IEC TR 61305-6:2005

TECHNICAL IEC
REPORT TR 61305-6
First edition
2005-05
Household high-fidelity audio
equipment and systems–
Methods of measuring and specifying
the performance –
Part 6:
Listening tests on loudspeakers –
Single stimulus ratings and
paired comparisons
Reference number
IEC/TR 61305-6:2005(E)
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TECHNICAL IEC
REPORT TR 61305-6
First edition
2005-05
Household high-fidelity audio
equipment and systems–
Methods of measuring and specifying
the performance –
Part 6:
Listening tests on loudspeakers –
Single stimulus ratings and
paired comparisons
 IEC 2005  Copyright - all rights reserved
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mechanical, including photocopying and microfilm, without permission in writing from the publisher.
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– 2 – TR 61305-6  IEC:2005(E)
CONTENTS
FOREWORD.3
INTRODUCTION.5

1 Scope.6
2 Normative references .6
3 Test preparation .6
3.1 Characteristics of the listening room.6
3.2 Loudspeaker position and seat arrangement .7
3.3 Electrical requirements.8
3.4 Level setting.8
3.5 Listening levels for programmes.8
3.6 Programme material .8
3.7 Qualification and number of listeners.8
3.8 Test duration .8
4 Single stimulus ratings .9
4.1 Test procedure .9
4.2 Questionnaire.9
4.3 Test sequence.10
4.4 Reliability of judgements .10
4.5 Variance analysis .11
4.6 Factor analysis .11
4.7 Quality judgement .12
4.8 Representation of the results.12
4.9 Computer programs.13
5 Paired comparisons.14
5.1 Test procedure .14
5.2 Test criteria .14
5.3 Test sequence.15
5.4 Number of contradictory judgements .15
5.5 Determination of the scale values.15
5.6 Variance analysis .15
5.7 Factor analysis .15

Annex A (informative) Example calculation for tests using paired comparison.16

Bibliography.20

TR 61305-6  IEC:2005(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
HOUSEHOLD HIGH-FIDELITY AUDIO EQUIPMENT AND SYSTEMS –
METHODS OF MEASURING AND SPECIFYING THE PERFORMANCE –

Part 6: Listening tests on loudspeakers –
Single stimulus ratings and paired comparisons

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
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agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC 61305-6, which is a technical report, has been prepared by IEC technical committee 100:
Audio, video and multimedia systems and equipment
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
100/855/DTR 100/905/RVC
Full information on the voting for the approval of this technical report can be found in the
report on voting indicated in the above table.

– 4 – TR 61305-6  IEC:2005(E)
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

TR 61305-6  IEC:2005(E) – 5 –
INTRODUCTION
This technical report gives recommendations for establishing, conducting and evaluating
listening tests.
The tests described in this report are to be performed in a room, the size and acoustical
properties are similar to those of an average living room. Specific recommendations about the
room size, acoustical properties, arrangement of loudspeakers and listeners, and
environmental conditions are given.
This technical report describes experimental procedures, including recommendations on the
choice of programme material and the processing and presentation of the final data. It may be
useful to consider some of the recommendations in AES 20. It should be understood that the
topics of experimental design, execution and statistical analysis are complex, and that only
the most general guidelines can be given. It is recommended that professionals with expertise
of experimental design and statistics should be consulted.
The use of multichannel formats, principally for domestic presentation of surround audio and
cinema is becoming more usual. The procedures described in this report are applicable to any
number of channels.
If the number of loudspeakers to be tested is high, the paired comparison listening test is
lengthy because each loudspeaker has to be compared with the other. A shorter method is
the single stimulus rating. With this method, each object is judged once. The rating is almost
independent of the loudspeaker range in test. Each object is rated absolutely, whereas a
paired comparison provides a relative ranking of the order of the loudspeakers in test.
Another technical report for listening test has been published as IEC 60268-13 and it is
expected that the two technical reports should be combined in the maintenance work

– 6 – TR 61305-6  IEC:2005(E)
HOUSEHOLD HIGH-FIDELITY AUDIO EQUIPMENT AND SYSTEMS –
METHODS OF MEASURING AND SPECIFYING THE PERFORMANCE –

Part 6: Listening tests on loudspeakers –
Single stimulus ratings and paired comparisons

1 Scope
This technical report applies to loudspeakers conforming to IEC 61305-5 and intended for
home use.
The purpose of this report is, in addition to objective testing according to IEC 60268-5, to
establish standards for comparison of the sound characteristics of various loudspeakers with
each other.
Two test procedures are described:
– single stimulus ratings;
– paired comparisons.
The procedures described in this report are applicable to any number of channels.
NOTE The test procedures are specified for stereo systems. They can be applied to multichannel systems
accordingly.
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 61305-5, High fidelity audio equipment and systems; Minimum performance requirements
– Part 5: Loudspeakers.
IEC 60268-5, Sound system equipment – Part 5: Loudspeakers.
ISO 3382, Acoustics – Measurement of the reverberation time of rooms with reference to
other acoustical parameters.
3 Test preparation
3.1 Characteristics of the listening room
3 3
The volume of the listening room shall be 80 m ± 20 m with a room height of 2,75 m ±
0,25 m. The room should have a rectangular floor plan, whereby the ratio of the sides to each
other should not exceed 2:1. A square floor plan is not permitted.

