EN ISO 354:2003

Acoustics - Measurement of sound absorption in a reverberation room (ISO 354:2003)

ISO 354:2003 specifies a method of measuring the sound absorption coefficient of acoustical materials used as wall or ceiling treatments, or the equivalent sound absorption area of objects, such as furniture, persons or space absorbers, in a reverberation room. It is not intended to be used for measuring the absorption characteristics of weakly damped resonators.
The results obtained can be used for comparison purposes and for design calculation with respect to room acoustics and noise control.

Akustik - Messung der Schallabsorption in Hallräumen (ISO 354:2003)

Diese Internationale Norm beschreibt ein Hallraum-Verfahren zur Messung des Schallabsorptionsgrades von akustischen Materialien, die zur Bekleidung von Wänden und Decken benutzt werden, oder der äquivalenten Schallabsorptionsfläche von Einzelobjekten, wie Möbelstücken, Personen oder Absorptionskörpern. Das Verfahren ist nicht für die Messung der Absorptionseigenschaften schwach gedämpfter Resonatoren vorgesehen.
Die erhaltenen Ergebnisse können zu Vergleichszwecken und für Entwurfsberechnungen in der Raumakustik und der Lärmbekämpfung verwendet werden.

Acoustique - Mesurage de l'absorption acoustique en salle réverbérante (ISO 354:2003)

L'ISO 354:2003 spécifie une méthode de mesurage en salle réverbérante du coefficient d'absorption acoustique de matériaux acoustiques utilisés pour le traitement de murs ou de plafonds, ou de la surface d'absorption acoustique équivalente d'objets distincts tels que meubles, personnes ou matériaux absorbants. Elle n'est pas destinée a être employée pour le mesurage des caractéristiques d'absorption de résonateurs faiblement amortis.
Les résultats obtenus peuvent être utilisés pour effectuer des comparaisons et des calculs dans le domaine de l'acoustique des salles et du contrôle du bruit.

Akustika - Merjenje absorpcije zvoka v odmevnici - (ISO 354:2003)

General Information

• Status: Published
• Publication Date: 14-May-2003
• ICS: 17.140.01 - Acoustic measurements and noise abatement in general
• ICS: 91.120.20 - Acoustics in building. Sound insulation
• Technical Committee: CEN/TC 126 - Acoustic properties of building products and of buildings
• Drafting Committee: CEN/TC 126/WG 1 - Methods for measuring the sound insulation of building elements and the acoustic performances of buildings
• Current Stage: 9092 - Decision on results of review/2YR ENQ - revise - Review Enquiry
• Start Date: 11-Jun-2008
• Completion Date: 11-Jun-2008
• Directive: 305/2011 - Regulation (eu) No 305/2011 of the European Parliament and of the Council of 9 march 2011 laying down harmonised conditions for the marketing of construction products and repealing council directive 89/106/eec
• Directive: 89/106/EEC - Construction products
• Mandate: M/111 - Mandate to CEN/CENELEC concerning the execution of standardization work for harmonized standards on circulation fixtures
• Mandate: M/121 - Mandate to CEN/CENELEC concerning the execution of standardization work for harmonized standards on internal and external wall and ceiling finishes
• Ref Project: SIST EN ISO 354:2004 - Acoustics - Measurement of sound absorption in a reverberation room (ISO 354:2003)

Relations

• Replaces: EN ISO 354:1993 - Acoustics - Measurement of sound absorption in a reverberation room (ISO 354:1985)
• Effective Date: 22-Dec-2008
• Replaces: EN ISO 354:1993/A1:1997 - Acoustics - Measurement of sound absorption in a reverberation room - Amendment 1: Test specimen mountings for sound absorption tests (ISO 354:1985/AMD1:1997)
• Effective Date: 22-Dec-2008

Overview

EN ISO 354:2003 - Acoustics: Measurement of sound absorption in a reverberation room (ISO 354:2003) specifies a standardized method for measuring the sound absorption coefficient of acoustic materials (wall/ceiling treatments) or the equivalent sound absorption area of objects (furniture, people, space absorbers) using a reverberation room. Results are intended for comparison, product characterization and for use in room acoustics and noise control design calculations. The standard is not intended for measuring weakly damped resonators.

