SIST ETS 300 381 E1:2003

SLOVENSKI STANDARD
SIST ETS 300 381 E1:2003
01-december-2003
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Telephony for hearing impaired people; Inductive coupling of telephone earphones to
hearing aids
Ta slovenski standard je istoveten z: ETS 300 381 Edition 1
ICS:
11.180.15 3ULSRPRþNL]DJOXKHRVHEHLQ Aids for deaf and hearing
RVHEH]RNYDURVOXKD impaired people
33.050.10 Telefonska oprema Telephone equipment
SIST ETS 300 381 E1:2003 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ETS 300 381 E1:2003

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SIST ETS 300 381 E1:2003
EUROPEAN ETS 300 381
TELECOMMUNICATION December 1994
STANDARD
Source: ETSI TC-TE Reference: DE/TE-04091
ICS: 33.020, 33.040.40
Telephony, hearing aids, inductive coupling, PWSN
Key words:
Telephony for hearing impaired people;
Inductive coupling of telephone earphones
to hearing aids
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
F-06921 Sophia Antipolis CEDEX - FRANCE
Postal address:
650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
Office address:
c=fr, a=atlas, p=etsi, s=secretariat - secretariat@etsi.fr
X.400: Internet:
Tel.: +33 92 94 42 00 - Fax: +33 93 65 47 16
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the
foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1994. All rights reserved.
New presentation - see History box

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ETS 300 381: December 1994
Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Editing and Committee Support Dept." at the address shown on the title page.

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ETS 300 381: December 1994
Contents
Foreword .5
1 Scope .7
2 Normative references.7
3 Definitions and abbreviations .7
3.1 Definitions .7
3.2 Abbreviations .7
4 Introduction.8
4.1 General .8
4.2 Background.8
5 Requirements.8
5.1 Magnetic field strength level .9
5.2 Linearity of the magnetic field strength .9
5.3 Frequency characteristics.9
6 The probe coil.11
6.1 Dimensions .11
6.2 Calibration of probe coil .11
6.3 Distortion.11
6.4 Connecting leads for probe coil .12
7 Test procedures .12
7.1 Calibration of receive sound pressure level.12
7.2 Measurement of the magnetic field strength level .13
7.3 Measurement of the linearity of the magnetic field strength .13
7.4 Measurement of frequency characteristics.13
Annex A (normative): Packaging, labelling and user instructions .15
A.1 Packaging and labelling .15
A.2 User instructions.15
Annex B (informative): Step-by-step measurement procedures.15
Annex C (informative): Symbol indicating facilities for the hearing impaired.16
Annex D (informative): Typical characteristics of probe coil .17
Annex E (normative): Calibration of the probe coil.17
Annex F (informative): Components of the inductive field .18
Annex G (informative): Bibliography.19
History.20

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ETS 300 381: December 1994
Foreword
This European Telecommunication Standard (ETS) has been produced by the Terminal Equipment (TE)
Technical Committee, in co-operation with the Human Factors (HF) Technical Committee, of the
European Telecommunications Standards Institute (ETSI).
Several administrations and operating agencies have expressed the opinion that it would be acceptable if
this ETS were to be made mandatory for public telephones and wherever telephones are installed on the
basis of safety, e.g. in lifts. It would not be expected to be mandatory in all countries for all telephone
terminals. However, if such a facility is made available, it should conform to the requirements of this ETS,
and labels and literature advertising the facility should not be related to a particular product unless it does
in fact so comply.
Annexes A and E of this ETS are normative while annexes B to D and annexes F and G are informative.
Proposed transposition dates
Date of latest announcement of this ETS (doa): 31st March 1995
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 30th September 1995
Date of withdrawal of any conflicting National Standard (dow): 30th September 1995

