SIST EN 60118-4:2008
(Main)Electroacoustics - Hearing aids -- Part 4: Induction loop systems for hearing aid purposes - Magnetic field strength
Electroacoustics - Hearing aids -- Part 4: Induction loop systems for hearing aid purposes - Magnetic field strength
This international standard is applicable to audio-frequency induction loop systems producing an alternating magnetic field at audio frequencies and intended to provide an input signal for hearing aids operating with an induction pick-up coil. The standard specifies requirements for the field strength in audio-frequency induction loops for hearing aid purposes, which will give adequate signal-to-noise ratio without overloading the hearing aid. The standard also specifies the minimum frequency response requirements for acceptable intelligibility. Methods for measuring the magnetic field strength are specified, and information is given on appropriate measuring equipment (see Annex B), information that should be provided to the operator and users of the system (see Annex C), and other important considerations. The standard does not specify requirements for loop driver amplifiers or associated microphone or audio signal sources, or for the field strength produced by equipment, such as telephone handsets, within the scope of ITU-T P.370.
Akustik - Hörgeräte - Teil 4: Induktionsschleifen für Hörgeräte - Magnetische Feldstärke
Electroacoustique - Appareils de correction auditive -- Partie 4: Systèmes de boucles d'induction utilisées à des fins de correction auditive - Intensité du champ magnétique
S'applique aux systèmes de boucles d'induction audiofréquences qui produisent un champ magnétique alternatif à fréquence acoustique et destinés à produire un signal d'entrée aux appareils de correction auditive fonctionnant avec une bobine d'induction captrice. Cette norme spécifie des exigences concernant l'intensité du champ dans les boucles d'induction utilisées à des fins de correction auditive, qui correspond à un rapport signal sur bruit convenable sans surcharge de l'appareil de correction auditive. Elle spécifie également des exigences concernant la réponse en fréquence minimale pour une intelligibilité acceptable. Les méthodes de mesure de l'intensité du champ magnétique et des renseignements sur l'équipement de mesure approprié (voir Annexe B), ainsi que les renseignements qu'il y a lieu de fournir aux opérateurs et aux utilisateurs du système (voir Annexe C) sont donnés, avec d'autres considérations importantes.
Elektroakustika - Slušni pripomočki - 4. del: Sistemi z indukcijsko zanko za slušne pripomočke - Jakost magnetnega polja (IEC 60118-4:2006)
General Information
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Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 60118-4:2008
01-februar-2008
1DGRPHãþD
SIST EN 60118-4:2002
SIST EN 60118-4:2002/A1:2002
(OHNWURDNXVWLND6OXãQLSULSRPRþNLGHO 6LVWHPL]LQGXNFLMVNR]DQNR]DVOXãQH
SULSRPRþNH-DNRVWPDJQHWQHJDSROMD ,(&
Electroacoustics - Hearing aids - Part 4: Induction loop systems for hearing aid purposes
- Magnetic field strength (IEC 60118-4:2006)
Akustik - Hörgeräte - Teil 4: Induktionsschleifen für Hörgeräte - Magnetische Feldstärke
(IEC 60118-4:2006)
Electroacoustique - Appareils de correction auditive - Partie 4: Systemes de boucles
d'induction utilisées a des fins de correction auditive - Intensité du champ magnétique
(IEC 60118-4:2006)
Ta slovenski standard je istoveten z: EN 60118-4:2006
ICS:
11.180.15 3ULSRPRþNL]DJOXKHRVHEHLQ Aids for deaf and hearing
RVHEH]RNYDURVOXKD impaired people
SIST EN 60118-4:2008 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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EUROPEAN STANDARD
EN 60118-4
NORME EUROPÉENNE
December 2006
EUROPÄISCHE NORM
ICS 17.140.50 Supersedes EN 60118-4:1998 + A1:1998
English version
Electroacoustics -
Hearing aids
Part 4: Induction loop systems for hearing aid purposes -
Magnetic field strength
(IEC 60118-4:2006)
Electroacoustique - Akustik -
Appareils de correction auditive Hörgeräte
Partie 4: Systèmes de boucles d'induction Teil 4: Induktionsschleifen
utilisées à des fins de correction auditive - für Hörgeräte -
Intensité du champ magnétique Magnetische Feldstärke
(CEI 60118-4:2006) (IEC 60118-4:2006)
This European Standard was approved by CENELEC on 2006-11-01. CENELEC 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 Central Secretariat or to any CENELEC 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 CENELEC member into its own language and notified
to the Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, the Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2006 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60118-4:2006 E
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EN 60118-4:2006 - 2 -
Foreword
The text of document 29/604/FDIS, future edition 2 of IEC 60118-4, prepared by IEC TC 29,
Electroacoustics, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 60118-4 on 2006-11-01.