Key topics and technical requirements

• Measurement principle: Determine average reverberation time (T) in a reverberation room with and without the test specimen and compute the specimen’s equivalent absorption using Sabine’s equation.
• Sound field requirements: Tests assume a diffuse sound field approximated in a properly designed reverberation room (see Annex A).
• Measurement methods:
  • Interrupted noise method (direct decay recording)
  • Integrated impulse response method (reverse-time integration of impulse responses)
• Frequency range: Measurements in one‑third‑octave bands with centre frequencies from 100 Hz to 5 000 Hz (ISO 266 preferred frequencies).
• Terms and results: Defines decay curves, reverberation time (T), equivalent sound absorption area (A) and sound absorption coefficient (αs). Note: αs from reverberation measurements can exceed 1.0 (diffraction effects).
• Test arrangement and specimen mounting: Requirements for reverberation room layout, diffusion of sound field and defined specimen mounting types (including updates from previous edition such as Type B and Type J).
• Environmental and procedural controls: Specifies temperature/relative-humidity considerations and measurement precision (see sections on measurement of reverberation time, precision and presentation of results).
• Reporting: Prescribed content for a standardized test report.

Applications and who uses it

• Acoustic test laboratories performing standardized absorption measurements.
• Manufacturers of acoustic panels, ceiling tiles, room absorbers and furniture seeking product performance data.
• Acoustic consultants, architects and building designers using absorption data for room acoustics design, speech intelligibility, HVAC noise control and interior acoustic treatment calculations.
• Researchers comparing materials or validating modelling approaches.

Practical uses include performance comparison of absorptive treatments, specifying materials for auditoria/office spaces, and generating input data for acoustic simulation and noise-control calculations.

Related standards

• ISO 266 - Preferred frequencies (used for octave/third-octave band centres)
• ISO 9613-1 - Attenuation of sound outdoors (atmospheric absorption)
• IEC 61260 - Octave-band and fractional-octave-band filters

Keywords: EN ISO 354:2003, sound absorption, reverberation room, reverberation time, sound absorption coefficient, room acoustics, acoustic measurements, noise control.

Standards Content (Sample)

SLOVENSKI STANDARD
01-januar-2004
1DGRPHãþD
SIST EN 20354:1998
SIST EN 20354:1998/A1:1998
Akustika - Merjenje absorpcije zvoka v odmevnici - (ISO 354:2003)
Acoustics - Measurement of sound absorption in a reverberation room (ISO 354:2003)
Akustik - Messung der Schallabsorption in Hallräumen (ISO 354:2003)
Acoustique - Mesurage de l'absorption acoustique en salle réverbérante (ISO 354:2003)
Ta slovenski standard je istoveten z: EN ISO 354:2003
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 354
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2003
ICS 91.120.20 Supersedes EN ISO 354:1993
English version
Acoustics - Measurement of sound absorption in a reverberation
room (ISO 354:2003)
Acoustique - Mesurage de l'absorption acoustique en salle Akustik - Messung der Schallabsorption in Hallräumen
réverbérante (ISO 354:2003) (ISO 354:2003)
This European Standard was approved by CEN on 23 April 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 354:2003 E
worldwide for CEN national Members.

CORRECTED  2003-09-24
Foreword
This document (EN ISO 354:2003) has been prepared by Technical Committee ISO/TC 43
"Acoustics" in collaboration with Technical Committee CEN/TC 126 "Acoustic properties of
building products and of buildings", the secretariat of which is held by AFNOR.
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 November 2003, and conflicting national
standards shall be withdrawn at the latest by November 2003.
This document supersedes EN ISO 354:1993.
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 354:2003 has been approved by CEN as EN ISO 354:2003 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 266 1997 Acoustics - Preferred frequencies EN ISO 266 1997
INTERNATIONAL ISO
STANDARD 354
Second edition
2003-05-15
Acoustics — Measurement of sound
absorption in a reverberation room
Acoustique — Mesurage de l'absorption acoustique en salle
réverbérante
Reference number
ISO 354:2003(E)
©
ISO 2003
ISO 354:2003(E)
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ii © ISO 2003 — All rights reserved

