EN ISO 3382-1:2009

SLOVENSKI STANDARD
01-september-2009
1DGRPHãþD
SIST EN ISO 3382:2001
$NXVWLND0HUMHQMHDNXVWLþQLKSDUDPHWURYYSURVWRULKGHO3URVWRUL]D
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Acoustics - Measurement of room acoustic parameters - Part 1: Performance spaces
(ISO 3382-1:2009)
Acoustique - Mesurage des parametres acoustiques des salles - Partie 1: Salles de
spectacles (ISO 3382-1:2009)
Ta slovenski standard je istoveten z: EN ISO 3382-1:2009
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 3382-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2009
ICS 91.120.20 Supersedes EN ISO 3382:2000
English Version
Acoustics - Measurement of room acoustic parameters - Part 1:
Performance spaces (ISO 3382-1:2009)
Acoustique - Mesurage des paramètres acoustiques des Akustik - Messung von raumakustischen Parametern - Teil
salles - Partie 1: Salles de spectacles (ISO 3382-1:2009) 1: Aufführungsplätze (ISO 3382-1:2009)
This European Standard was approved by CEN on 14 June 2009.
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, 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
© 2009 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 3382-1:2009: E
worldwide for CEN national Members.

Contents Page
Foreword .3

Foreword
This document (EN ISO 3382-1:2009) has been prepared by Technical Committee ISO/TC 43 "Acoustics" in
collaboration with Technical Committee CEN/TC 126 “Acoustic properties of building elements 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 December 2009, and conflicting national standards shall be withdrawn
at the latest by December 2009.
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 3382:2000.
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, 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 3382-1:2009 has been approved by CEN as a EN ISO 3382-1:2009 without any modification.

INTERNATIONAL ISO
STANDARD 3382-1
First edition
2009-06-15
Acoustics — Measurement of room
acoustic parameters —
Part 1:
Performance spaces
Acoustique — Mesurage des paramètres acoustiques des salles —
Partie 1: Salles de spectacles

Reference number
ISO 3382-1:2009(E)
©
ISO 2009
ISO 3382-1:2009(E)
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ii © ISO 2009 – All rights reserved

ISO 3382-1:2009(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Measurement conditions .3
5 Measurement procedures .6
6 Evaluation of decay curves .8
7 Measurement uncertainty .9
8 Spatial averaging .10
9 Statement of results.10
Annex A (informative) Auditorium measures derived from impulse responses .12
Annex B (informative) Binaural auditorium measures derived from impulse responses .21
Annex C (informative) Stage measures derived from impulse responses.23
Bibliography .25

ISO 3382-1:2009(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 3382-1 was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 2, Building
acoustics.
This first edition of ISO 3382-1, together with ISO 3382-2 and ISO 3382-3, cancels and replaces
ISO 3382:1997, of which it constitutes a technical revision. Annex A has been extended with information on
JND (just noticeable difference), recommended frequency averaging and by the addition of a new parameter
for LEV (listener envelopment). A new Annex C has been added with parameters for the acoustic conditions
on the orchestra platform.
ISO 3382 consists of the following parts, under the general title Acoustics — Measurement of room acoustic
parameters:
⎯ Part 1: Performance spaces
⎯ Part 2: Reverberation time in ordinary rooms
Open plan spaces are to form the subject of a future part 3.
iv © ISO 2009 – All rights reserved

ISO 3382-1:2009(E)
Introduction
The reverberation time of a room was once regarded as the predominant indicator of its acoustical properties.
While reverberation time continues to be regarded as a significant parameter, there is reasonable agreement
that other types of measurements, such as relative sound pressure levels, early/late energy ratios, lateral
energy fractions, interaural cross-correlation functions and background noise levels, are needed for a more
complete evaluation of the acoustical quality of rooms.
This part of ISO 3382 establishes a method for obtaining reverberation times from impulse responses and
from interrupted noise. The annexes introduce the concepts and details of measurement procedures for some
of the newer measures, but these do not constitute a part of the formal specifications of this part of ISO 3382.
The intention is to make it possible to compare reverberation time measurements with higher certainty and to
promote the use of and consensus in measurement of the newer measures.
Annex A presents measures based on squared impulse responses: a further measure of reverberation (early
decay time) and measures of relative sound levels, early/late energy fractions and lateral energy fractions in
auditoria. Within these categories, there is still work to be done in determining which measures are the most
suitable to standardize upon; however, since they are all derivable from impulse responses, it is appropriate to
introduce the impulse response as the basis for standard measurements. Annex B introduces binaural
measurements and the head and torso simulators (dummy heads) required to make binaural measurements
in auditoria. Annex C introduces the support measures that have been found useful for evaluating the acoustic
conditions from the musicians’ point of view.
INTERNATIONAL STANDARD ISO 3382-1:2009(E)