This European Standard supersedes EN 60118-4:1998 + A1:1998.
The purpose of this revision is to provide more information about practical considerations and methods of
measurement. In addition, the requirements for magnetic field strength have been clarified and modified
in the light of practical experience since EN 60118-4:1998 was published. Requirements for the provision
to the end-user of information about the system have been introduced, intended to help to keep systems
working once they have been correctly set up.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2007-08-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2009-11-01
__________
Endorsement notice
The text of the International Standard IEC 60118-4:2006 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:
IEC 60118-1 NOTE Harmonized as EN 60118:1995 + A1:1998 (not modified).
A1
IEC 60268-1 NOTE Harmonized as HD 483.1.S1:1998 (not modified).
IEC 60268-3 NOTE Harmonized as EN 60268-3:2003 (not modified).
IEC 60268-10 NOTE Harmonized as HD 483.10.S1:1993 (not modified).
IEC 61260 NOTE Harmonized as EN 61260:1995 (not modified).
IEC 61672-1 NOTE Harmonized as EN 61672-1:2003 (not modified).
IEC 61938 NOTE Harmonized as EN 61938:1997 (not modified).
__________
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NORME CEI
INTERNATIONALE
IEC
60118-4
INTERNATIONAL
Deuxième édition
STANDARD
Second edition
2006-10
Électroacoustique –
Appareils de correction auditive –
Partie 4:
Systèmes de boucles d’induction
utilisées à des fins de correction auditive –
Intensité du champ magnétique
Electroacoustics –
Hearing aids –
Part 4:
Induction loop systems
for hearing aid purposes –
Magnetic field strength
© IEC 2006 Droits de reproduction réservés ⎯ Copyright - all rights reserved
Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in any
utilisée sous quelque forme que ce soit et par aucun procédé, form or by any means, electronic or mechanical, including
électronique ou mécanique, y compris la photocopie et les photocopying and microfilm, without permission in writing from
microfilms, sans l'accord écrit de l'éditeur. the publisher.
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Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
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PRICE CODE
Commission Electrotechnique Internationale
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
Pour prix, voir catalogue en vigueur
For price, see current catalogue
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60118-4 © IEC:2006 – 3 –
CONTENTS
FOREWORD.7
INTRODUCTION.11
1 Scope.15
2 Normative references .15
3 Terms and definitions .15
4 Suitability of the site for the installation of an audio-frequency induction-loop
system.17
4.1 General .17
4.2 Measurement of magnetic background noise level.17
5 Test signals.19
5.1 General .19
5.2 Speech signals.21
5.3 Pink noise signal .21
5.4 Sinusoidal signal .21
6 Characteristics to be specified, methods of measurement and requirements.23
6.1 General .23
6.2 Amplitude characteristic of the system (or amplifier).23
6.3 Magnetic field strength .25
6.4 Setting up (commissioning) the system.29
6.5 Magnetic noise level due to the system .31
6.6 Frequency response of the magnetic field .31
6.7 Useful magnetic field volume.33
Annex A (informative) Small area systems .37
Annex B (informative) Measuring equipment .39
Annex C (informative) Provision of information .45
Annex D (informative) Measuring speech signals .51
Annex E (informative) Basic theory and practice of audio-frequency induction-loop
systems .53
Annex F (informative) Calibration of field-strength meters.77
Bibliography.81
Figure C.1 – Graphical symbol No.10: Inductive coupling .47
Figure E.1 – Perspective view of a loop, showing the magnetic field vector paths .55
Figure E.2 – Variation of the vertical field strength with position, due to a current in a
rectangular loop, with perpendicular distance from the loop plane, as parameter .57
Figure E.3a – Geometry of the loop and positions of measurement of the field patterns
shown in Figure E.3b .59
Figure E.3b – Patterns of the vertical and horizontal components of the magnetic field
due to current in a horizontal rectangular loop, at points in a plane above or below the
loop plane.59
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60118-4 © IEC:2006 – 5 –
Figure E.4 – Field patterns of the vertical component of the magnetic field of a
horizontal loop .61
Figure E.5 – Field patterns of the vertical component of the magnetic field of a
vertical loop .63