ISO 354:2003(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 1
4 Principle . 3
5 Frequency range . 3
6 Test arrangement. 3
6.1 Reverberation room and diffusion of sound field . 3
6.2 Test specimens . 4
6.3 Temperature and relative humidity . 5
7 Measurement of reverberation time. 5
7.1 General. 5
7.2 Interrupted noise method. 6
7.3 Integrated impulse response method. 7
7.4 Evaluation of reverberation times based on decay curves . 9
8 Expression of results. 9
8.1 Method of calculation . 9
8.2 Precision . 11
8.3 Presentation of results . 12
9 Test report . 13
Annex A (normative) Diffusivity of the sound field in the reverberation room. 14
Annex B (normative) Test specimen mountings for sound absorption tests. 15
Bibliography . 21

ISO 354:2003(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 354 was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 2, Building
acoustics.
This second edition cancels and replaces the first edition (ISO 354:1985), which has been technically revised,
as follows:
 an integrated impulse response method has been introduced;
 the requirement to measure at least 36 decays has been added;
 mounting conditions according to ISO 354:1985:Amd.1:1997 and mounting conditions Type B and Type J
have been introduced.
iv © ISO 2003 — All rights reserved

ISO 354:2003(E)
Introduction
When a sound source operates in an enclosed space, the level to which reverberant sound builds up, and the
subsequent decay of reverberant sound when the source is stopped, are governed by the sound-absorbing
characteristics of the boundary surfaces, the air filling the space, and objects within the space. In general, the
fraction of the incident sound power absorbed at a surface depends upon the angle of incidence. In order to
relate the reverberation time of an auditorium, office, workshop, etc., to the noise reduction that would be
effected by an absorbing treatment, knowledge of the sound-absorbing characteristics of the surfaces, usually
in the form of a suitable average over all angles of incidence, is required. Since the distribution of sound
waves in typical enclosures includes a wide and largely unpredictable range of angles, a uniform distribution is
taken as the basic condition for the purposes of standardization. If, in addition, the sound intensity is
independent of the location within the space, the sound distribution is called a diffuse sound field, and the
sounds reaching a room surface are said to be at random incidence.
The sound field in a properly designed reverberation room closely approximates a diffuse field. Hence, sound
absorption measured in a reverberation room closely approximates the sound absorption that would be
measured under the basic conditions assumed for standardization.
The purpose of this International Standard is to promote uniformity in the methods and conditions of
measurement of sound absorption in reverberation rooms.
INTERNATIONAL STANDARD ISO 354:2003(E)

