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
Current Stage
9092 - Decision on results of review/2YR ENQ - revise - Review Enquiry
Due Date
11-Jun-2008
Completion Date
11-Jun-2008

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SLOVENSKI STANDARD
SIST EN ISO 354:2004
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
SIST EN ISO 354:2004 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
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.
---------------------- Page: 2 ----------------------
EN ISO 354:2003 (E)
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).

---------------------- Page: 3 ----------------------
EN ISO 354:2003 (E)
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
---------------------- Page: 4 ----------------------
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
---------------------- Page: 5 ----------------------
ISO 354:2003(E)
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ii © ISO 2003 — All rights reserved
---------------------- Page: 6 ----------------------
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 2003 — All rights reserved iii
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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
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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.
© ISO 2003 — All rights reserved v
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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

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 2003 — All rights reserved 1
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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

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
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

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.

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
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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

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).

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:
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 2003 — All rights reserved 3
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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
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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 2003 — All rights reserved 5
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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.

...

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