Figure E.6 – Perspective view of the variation of the vertical field strength level
at an optimum height above a horizontal rectangular loop.65
Figure E.7a – Directional response of the magnetic pick-up coil of a hearing aid;
linear amplitude scale .65
Figure E.7b – Directional response of the magnetic pick-up coil of a hearing aid;
decibel amplitude scale.67
Figure F.1 – Triple Helmholtz coil for calibration of meters.77
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60118-4 © IEC:2006 – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTROACOUSTICS – HEARING AIDS –
Part 4: Induction loop systems for hearing aid purposes –
Magnetic field strength
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
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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
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
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6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
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expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
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.
International Standard IEC 60118-4 has been prepared by IEC technical committee 29:
Electroacoustics.
This second edition cancels and replaces the first edition published in 1981 and its
Amendment 1 (1998), and constitutes a technical revision. The purpose of this revision is to
provide more information about practical considerations and methods of measurement. In
addition, the requirements for magnetic field strength have been clarified and modified in the
light of practical experience since the first edition was published. Requirements for the
provision to the end-user of information about the system have been introduced, intended to
help to keep systems working once they have been correctly set up.
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60118-4 © IEC:2006 – 9 –
The text of this standard is based on the following documents:
FDIS Report on voting
29/604/FDIS 29/613/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 60118 series, published under the general title Electroacoustics –
Hearing aids, can be found on the IEC website.
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.
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60118-4 © IEC:2006 – 11 –
INTRODUCTION
Audio-frequency induction loop systems are widely used to provide a means for hearing aid
users, whose hearing aids are fitted with induction pick up coils, to minimise the problems of
listening when at a distance from a source of sound, shielded from the person speaking by a
protective window, and/or in a background noise. Background noise and distance are two of
the main causes of hearing aid users being unable to hear satisfactorily in other than face-to-
face quiet conditions. Induction loop systems have been widely installed in churches, theatres
and cinemas, for the benefit of hearing-impaired people. The use of induction loop systems
has been extended to many transient communication situations such as ticket offices, bank
counters, drive-in/drive-through service locations, lifts/elevators etc. The widespread provision
of telephone handsets that provide inductive coupling to hearing aids is another significant
application, where ITU-T Recommendation P370 “Coupling hearing aids to telephone sets”
applies.
Transmission of an audio-frequency signal via an induction loop system can often establish
an acceptable signal-to-noise ratio in conditions where a purely acoustical transmission would
be significantly degraded by reverberation and background noise.
One form of audio frequency induction loop system comprises a cable installed in the form of
a loop usually around the perimeter of a room or area in which a group of hearing impaired
persons wish to listen. The cable is connected via an amplifier to a microphone system or
other source of audio signal, such as a radio receiver, CD player etc. The amplifier produces
an audio-frequency electric current in the induction loop cable, causing a magnetic field to be
produced inside the loop. The design and implementation of the induction loop is determined
by the construction of the building in which it is installed, particularly by the presence of large
amounts of iron, steel or aluminium in the structure. In addition the layout and position of
electrical cables and equipment may generate high levels of background audio frequency
magnetic fields that may interfere with the reception of the loop signal.