Acoustics — Measurement of room acoustic parameters —
Part 1:
Performance spaces
1 Scope
This part of ISO 3382 specifies methods for the measurement of reverberation time and other room acoustical
parameters in performance spaces. It describes the measurement procedure, the apparatus needed, the
coverage required, and the method of evaluating the data and presenting the test report. It is intended for the
application of modern digital measuring techniques and for the evaluation of room acoustical parameters
derived from impulse responses.
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.
IEC 61260, Electroacoustics — Octave-band and fractional-octave-band filters
IEC 61672-1, Electroacoustics — Sound level meters — Part 1: Specifications
3 Terms and definitions
For the purposes of this part of ISO 3382, 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
[ISO 354:2003, 3.1]
NOTE 1 It is possible to measure this decay either after the actual cut-off of a continuous sound source in the room or
derived from the reverse-time integrated squared impulse response of the room (see Clause 5).
NOTE 2 The decay directly obtained after non-continuous excitation of a room (e.g. by recording a gunshot with a level
recorder) is not recommended for accurate evaluation of the reverberation time. This method ought only be used for
survey purposes. The decay of the impulse response in a room is in general not a simple exponential decay, and thus the
slope is different from that of the integrated impulse response.
3.2
interrupted noise method
method of obtaining decay curves by direct recording of the decay of sound pressure level after exciting a
room with broadband or band limited noise
[ISO 354:2003, 3.3]
ISO 3382-1:2009(E)
3.3
integrated impulse response method
method of obtaining decay curves by reverse-time integration of the squared impulse responses
[ISO 354:2003, 3.4]
3.4
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
[ISO 354:2003, 3.5]
NOTE It is impossible in practice to create and radiate true Dirac delta functions, but short transient sounds (e.g. from
gunshots) can offer close enough approximations for practical measurement. An alternative measurement technique,
however, is to use a period of maximum-length sequence (MLS) type signal or other deterministic, flat-spectrum signal like
a sine sweep and transform the measured response back to an impulse response.
3.5
reverberation time
T
〈room acoustic parameters〉 duration required for the space-averaged sound energy density in an enclosure to
decrease by 60 dB after the source emission has stopped
NOTE 1 The reverberation time is expressed in seconds.
NOTE 2 T can be evaluated based on a smaller dynamic range than 60 dB and extrapolated to a decay time of 60 dB.
It is then labelled accordingly. Thus, if T is derived from the time at which the decay curve first reaches 5 dB and 25 dB
below the initial level, it is labelled T . If decay values of 5 dB to 35 dB below the initial level are used, it is labelled T .
20 30
3.6 States of occupancy
3.6.1
unoccupied state
state of a room prepared for use and ready for speakers or for performers and audience, but without these
persons being present, and in the case of concert halls and opera houses, preferably with the performers'
chairs, music stands and percussion instruments, etc.
3.6.2
studio state
〈rooms for speech and music〉 state of a room occupied by performers or speakers only and without an
audience (for example, during rehearsals or sound recordings) and with the number of performers and other
persons such as technicians corresponding to the usual number
3.6.3
occupied state
state of an auditorium or theatre when 80 % to 100 % of the seats are occupied
NOTE Reverberation time measured in a room will be influenced by the number of people present and the above
states of occupancy are defined for measurement purposes.
2 © ISO 2009 – All rights reserved