Acoustics — Measurement of sound absorption
in a reverberation room
1 Scope
This International Standard specifies a method of measuring the sound absorption coefficient of acoustical
materials used as wall or ceiling treatments, or the equivalent sound absorption area of objects, such as
furniture, persons or space absorbers, in a reverberation room. It is not intended to be used for measuring the
absorption characteristics of weakly damped resonators.
The results obtained can be used for comparison purposes and for design calculation with respect to room
acoustics and noise control.
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 266, Acoustics ― Preferred frequencies
ISO 9613-1, Acoustics ― Attenuation of sound during propagation outdoors ― Part 1: Calculation of the
absorption of sound by the atmosphere
IEC 61260, Electroacoustics ― Octave-band and fractional-octave-band filters
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
3.1
decay curve
graphical representation of the decay of the sound pressure level in a room as a function of time after the
sound source has stopped
3.2
reverberation time
T
time, in seconds, that would be required for the sound pressure level to decrease by 60 dB after the sound
source has stopped
NOTE 1 The definition of T with a decrease by 60 dB of the sound pressure level can be fulfilled by linear extrapolation
of shorter evaluation ranges.
NOTE 2 This definition is based on the assumptions that, in the ideal case, there is a linear relationship between the
sound pressure level and time, and that the background noise level is sufficiently low.
ISO 354:2003(E)
3.3
interrupted noise method
method of obtaining decay curves by direct recording of the decay of the sound pressure level after exciting a
room with broadband or band-limited noise
3.4
integrated impulse response method
method of obtaining decay curves by reverse-time integration of the squared impulse responses
3.5
impulse response
temporal evolution of the sound pressure observed at a point in a room as a result of the emission of a Dirac
impulse at another point in the room
NOTE It is impossible in practice to create and radiate true Dirac delta functions, but short transient sounds (e.g. from
shots) may offer close enough approximations for practical measurements. An alternative measurement technique,
however, is to use a period of maximum-length sequence type signal (MLS) or another deterministic, flat-spectrum signal
and to transform the measured response back to an impulse response.
3.6
equivalent sound absorption area of a room
hypothetical area of a totally absorbing surface without diffraction effects which, if it were the only absorbing
element in the room, would give the same reverberation time as the room under consideration
NOTE 1 The area is measured in square metres.
NOTE 2 For the empty reverberation room, this quantity is denoted by A ; for the reverberation room containing the
test specimen, it is denoted by A .
3.7
equivalent sound absorption area of the test specimen
A
T
difference between the equivalent sound absorption area of the reverberation room with and without the test
specimen
NOTE The area is measured in square metres.
3.8
area of the test specimen
S
area of the floor or wall covered by the test specimen
NOTE 1 The area is measured in square metres.
NOTE 2 In the case of a test specimen surrounded by a structure (type E mounting or type J mounting), it is the area
enclosed by the structure.
3.9
sound absorption coefficient
α
s
ratio of the equivalent sound absorption area of a test specimen divided by the area of the test specimen
NOTE 1 For absorbers where both sides are exposed, the sound absorption coefficient is the equivalent sound
absorption area of the test specimen divided by the area of the two sides of the test specimen.
NOTE 2 The sound absorption coefficient evaluated from reverberation time measurements can have values larger
than 1,0 (e.g. because of diffraction effects), and α is not, therefore, expressed as a percentage.
s
NOTE 3 The use of the subscript “s” is to avoid confusion with the sound absorption coefficient defined as the ratio of
non-reflected-to-incident sound energy if a plane wave strikes a plane wall at a particular angle of incidence. That
“geometric” sound absorption coefficient is always smaller than 1,0 and may therefore be expressed as a percentage.
2 © ISO 2003 — All rights reserved

ISO 354:2003(E)
4 Principle
The average reverberation time in the reverberation room is measured with and without the test specimen
mounted. From these reverberation times, the equivalent sound absorption area of the test specimen, A , is
T
calculated by using Sabine’s equation (see 8.1.2.1).
In the case of a test specimen that uniformly covers a surface (a plane absorber or a specified array of test
objects), the sound absorption coefficient is obtained by dividing A by the treated surface area S (see 3.8).
T
When the test specimen comprises several identical objects, the equivalent sound absorption area A of an
obj
individual object is found by dividing A by the number of objects, n:
T
A = A /n
obj T
5 Frequency range
Measurements shall be made in one-third-octave bands with the following centre frequencies, in hertz, as
specified in ISO 266:
100 125 160 200 250 315
400 500 630 800 1 000 1 250
1 600 2 000 2 500 3 150 4 000 5 000
Additional measurements may be made in one-third-octave bands with centre frequencies specified by
ISO 266 outside this range. Especially at low frequencies (below 100 Hz), it could be very difficult to obtain
accurate measurement results due to the low modal density of the reverberation room.
6 Test arrangement
6.1 Reverberation room and diffusion of sound field
6.1.1 Volume of reverberation room
The volume of the reverberation room shall be at least 150 m . For new constructions, the volume is strongly
3 3
recommended to be at least 200 m . When the volume of the room is greater than about 500 m , it may not
be possible to measure sound absorption accurately at high frequencies because of air absorption.
6.1.2 Shape of reverberation room
The shape of the reverberation room shall be such that the following condition is fulfilled:
1/ 3
IV< 1, 9 (1)
max
where
I is the length of the longest straight line which fits within the boundary of the room (e.g. in a
max
rectangular room it is the major diagonal), in metres;
V is the volume of the room, in cubic metres.
In order to achieve a uniform distribution of natural frequencies, especially in the low-frequency bands, no two
dimensions of the room shall be in the ratio of small whole numbers.
ISO 354:2003(E)
6.1.3 Diffusion of the sound field
The decaying sound field in the room shall be sufficiently diffuse. In order to achieve satisfactory diffusion
whatever the shape of the room, the use of stationary or suspended diffusers or rotating vanes is, in general,
required (see Annex A).
6.1.4 Sound absorption area
The equivalent sound absorption area of the empty room, A , calculated according to 8.1.2.1, determined in
one-third octave bands, shall not exceed the values given in Table 1.
Table 1 — Maximum equivalent sound absorption areas for room volume V = 200 m
Frequency, Hz 100 125 160 200 250 315 400 500 630
6,5 6,5 6,5 6,5 6,5 6,5 6,5 6,5 6,5
Equivalent sound absorption area, m