Another form of induction loop system employs a small loop, intended for communication with
a hearing-aid user in its immediate vicinity. Examples are: neck loops, ticket-counter systems,
self-contained 'portable' systems and chairs incorporating induction loops. (See Annex A)
The pick-up device for an audio-frequency induction loop system is usually a personal hearing
aid, of a type fitted with a pick-up coil; however, special induction loop receivers may be used
in certain applications.
The use of personal hearing aids as loop system receivers enables the wearers of these aids
to take advantage of induction loop signal transmission wherever such loops are provided,
particularly in public places. For this advantage to be most effective it is necessary for a
standard value of magnetic field strength to be adopted, thus allowing a corresponding
adjustment of the sensitivity of the pick-up coil in the hearing aid. The magnetic field strength
has been chosen so that:
– it is high enough to produce an acceptable signal-to-noise ratio over background magnetic
noise from power installations etc.;
– it is not so high as to cause overloading of the hearing aid.
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60118-4 © IEC:2006 – 13 –
The lower limit of magnetic field strength is governed by the expected level of background
magnetic noise, measurements of which have been made in a number of homes, churches,
schools, theatres, etc., in order to determine typical values. Measurements have also been
made on hearing aids, to determine an acceptable range of input levels and on which the
higher limit is based. See IEC 60118-1:1995, amendment 1:1998.
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60118-4 © IEC:2006 – 15 –
ELECTROACOUSTICS – HEARING AIDS –
Part 4: Induction loop systems for hearing aid purposes –
Magnetic field strength
1 Scope
This international standard is applicable to audio-frequency induction loop systems producing
an alternating magnetic field at audio frequencies and intended to provide an input signal for
hearing aids operating with an induction pick-up coil.
The standard specifies requirements for the field strength in audio-frequency induction loops
for hearing aid purposes, which will give adequate signal-to-noise ratio without overloading
the hearing aid. The standard also specifies the minimum frequency response requirements
for acceptable intelligibility.
Methods for measuring the magnetic field strength are specified, and information is given on
appropriate measuring equipment (see Annex B), information that should be provided to the
operator and users of the system (see Annex C), and other important considerations.
The standard does not specify requirements for loop driver amplifiers or associated
microphone or audio signal sources, or for the field strength produced by equipment, such as
telephone handsets, within the scope of ITU-T P.370.
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.
None.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
reference magnetic field strength level
the 0 dB reference for magnetic field strength levels is 400 mA/m
NOTE This is measured as specified in 6.3.1 and 6.3.6.
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60118-4 © IEC:2006 – 17 –
3.2
long-term average magnetic field strength level
long-term average level of the magnetic field strength produced by the system
NOTE 1 In the previous edition of this standard, this term was used to define the reference for magnetic field
strength level measurements, but it is difficult to measure, so the maximum short-term magnetic field strength
(see 6.3.1) is used in this edition for that purpose. This does NOT represent a technical change to the
requirements for field strength. See also Annex D.
NOTE 2 'Long term' is not equivalent to 'S' time weighting as defined in IEC 61672-1. The L is a good
eq,60
s
indication for the long-term average for some speech signals.
NOTE 3 An acoustic input sound pressure level of 70 dB and long-term average field strength of 100 mA/m in a
hearing aid are assumed to give the same acoustic output level. See IEC 60118-1:1999, Clause 6.
3.3
useful magnetic field volume
volume within which the system provides hearing-aid users with a signal of acceptable quality
(see 6.7).
NOTE 1 In the previous edition of this standard, the concept of 'specified magnetic field area' was defined,
because that edition did not consider the very important 'height' dimension (the perpendicular distance between the
hearing aid pick-up coil and the plane of the loop). See Annex E.
NOTE 2 The base area of the useful magnetic field volume is often different from the plan area of the induction
loop.
4 Suitability of the site for the installation of an audio-frequency induction-
loop system
4.1 General
NOTE 1 This clause is included at this place in the text because it should be considered before a system is
installed and its text has to precede 6.4 for clarity.