ISO 3382-1:2009(E)
4 Measurement conditions
4.1 General
The measurements of reverberation time may be made with the room in any or all states of occupancy. Where
the room has adjustable components for providing variable acoustical conditions, it can be relevant to carry
out separate measurements with these components in each of their normal settings. The temperature and
relative humidity of the air in the room should be measured to an accuracy of ± 1 °C and ± 5 %, respectively.
An accurate description of the state of occupancy of the room is of decisive importance in assessing the
results obtained by measuring the reverberation time. Extraordinary occupancies (such as that which would
be created in a concert hall by a larger than usual orchestra or the additional presence of a choir or standees)
shall be noted with the results.
In theatres, a distinction shall be made between “safety curtain up” and “safety curtain down”, between
“orchestra pit open” and “orchestra pit closed”, and also between “orchestra seated on the stage”, with and
without concert enclosure. In all of these cases, measurement can be useful. If the safety curtain is up, the
amount of furnishing of the stage is of importance and shall be described.
Where variable components involve active (i.e. electronic) techniques, the effects of these should be
measured, too, but as certain types of electronic reverberation enhancement systems create non-time-
stationary conditions in the room, a unique impulse response will not exist and caution should be exercised in
using synchronous averaging during the course of making measurements.
4.2 Equipment
4.2.1 Sound source
The sound source shall be as close to omnidirectional as possible (see Table 1). It shall produce a sound
pressure level sufficient to provide decay curves with the required minimum dynamic range, without
contamination by background noise. In the case of measurements of impulse responses using
pseudo-random sequences, the required sound pressure level might be quite low because a strong
improvement of the signal-to-noise ratio by means of synchronous averaging is possible. In the case of
measurements which do not use a synchronous averaging (or other) technique to augment the decay range, a
source level will be required that gives at least 45 dB above the background level in the corresponding
frequency band. If only T is to be measured, it is sufficient to create a level at least 35 dB above the
background level.
Table 1 lists the maximum acceptable deviations from omnidirectionality when averaged over “gliding”
30° arcs in a free sound field. In case a turntable cannot be used, measurements per 5° should be performed,
followed by “gliding” averages, each covering six neighbouring points. The reference value shall be
determined from a 360° energetic average in the measurement plane. The minimum distance between source
and microphone shall be 1,5 m during these measurements.
Table 1 — Maximum deviation of directivity of source in decibels for excitation
with octave bands of pink noise and measured in free field
Frequency, hertz
125 250 500 1 000 2 000 4 000
Maximum deviation, decibels
± 1 ± 1 ± 1 ± 3 ± 5 ± 6
ISO 3382-1:2009(E)
4.2.2 Microphones, recording and analysis equipment
4.2.2.1 General
Omnidirectional microphones shall be used to detect the sound pressure and the output may be taken either
⎯ directly to an amplifier, filter set and a system for displaying decay curves or analysis equipment for
deriving the impulse responses, or
⎯ to a signal recorder for later analysis.
4.2.2.2 Microphone and filters
The measurement equipment shall meet the requirements of a type 1 sound level meter according to
IEC 61672-1. The octave or one-third-octave filters shall conform with IEC 61260. The microphone should be
as small as possible and preferably have a maximum diaphragm diameter of 13 mm. Microphones with
diameters up to 26 mm are allowed, if they are of the pressure response type or of the free field response type
but supplied with a random incidence corrector yielding a flat frequency response at random incidence.
4.2.2.3 Recording device
If the sound decay is initially recorded on magnetic tape or a digital recording device, automatic gain control or
other circuits for dynamic optimization of signal-to-noise ratio shall not be used. The recording time of each
decay shall be sufficiently long to enable determination of the final background level following the decay; five
seconds plus the expected reverberation time is recommended as a minimum.
The recording device shall have the following characteristics for the particular combination of record and
playback speeds used.
a) The frequency response shall be flat over the frequency range of measurement with a smaller tolerance
than ± 3 dB.
b) The dynamic range shall be sufficient to allow the required minimum decay curve range. In the case of
interrupted noise decays, the recorder shall be capable of providing a signal-to-noise ratio of at least
50 dB in every frequency band concerned.
0,1 × n
c) The ratio of the playback speed to the record speed shall be within ± 2 % of 10 , where n is an
integer including zero.
NOTE If speed translation is used on playback, the corresponding frequency translation will then be a whole number
of standard one-third-octave band spacings or, if n is a multiple of three, of octave band spacings.
Where a tape recorder is used, then in respect of the speed of response of the apparatus for forming a record
of the decay of sound pressure level with time (see 4.2.2.4), T refers to the effective reverberation time of the
signal being played back. This will differ from the true reverberation time of the enclosure only if the playback
speed differs from the record speed.
When the decay has been recorded for replay through filters and an integrating device, it can be beneficial to
time-reverse the responses during replay (see Reference [10]).
4.2.2.4 Apparatus for forming decay record of level
The apparatus for forming (and displaying and/or evaluating) the decay record shall use any of the following:
a) exponential averaging, with continuous curve as output;
b) exponential averaging, with successive discrete sample points from the continuous average as output;
c) linear averaging, with successive discrete linear averages as output (in some cases, with small pauses
between performance of averages).
4 © ISO 2009 – All rights reserved