Frequency, Hz 800 1 000 1 250 1 600 2 000 2 500 3 150 4 000 5 000
6,5 7,0 7,5 8,0 9,5 10,5 12,0 13,0 14,0
Equivalent sound absorption area, m

If the volume V of the room differs from 200 m , the values given in Table 1 shall be multiplied by
3 2/3
(V/200 m ) .
The graph of the equivalent sound absorption area of the empty room versus the frequency shall be a smooth
curve and shall have no dips or peaks differing by more than 15 % from the mean of the values of both
adjacent one-third-octave bands.
6.2 Test specimens
6.2.1 Plane absorbers
2 2
6.2.1.1 The test specimen shall have an area between 10 m and 12 m . If the volume V of the room is
3 3 2/3
greater than 200 m , the upper limit for the test specimen area shall be increased by the factor (V/200 m ) .
The area to be chosen depends on the room volume and on the absorption capability of the test specimen.
The larger the room, the larger the test area should be. For specimens with small absorption coefficient, the
upper limit area should be chosen.
6.2.1.2 The test specimen shall be of rectangular shape with a ratio of width to length of between 0,7
and 1. It should be placed so that no part of it is closer than 1 m to any edge of the boundary of the room; the
distance shall be at least 0,75 m. The edges of the specimen shall preferably not be parallel to the nearest
edge of the room. If necessary, heavy test specimens may be mounted vertically along the walls of the room,
and directly resting on the floor. In this case, the requirement of at least 0,75 m distance need not be
respected.
6.2.1.3 The test specimen shall be installed in one of the mountings specified in Annex B, unless the
relevant specifications provided by the producer or the application details provided by the user require a
different mounting. The measurement of the reverberation time of the empty room shall be made in the
absence of the frame or the side walls of the test specimen except for the barrier around a Type J mounting.
6.2.2 Discrete sound absorbers
6.2.2.1 Rectangular unit sound absorber pads or baffles shall be installed in a Type J mounting as
specified in Annex B.
4 © ISO 2003 — All rights reserved