TR 61305-6  IEC:2005(E) – 7 –

T  s
1,0
0,8
0,6
0,4
0,2
100 400 1 000 10 000
f  Hz
IEC  635/05
Figure 1 – Range limits for the reverberation time
The reverberation time of the room shall be within the range limits shown in Figure 1. The
reverberation time shall not change by more than +25 % or –20 % within one octave in the
range from 400 Hz to 8 kHz. The reverberation time is to be measured with noise in
1/3 - octave intervals with listeners present as laid down in ISO 3382. Conversion of the
reverberation time measured without listeners to one with listeners is permitted.
Relevant room resonance resulting from furnishings shall be avoided. The distribution of the
absorbing material should be as uniform as possible for all frequencies. In particular, parallel
walls shall not be allowed to reflect sound to a significantly higher degree than the other walls.
This also applies to the floor and the ceiling of the listening room. The AF-rated mean level of
noise in the testing room may not exceed a value of L = 25 dB.
AFm
3.2 Loudspeaker position and seat arrangement
The loudspeaker shall be hidden behind an acoustically transparent screen to avoid
influencing the listener by its design.
The loudspeakers shall be located and listened to in the positions in which they are used
normally (as recommended of the manufacturer). This means, for example, loudspeakers
designed for placement in shelves shall be placed in shelves or in an acoustically equivalent
position. The distances from the floor and the ceiling shall correspond to usual positioning.
Unless otherwise specified, the distance from the walls shall be at least 0,5 m.
The loudspeakers shall be tested in the stereo mode. The angle between the imaginary lines
joining the loudspeakers and the listener should be not less than 45° for each listener. The
loudspeakers shall be positioned so that the stereo base is constant in each case. Only the
two sets of stereo loudspeaker (paired comparison) or the set of stereo loudspeakers to be
tested (single stimulus rating) may be arranged to prevent feedback from other loudspeakers.
When the paired comparison procedure is used, the centre and height of the line between the
loudspeakers of each set shall not vary more than is necessary.
If several listeners participate simultaneously in one test, the seats should be arranged so
that all listeners can see the loudspeakers directly when the screen is taken away.

– 8 – TR 61305-6  IEC:2005(E)
3.3 Electrical requirements
The loudspeakers shall be fed by equipment with characteristics that do not affect the test
results. The system shall consist of a source, level adjustment, and a power amplifier with a
low output impedance and sufficient power (that is, clipping may not occur even at the highest
signal levels). The tone control is to be set to a flat position both on the equipment as well as
on the loudspeakers. Other settings shall be indicated.
Deviations in the flat frequency response shall be less than 0,5 dB in the range from 20 Hz to
20 kHz as measured at the input of the system and at the output of the power amplifier.
3.4 Level setting
The loudspeakers shall be set to provide the same level of volume as measured at an
average listener’s position with a test signal similar to a programme. It has been proven good
practice to feed pink noise to the loudspeakers and set the A-weighted sound level to 75 dB.
NOTE The problem of setting up different loudspeakers by measurement so that reproduction of speech and
music is equal in volume for all loudspeakers cannot be solved completely if the loudspeakers have different
frequency responses. It is only possible to find a practical compromise using such a test signal.
3.5 Listening levels for programmes
The listening levels shall be adjusted so that the loudness is the same, as far as possible, as
the loudness at an average listening position in the original room where the performance was
held.
3.6 Programme material
The programme material should include:
a) speech;
b) chamber music;
c) orchestra music (tutti passages of a large orchestra);
d) solo voice and instrumental accompaniment;
e) entertainment music without significant electro acoustical tampering.
The duration of each unit should be between 60 s and 120 s. The sections should correspond
to musical phrases. The programme material used shall be listed in detail.
3.7 Qualification and number of listeners
The hearing loss of the listeners shall be less than 20 dB in the frequency range of 125 Hz to
8 kHz [1]. Moreover, they should have some form of training or be interested in music, shall
visit concerts regularly and listen to recorded music. The number of listeners shall be not less
than 10.
3.8 Test duration
The duration of one test session should not exceed 1,5 h, whereby a suitable break should be
made after about 0,75 h. The total test duration should not exceed 3 h per day and per
listener.
TR 61305-6  IEC:2005(E) – 9 –
4 Single stimulus ratings
4.1 Test procedure
The purpose of a listening test is to obtain an evaluation of the overall quality of the
loudspeakers. This overall judgement is formed by the various sound characteristics of a
loudspeaker. According to studies made by Gabrielson et al. [2], three independent
characteristics (evaluation aspects) can be found, which can be designated as follows:
• volume;
• definition;
• transparency.
An overall judgement is obtained by combining the evaluations. Since these characteristics
can be judged by comparing with an optimum sound obtained from a comparable original
performance, these loudspeakers can be judged with a single stimulus rating. The result of
t
...