ISO 3382-1:2009(E)
The averaging time, i.e. time constant of an exponential averaging device (or appropriate equivalent), shall be
less than, but as close as possible to, T/30. Similarly, the averaging time of a linear averaging device shall be
less than T/12. Here T is the reverberation time being measured or, if appropriate, the effective reverberation
time as described in the penultimate paragraph of 4.2.2.3.
In apparatus where the decay record is formed as a succession of discrete points, the time interval between
points on the record shall be less than 1,5 times the averaging time of the device.
In all cases where the decay record is to be evaluated visually, adjust the time scale of the display so that the
slope of the record is as close as possible to 45°.
NOTE 1 The averaging time of an exponential averaging device is equal to 4,34 dB [= 10 lg(e)] divided by the decay
rate in decibels per second of the device.
NOTE 2 Commercial level recorders, in which sound pressure level is recorded graphically as a function of time, are
approximately equivalent to exponential averaging devices.
NOTE 3 When an exponential averaging device is used, there is little advantage in setting the averaging time very
much less than T/30. When a linear averaging device is used, there is no advantage in setting the interval between points
at very much less than T/12. In some sequential measuring procedures, it is feasible to reset the averaging time
appropriately for each frequency band. In other procedures, this is not feasible, and an averaging time or interval chosen
as above with reference to the shortest reverberation time in any band has to serve for measurements in all bands.
4.2.2.5 Overload
No overloading shall be allowed in any stage of the measuring apparatus. Where impulsive sound sources are
used, peak-level indicating devices shall be used for checking against overloading.
4.3 Measurement positions
Source positions should be located where the natural sound sources in the room would typically be located. A
minimum of two source positions shall be used. The height of the acoustic centre of the source should be
1,5 m above the floor.
Microphone positions should be at positions representative of positions where listeners would normally be
located. For reverberation time measurements, it is important that the measurement positions sample the
entire space; for the room acoustic parameters described in Annexes A and B, they should also be selected to
provide information on possible systematic variations with position in the room. Microphone positions shall be
at least half a wavelength apart, i.e. a distance of around 2 m for the usual frequency range. The distance
from any microphone position to the nearest reflecting surface, including the floor, shall be at least a quarter of
a wavelength, i.e. normally around 1 m. See A.4 for more details.
No microphone position shall be too close to any source position, in order to avoid a too-strong influence from
the direct sound. In rooms for speech and music, the height of the microphones above the floor should be
1,2 m, corresponding to the ear height of average listeners in typical chairs.
A distribution of microphone positions shall be chosen that anticipates the major influences likely to cause
differences in reverberation time throughout the room. Obvious examples are the differences for seating areas
close to walls, underneath balconies or in spaces which are decoupled (e.g. in church transepts and chancels
compared with church naves). This requires a judgement of the evenness of the “acoustical” distribution to the
different seating areas, the equality of the coupling of the separate parts of the volume and the proximity to
local perturbations.
For reverberation time measurement, it can be useful to assess the room against the following criteria (which
