberation test room qualification procedure for the measurement of
broad-band sound . 31
Annex D (normative) Reverberation test room qualification procedure for the measurement of
discrete-frequency components . 33
Annex E (informative) Extension of frequency range to frequencies below 100 Hz . 38
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. 39
Annex G (informative) Guidance on the development of information on measurement uncertainty . 42
Bibliography. 49
iv © ISO 2005 – All rights reserved
DRAFT 2006
---------------------- Page: 7 ----------------------
ISO/DIS 3741
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.
© ISO 2005 – All rights reserved v
DRAFT 2006
---------------------- Page: 8 ----------------------
ISO/DIS 3741
Introduction
0.1 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 will depend on the purpose of the test to determine the sound power level or sound
energy level and on the facilities available. General guidelines to assist in the selection are provided in
1)
ISO 3740 . The series of standards of which this International Standard is a part gives 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 on mounting, loading and operating conditions under which the sound power levels or sound
energy levels are to be obtained.
0.2 The methods given in this International Standard require the source 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 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:
the space/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/time averaged mean-
square pressure throughout the room;
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 and set-up 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.
0.3 The methods given 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 and data with
frequency weighting ‘A’ can be computed.
0.4 This International Standard describes methods giving a precision grade of accuracy (grade 1) 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 acceptable, reference can be made to ISO 3743-1, ISO 3743-2 or ISO 3747.
0.5 This International Standard cancels and replaces ISO 3741:1999.
1) Under revision
vi © ISO 2005 – All rights reserved
DRAFT 2006
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DRAFT INTERNATIONAL STANDARD ISO/DIS 3741
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 requirements for which
are stated, from that noise source (machinery or equipment) located in the 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 midband 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. For higher frequencies, the use of methods
given in ISO 9295 is recommended.
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 may 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 might not be possible
to achieve accuracy grade 1 in the results.
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 limited bands of frequency and for
calculations from those measurements with frequency weighting A applied. The uncertainty conforms with that
of the precision grade of accuracy (grade 1) defined in ISO 12001.
© ISO 2005 – All rights reserved 1
DRAFT 2006
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ISO/DIS 3741
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, Acoustics – Measurement of the reverberation time of rooms with reference to other acoustical
parameters
ISO 6926, Acoustics – Requirements for the performance and calibration of reference sound sources for the
determination of sound power levels
ISO 7574-1, Acoustics – Statistical methods for determining and verifying stated noise emission values of
machinery and equipment – Part 1: General considerations and definitions
ISO 12001, Acoustics – Noise emitted by machinery and equipment – Rules for the drafting and presentation
of a noise test code
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
Guide to the expression of uncertainty in measurement (GUM). International Organization for Standardization,
Geneva, Switzerland. ISBN 92-67-10188-9, First Edition 1993, corrected and reprinted 1995
3 Terms and definitions
For the purposes of this International Standard, the following definitions apply:
3.1
sound pressure
p
fluctuating pressure superimposed on the static pressure by the presence of sound, 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
0
2
p
L = 10lg dB (1)
p
2
p
0
–5
The reference value, p , is 20 µPa (2 x 10 Pa).
0
3.3
time-averaged sound pressure level
L
p,T
level of the time-averaged square of the sound pressure over the measurement time interval T = t – t ,
2 1
expressed in decibels
2 © ISO 2005 – All rights reserved
DRAFT 2006
---------------------- Page: 11 ----------------------
ISO/DIS 3741
t
2 2
1 p (t)
= 10lg dt (2)
L
p,T
∫
2
T
p
t
0
1
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 .
A
p
3.4
single-event sound pressure level
L
E
level of the time-integrated square of the sound pressure of an isolated single sound event (burst of sound or
transient sound) of specified duration T (or specified measurement time interval T = t – t covering the single
2 1
event) normalized to reference time interval T = 1 s, expressed in decibels
0
t
2
2
1 p (t) T
L = 10lg dt dB = L + 10lg dB (3)
E p,T
∫
2
T T
p
0 0
t 0
1
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, expressed in seconds
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
rev
time that would be required for the sound pressure level to decrease by 60 dB after a sound source in space
has stopped instantaneously, expressed in seconds
NOTE The reverberation time is frequency dependent.
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 use in this International Standard, sound absorption coefficients are calculated in accordance with
ISO 354.
3.10
equivalent sound absorption area
A
product of the area and sound absorption coefficient of a surface, expressed in square metres
© ISO 2005 – All rights reserved 3
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ISO/DIS 3741
3.11
reference sound source
sound source meeting the requirements of ISO 6926
3.12
frequency range of interest
for general purposes, the range of one-third-octave bands with nominal midband frequencies from 100 Hz to
10 000 Hz
NOTE For special purposes, the range may be extended or reduced, provided that the test environment and
instrumentation otherwise meet all requirements of this International Standard. The range may be extended downwards in
frequency as far as the 50 Hz one-third-octave band (see Annex E), but may not be extended upwards beyond the
10 000 Hz band. For reduced frequency ranges, the report shall clearly state the reduced range and shall indicate that the
reported results are in conformance with this International Standard over the reduced frequency range.
3.13
background noise
noise from all sources other than the noise source under test
NOTE Background noise may inclu
...
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