It may not be possible to obtain acceptable conditions for an induction loop system in all
places where it is desirable. It is therefore necessary in the planning stage to examine a
proposed location with respect to the following conditions:
• the magnetic noise level from electric installations, e.g. heating systems in the floor or
roof, the electrical control of lighting systems (especially in theatres);
• the influence of magnetic and electrically-conducting materials in the structure in which
the loop is intended to be installed;
• the presence of other induction loop systems in the neighbourhood, the signals of which
may interfere with that of the planned loop system.
NOTE 2 Techniques exist to reduce radiation outside an induction loop, but previously-installed systems may not
be so designed.
4.2 Measurement of magnetic background noise level
4.2.1 Method of measurement
Measurements of magnetic noise levels shall be performed by using an A-weighting network
in the measuring instrument. The measured values, expressed as the maximum average
short-term (0,125 s averaging time) of the r.m.s. values of the magnetic field strength,
measured with a pick-up coil whose magnetic axis is vertical (unless otherwise specified, see
6.1), shall be expressed as levels in dB referred to the reference magnetic field strength level
(see 3.1).
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60118-4 © IEC:2006 – 19 –
The induction loop system shall be switched off. The magnetic background noise level shall
be measured at a sufficient number of points in the useful magnetic field volume. The
selection of points may be randomly distributed, but should be influenced by the height range
of the users (normally measurement height of 1,2 m for seated listeners and 1,7 m for
standing listeners should be used), specific seating requirements, physical layout of the
location and potential influence from metal and interfering signals.
NOTE It is useful to listen to the noise, to form a subjective impression of its spectrum, and thus the likely
disturbing effect on listeners.
4.2.2 Recommended maximum magnetic noise levels
Ideally, the difference between the reference magnetic field strength level and the A-weighted
magnetic background noise level, which for clarity is referred to as 'reference signal-to-noise
ratio' in this standard, should be greater than 47 dB. This value is appropriate in situations
where the aesthetic value of the speech is important and the background acoustic noise level
is very low, i.e. in theatres and similar locations. Such low levels of magnetic (and acoustic –
see Note 2) noise may not always be present. In cases where communication takes priority
over aesthetic considerations, a higher magnetic noise level may be tolerable. It should also
be considered that high levels of magnetic background noise can be tiring and thus should
only be tolerated where the communication is of a short and essential nature. The actual
audible impact of the interfering signal should then be considered in assessing whether the
overall benefit of the system to hearing-aid users is preferable to the absence of a loop
system or the use of an alternative technique requiring a special receiver (i.e. infra-red or
radio).
NOTE 1 If such a system is used it can only be used with headphones because the magnetic background noise is
picked up by a hearing aid switched to ‘T’, as is necessary if a neck loop is used. The headphones should be
suitable for hearing aid wearers.
If the magnetic noise has no significant undesirable tonal quality or is mostly at low
frequencies, then a higher level of interfering signal may be acceptable. For example, a
reference signal-to-noise ratio as low as 22 dB may be tolerable. If the actual ratio is less
than 32 dB, this shall be reported and consideration given to remedial measures.
NOTE 2 Hearing-aid users are exposed to acoustic noise at the site, as well as magnetic noise. There is no point
in requiring a magnetic noise level far lower than the acoustic noise level as perceived by hearing-aid users.
5 Test signals
5.1 General
It is possible to use several different types of test signal for the setting-up and measurement
of the frequency mid-band value (in case of doubt, the average value over the octave band
centred on 1 kHz) and the frequency response of the magnetic field strength. However, some
signals are not suitable for some purposes, and the suitability depends on the amplitude
characteristic of the amplifier in the system (see 6.2). The test signal specified by the
amplifier manufacturer shall be used, unless the use of a different signal can be justified.
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60118-4 © IEC:2006 – 21 –
5.2 Speech signals
5.2.1 Live speech signals
Live speech is suitable only for use as a
...
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