in many cases will simply require a visual assessment) to determine whether single spatial averages will
adequately describe the room:
ISO 3382-1:2009(E)
a) the materials of the boundary surfaces and any suspended elements are such that, judged in terms of
their absorption and diffusion properties, they are reasonably evenly distributed among the surfaces
which surround the room, and
b) all parts of the room volume communicate reasonably equally with each other, in which case three or four
microphone positions will be adequate — these positions being chosen to cover the seating area, in an
evenly spaced array — and the results of the measurements may be averaged.
For a) above, if the ceiling, side, front and rear walls, when assessed individually, have no regions covering
more than 50 % of their respective areas, with properties different from those of the remaining surfaces, then it
may be considered that the distribution is acceptably even (in some spaces it can be helpful to approximate
the room geometry to a rectangular parallelepiped for this assessment).
For b) above, the room volume may be considered to operate as a single space if there are no parts of the
floor area which have their lines-of-sight blocked to any other part of the room that is more than 10 % of the
total room volume.
If these conditions are not satisfied, then the room is likely to show areas with differing reverberation times,
and these shall be investigated and measured separately.
5 Measurement procedures
5.1 General
Two methods of measuring the reverberation time are described in this part of ISO 3382: the interrupted noise
method and the integrated impulse response method. Both methods have the same expectation value. The
frequency range depends on the purpose of the measurements. Where there is no requirement for specific
frequency bands, the frequency range should cover at least 250 Hz to 2 000 Hz for the survey method. For
the engineering and precision methods, the frequency range should cover at least 125 Hz to 4 000 Hz in
octave bands, or 100 Hz to 5 000 Hz in one-third octave bands.
5.2 Interrupted noise method
5.2.1 Excitation of the room
A loudspeaker source shall be used and the signal fed into the loudspeaker shall be derived from broadband
random or pseudo-random electrical noise. When using a pseudo-random noise, it shall be randomly ceased,
not using a repeated sequence. The source shall be able to produce a sound pressure level sufficient to
ensure a decay curve starting at least 35 dB above the background noise in the corresponding frequency
band. If T is to be measured, it is necessary to create a level at least 45 dB above the background level in
each frequency band.
For measurements in octave bands, the bandwidth of the signal shall be greater than one octave, and for
measurements in one-third-octave bands, the bandwidth of the signal shall be greater than one-third octave.
The spectrum shall be reasonably flat within the actual octave band to be measured. Alternatively, the
broadband noise spectrum may be shaped to provide a pink spectrum of steady-state reverberant sound in
the enclosure from 88 Hz to 5 657 Hz. Thus, the frequency range covers the one-third-octave bands with
mid-band frequencies from 100 Hz to 5 kHz or octave bands from 125 Hz to 4 kHz.
For the engineering and precision methods, the duration of excitation of the room needs to be sufficient for the
sound field to have achieved a steady state before the source is switched off. Thus, it is essential for the noise
to be radiated for at least a few seconds and not less than half the reverberation time.
For the survey method, a short excitation or an impulse signal may be used as an alternative to the interrupted
noise signal. However, in that case, the measuring accuracy is less than that stated in 7.1.
6 © ISO 2009 – All rights reserved