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ETS 300 381: December 1994
1 Scope
This ETS applies to all telephones having supra-aural earphones (see ITU-T Recommendation P.57 [4])
that can be connected to the Public Switched Telephone Network (PSTN) or Integrated Services Digital
Network (ISDN), which are intended for direct application to the ear (e.g. traditional handsets, operators'
headsets) and which provide, at the earphone, a magnetic field for coupling to hearing aids. It specifies
the level linearity and frequency dependence of the magnetic field strength produced by the handset and
characteristics for the calibrated probe coil.
Handsfree or loudspeaking devices are outside the scope of this ETS.
2 Normative references
This ETS 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 ETS only when incorporated in it by amendment or revision. For undated references the latest
edition of the publication referred to applies.
[1] ITU-T Recommendation P.37 (1993): "Coupling hearing aids to telephone sets".
[2] ITU-T Recommendation P.64 (1993): "Determination of sensitivity/frequency
characteristics of local telephone systems".
[3] CCITT Handbook on Telephonometry, ITU, Geneva (1992).
[4] ITU-T Recommendation P.57 (1993): "Artificial ears".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of this ETS, the following definitions apply:
level of magnetic field strength: The maximum value of the magnetic field strength is given in
subclause 5.1 and is measured in accordance with subclause 7.1. The units are Amperes per metre
(A/m).
permissible range: The range into which the measured level of the magnetic field strength needs to fall
to comply with this ETS.
plane of measurement: A plane parallel to the earcap plane at a distance of 10 mm.
preferred range: The range of magnetic field strength likely to be required for satisfactory performance by
hearing aids designed primarily for coupling to magnetic loops often installed in auditoria.
sound pressure level: Acoustic sound pressure level is expressed in decibels relative to 1 Pascal (or
dBPa).
3.2 Abbreviations
For the purposes of this ETS, the following abbreviations apply:
ISDN Integrated Services Digital Network
LRGP Loudness Rating Guard-ring Position
PSTN Public Switched Telephone Network
TE Terminal Equipment

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4 Introduction
4.1 General
It is recognised that there is a sizeable proportion of telephone users that have difficulty in conversing over
a telephone connection due to hearing loss. To alleviate these difficulties special means have been
provided in many national systems to enable hearing impaired users to couple their hearing aids
inductively to the telephone receiver, and a number of national/international specifications define
characteristics for this form of coupling. This ETS addresses the requirements for successful inductive
coupling of hearing aids to telephone sets.
Furthermore, it is also recognised that many hearing impaired users are able to have satisfactory
telephone conversations while coupling their hearing aids acoustically to the telephone receiver, or even
using the telephone handset without a hearing aid. This latter situation is possible due to the fact that,
under good conditions, a telephone connection can be louder than a face-to-face conversation over a 1
metre air path by up to 30 dB.
The inclusion of inductive coupling does not reduce or replace existing technical standards that apply to a
handset. Inductive coupling can be combined with other additional functionality, such as amplification or
extra earpieces, provided specifically for people with special needs.
Provision of additional amplification in the mouth-to-ear path can greatly increase the proportion of
telephone conversations involving hearing impaired users that are rated as "good". A separate ETSI
Standard is planned to cover this form of coupling and it is also addressed by ITU-T Recommendation
P.37 [1]. Certain national standards also exist to enable direct electrical connection of hearing aids to
telephone apparatus. It is hoped that this form of coupling will be covered in a future ETSI standard.
4.2 Background
Magnetic induction systems incorporated in telephone handsets generate an alternating magnetic field
with special characteristics which make the field detectable by hearing aids equipped with induction
pick-up coils.
Reception of an audio-frequency signal via an induction pick-up coil can often allow an acceptable signal-
to-noise ratio to be achieved in cases where the acoustical reception would otherwise be degraded by
background noise.
The magnetic field strength, which enables induction pick up coils in hearing aids to function effectively,
shall be high enough to produce an acceptable signal to noise ratio but not so high as to cause
overloading of the hearing aid.
The value of the magnetic field strength given in this ETS has been chosen so that these requirements
are met as far as possible.
Measurement methods used in this ETS are in accordance with those given in ITU-T Recommendations
P.37 [1] and P.64 [2] plus the CCITT Handbook on Telephonometry [3].
NOTE: Care should be taken when designing hearing aids to include sufficient immunity to
radio frequency interference to avoid disturbances arising from the detection of radio
signals emitted by cordless and mobile telephones.
5 Requirements
The following requirements in respect of magnetic field strength as a function of frequency shall be met at
all settings of the volume control, if provided. These requirements concern the sensitivity at 1 000 Hz, the
frequency response and the linearity at 1 000 Hz as a function of the earphone sound pressure level
measured with an artificial ear conforming to ITU-T Recommendation P.57 [4], Type 1.
NOTE: In respect of low acoustic impedance earphones, when the artificial ear according to
ITU-T Recommendation P.57 [4], Type 3.2 is validated then the level definition will
need to be reviewed.

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5.1 Magnetic field strength level
The level of the magnetic field strength at 1 000 Hz when measured in accordance with subclause 7.2
shall be:
Permissible range: - 17 dB to - 30 dB relative to 1 A/m,
Preferred range: - 17 dB to - 25 dB relative to 1 A/m,
for an electrical drive to the telephone that gives a sound pressure level of - 14 dBPa at the artificial ear.
NOTE: Hearing aids with magnetic pick-up coils primarily intended for coupling to magnetic
loops in auditoria in accordance with IEC Publication 118-4, are likely to require a field
strength in the
...