ISO 354:2003(E)
6.2.2.2 Discrete objects (e.g. chairs, free-standing screens or persons) shall be installed for the test in the
same manner as they are typically installed in practice. For example, chairs or free-standing screens shall rest
on the floor, but they shall not be closer than 1 m to any other boundary. Space absorbers shall be mounted at
least 1 m from any boundary or room diffusers and at least 1 m from any microphone. Office screens shall be
mounted as individual objects.
6.2.2.3 A test specimen shall comprise a sufficient number of individual objects (in general, at least three)
to provide a measurable change in the equivalent sound absorption area of the room greater than 1 m , but
2 3
not more than 12 m . If the volume, V, of the room is greater than 200 m , these values shall be increased by
3 2/3
the factor (V/200 m ) . Objects normally treated as individual objects shall be arranged randomly, spaced at
least 2 m apart. If the test specimen comprises only one object, it shall be tested in at least three locations, at
least 2 m apart, and the results shall be averaged.
6.3 Temperature and relative humidity
6.3.1 Changes in temperature and relative humidity during the course of a measurement can have a
large effect on the measured reverberation time, especially at high frequencies and at low relative humidities.
The changes are described quantitatively in ISO 9613-1.
6.3.2 Measurements should be performed in the empty room and in the room containing the test
specimen under conditions of temperature and relative humidity that are almost the same so that the
adjustments due to air absorption do not differ significantly. In any case, the relative humidity in the room shall
be at least 30 % and max. 90 % and the temperature shall be at least 15 °C during the whole test. For all
measurements, the corrections for the change in air absorption as described in 8.1.2.3 shall be applied.
Allow the test specimen to reach equilibrium with respect to temperature and relative humidity in the room
before tests are carried out.
7 Measurement of reverberation time
7.1 General
7.1.1 Introduction
Two methods of measuring decay curves are described in this International Standard: the interrupted noise
method and the integrated impulse response method. The decay curve measured with the interrupted noise
method is the result of a statistical process, and averaging several decay curves or reverberation times
measured at one microphone/loudspeaker position is mandatory in order to obtain a suitable repeatability. The
integrated impulse response of a room is a deterministic function and not prone to statistical deviations, so no
averaging is necessary. However, it requires more sophisticated instrumentation and data processing than the
interrupted noise method.
7.1.2 Microphones and microphone positions
The directivity characteristic of the microphones used for the measurement shall be omnidirectional. The
measurements shall be made with different microphone positions which are at least 1,5 m apart, 2 m from any
sound source and 1 m from any room surface and the test specimen. Decay curves measured at different
microphone positions shall not be combined in any way.
7.1.3 Source positions
The sound in the reverberation room shall be generated by a sound source with an omnidirectional radiation
pattern. Different sound source positions which are at least 3 m apart shall be used.
ISO 354:2003(E)
7.1.4 Number of microphone and loudspeaker positions
The number of spatially independent measured decay curves shall be at least 12. Therefore the number of
microphone positions times the number of sound source positions shall be at least 12. The minimum number
of microphone positions shall be three, the minimum number of sound source positions shall be two. It is
permissible to use more than one sound source simultaneously provided the difference in the radiated power
is within a tolerance band of 3 dB for each one-third-octave band. If more than one sound source is used for
excitation simultaneously, the number of spatially independent measured decay curves may be reduced to six.
7.2 Interrupted noise method
7.2.1 Excitation of the room
A loudspeaker source shall be used and the signal fed into the loudspeaker shall be derived from broad-band
or band-limited noise having a continuous frequency spectrum. When using broad-band noise and a real-time
analyser, the spectrum of the noise used shall be such that the differences in the resulting sound pressure
levels in the room shall be less than 6 dB in adjacent one-third-octave bands. When using band-limited noise,
the bandwidth shall be at least one-third octave.
The excitation signal shall be sufficiently long to produce a steady-state sound pressure level in all frequency
bands of interest before it is switched off. In order to obtain steady-state conditions, the excitation time shall
be at least half of the estimate of the expected reverberation time.
The level of the excitation signal before decay shall be sufficiently high that the lower decibel level of the
evaluation range is at least 10 dB above the background noise level (see 7.4.1).
If a signal with a bandwidth greater than one-third octave is used, reverberation times of different length in
adjacent frequency bands can influence the lower part of the decay curve. If the reverberation times in
adjacent bands differ by more than a factor of 1,5, the decay curves for those bands with the shortest
reverberation times shall be measured individually using one-third-octave band filtering of the sound source.
7.2.2 Averaging
As explained in 7.1.1, averaging several measurements performed at one microphone/loudspeaker position is
mandatory in order to reduce the measurement uncertainty caused by statistical deviations. The number of
averages shall be at least three. If the desired repeatability is to be in the same range as the repeatability
produced by the integrated impulse response method, the number of averages shall be at least ten (see 8.2).
Two averaging methods are possible. The first averaging method is to average the decay curves recorded at
one microphone/loudspeaker position using the formula
L ()t

pn
N

Lt() =10 lg 10 (2)
p
∑

N
n=1


where
L (t) is the averaged sound pressure level at the time t calculated for a total number of N decays;
p
L (t) is the sound pressure level of the nth decay at the time t.
pn
This method is generally referred to as “ensemble averaging”. As the second averaging method to be applied
in cases where ensemble averaging is not possible, the single decay curves
...