ISO 3382-1:2009(E)
5.2.2 Averaging of measurements
The number of microphone positions used will be determined by the accuracy required (see Annex A).
However, in view of the randomness inherent in the source signal, it is necessary to average over a number of
measurements at each position in order to achieve an acceptable measurement uncertainty (see 7.1). The
averaging in each position can be made in two different ways: either
⎯ find the individual reverberation times for all the decay curves and take the mean value, or
⎯ make an ensemble average of the squared sound pressure decays and find the reverberation time of the
resulting decay curve.
The individual decays are superposed with their beginnings synchronised. The discrete squared sound
pressure sample values are summed for each time interval increment of the decays and the sequence of
these sums is used as a single overall ensemble decay from which T is then evaluated (see Reference [20]). It
is important that the sound power emitted by the source be kept the same for all measurements. This is the
preferred method.
5.3 Integrated impulse response method
5.3.1 General
The impulse response from a source position to a receiver position in a room is a well-defined quantity that
can be measured in a variety of ways (e.g. using pistol shots, spark gap impulses, noise bursts, chirps or
MLSs as signals). It is not the aim of this part of ISO 3382 to exclude any other method that can yield the
correct impulse response.
5.3.2 Excitation of the room
The impulse response can be measured directly using an impulse source such as a pistol shot or any other
source that is not reverberant itself as long as its spectrum is broad enough to meet the requirements of 5.2.1.
The impulse source shall be able to produce a peak sound pressure level sufficient to ensure a decay curve
starting at least 35 dB above the background noise in the corresponding frequency band. If T is to be
measured, it is necessary to create a level at least 45 dB above the background level.
Special sound signals may be used which yield the impulse response only after special processing of the
recorded microphone signal (see ISO 18233). This can provide an improved signal-to-noise ratio. Sine
sweeps or pseudo-random noise (e.g. MLS) may be used if the requirements for the spectrum and directional
characteristics of the source are fulfilled. Because of the improvement in signal-to-noise ratio, the dynamic
requirements on the source can be considerably lower than those set in the previous paragraph. If time
averaging is used, it is necessary to verify that the averaging process does not alter the measured impulse
response. Using these measuring techniques, the frequency filtering is often inherent in the signal analysis,
and it is sufficient that the excitation signal cover the frequency bands to be measured.
5.3.3 Integration of the impulse response
Generate the decay curve for each octave band by a backward integration of the squared impulse response.
In an ideal situation with no background noise, the integration ought to start at the end of the impulse
response (t →∞) and proceed to the beginning of the squared impulse response. Thus, the decay as a
function of time is, according to Equation (1):
∞ t
E t()==pp()τ ddττ( ) (−τ) (1)
∫∫
t ∞
where
p is the sound pressure of the impulse response as a function of time;
ISO 3382-1:2009(E)
E is the energy of the decay curve as a function of time;
t is the time.
This integral in reverse time is often derived by performing two integrations as in Equation (2):
∞ ∞ t
22 2
(τ)ddττ=− () τ ()τ dτ (2)
pp p
∫ ∫∫
t
In order to minimize the influence of the background noise on the later part of the impulse response, the
following technique may be used.
If the level of the background noise is known, determine the starting point of the integration, t , as the
intersection between a horizontal line through the background noise and a sloping line through a
representative part of the squared impulse response displayed using a decibel scale, and calculate the decay
curve from Equation (3):
t
Et()=−(ττ) d( )+C (3)
p
∫
t
where (t < t ) and C is an optional correction for integrated squared impulse responses between t and infinity.
1 1
The most reliable result is obtained when C is calculated under the assumption of an exponential decay of
energy with the same rate as given by the squared impulse response between t and t , where t is the time
0 1 0
corresponding to a level 10 dB higher than the level at t .
If C is set to zero, the finite starting point of the integration causes a systematic underestimation of the
reverberation time. For a maximum underestimation of 5 %, the level of the background noise must be at least
the evaluation range plus 15 dB below the maximum of the impulse response. For instance, for the
determination of T , the level of the background noise must be at least 45 dB below the maximum.
6 Evaluation of decay curves
For the determination of T , the evaluated range for the decay curves is from 5 dB to 35 dB below the steady
state level. For the integrated impulse response method, the steady state level is the total level of the
integrated impulse response. Within the evaluation range, a least-squares fit line shall be computed for the
curve or, in the case of decay curves plotted directly by level recorder, a straight line shall be fitted manually
as closely as possible to the decay curve. Other algorithms that provide similar results may be used. The
slope of the straight line gives the decay rate, d, in decibels per second, from which the reverberation time is
calculated as T = 60/d. For the determination of T , the evaluation range is from 5 dB to 25 dB.
30 20
If the technique used for determining the reverberation time is based on evaluating traces plotted by a level
recorder, then a visual “best fit” line may be substituted for a computed regression line, but this will not be as
reliable as a regression analysis.
In order to specify a reverberation time, the decay curves shall follow approximately a straight line. If the
curves are wavy or bent, this may indicate a mixture of modes with different reverberation times and thus the
result may be unreliable.
8 © ISO 2009 – All rights reserved

ISO 3382-1:2009(E)
7 Measurement uncertainty
7.1 Interrupted noise method
Due to the random nature of the excitation signal, the measurement uncertainty of the interrupted noise
method strongly depends on the number of averages performed. Ensemble averaging and the averaging of
individual reverberation times have the same dependencies on the number of averages. The standard
deviation of the measurement result σ(T ) or σ(T ), respectively, can be estimated from Equations (4)
20 30
and (5):
11+,90/ n
σ()TT=0,88 (4)
20 20
NBT
11+,52/ n
σ()TT=0,55 (5)
30 30
NBT
where
B is the bandwidth, in hertz;
n is the number of decays measured in each position;
N is the number of independent measurement positions (combinations of source and receiver
positions);
T is the reverberation time, in seconds, based on a 20 dB evaluation range;
T is the reverberation time, in seconds, based on a 30 dB evaluation range.
Equations (4) and (5) are derived from References [21] and [22] and based on certain assumptions
concerning the averaging device.
For an octave filter, B = 0,71 f , and for one-third-octave filter, B = 0,23 f , where f is the mid-band frequency,
c c c
in hertz, of the filter. Octave-band measurements give a better measurement accuracy than one-third-octave
measurements with the same number of measurement positions.
7.2 Integrated impulse response method
Theoretically, the integrated impulse response corresponds to the averaging of an infinite number of
[11]
interrupted noise excitations . For practical evaluation of the measurement uncertainty using the integrated
impulse response method, it can be considered as being of the same order of magnitude as that using an
average of n = 10 measurements in each position with the interrupted noise method. No additional averaging
is necessary to increase the statistical measurement accuracy for each position.
ISO 3382-1:2009(E)
7.3 Lower limits for reliable results caused by filter and detector
In the case of very short reverberation times, the decay curve can be influenced by the filter and the detector.
Using traditional forward analysis, the lower limits for reliable results shall be according to Equations (6)
and (7):
BT> 16 (6)
TT> 2 (7)
det
where
B is the filter bandwidth, in hertz;
T is the measured reverberation time, in seconds;
T is the reverberation time, in seconds, of the averaging detector.
det
8 Spatial averaging
The results measured for the range of source and microphone positions can be combined either for separate
identified areas or for the room as a whole to give spatial average values. This spatial averaging shall be
achieved by arithmetic averaging of the reverberation times. The spatial average is given by taking the mean
of the individual reverberation times for all the independent source and microphone positions. The standard
deviation may be determined to provide a measure of accuracy and the spatial variance of the reverberation
time. See also A.4.
9 Statement of results
9.1 Tables and curves
The evaluated reverberation times for each frequency of measurement shall be both plotted in the form of a
graph and stated in a table.
In the case of a graph, the points shall be connected by straight lines. The abscissa shall present frequency
on a logarithmic scale using a distance of 1,5 cm per octave, while the ordinate shall use either a linear time
scale such that 2,5 cm corresponds to one second or a logarithmic scale with 10 cm corresponding to one
decade. The nominal mid-band frequencies for octave bands according to IEC 61260 should be marked on
the frequency axis.
A single figure reverberation time, T , can be calculated by averaging T in the 500 Hz and 1 000 Hz
30,mid 30
octave bands; T may also be used. Alternatively, take averages over the six one-third-octave bands from
20,mid
400 Hz to 1 250 Hz.
10 © ISO 2009 – All rights reserved

ISO 3382-1:2009(E)
9.2 Test report
The test report shall include the following information:
a) a statement that the measurements were made in conformity with this part of ISO 3382;
b) name and place of the room tested;
c) sketch plan of the room, with an indication of the scale;
d) volume of the room — if the room is not completely enclosed, an explanation should be given of how the
stated volume is defined;
e) for rooms for speech and music, the number and type of seats, e.g. whether upholstered or not, and if the
information is available, the thickness and kind of upholstery, the kind of covering material (porous or
non-porous, seats raised or lowered) and which parts of the seat are covered;
f) a description of the shape and material of the walls and the ceiling;
g) state or states of occupancy during measurements and the number of occupants;
h) condition of any variable equipment such as curtains, public-address system, electronic reverberation
enhancement systems, etc.;
i) for theatres, whether the safety curtain or decorative curtains were up or down;
j) description, where appropriate, of the stage furnishing, including any concert enclosure, etc.;
k) temperature and relative humidity in the room during the measurement;
l) description of measuring apparatus, source and microphones, and whether tape recorders were
employed;
m) description of the sound signal used;
n) coverage chosen, including details of the source and m
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