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IEC TR 63079
Edition 1.0 2017-04
TECHNICAL
REPORT
colour
inside
Code of practice for hearing-loop systems (HLS)
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IEC TR 63079
Edition 1.0 2017-04
TECHNICAL
REPORT
colour
inside
Code of practice for hearing-loop systems (HLS)
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.140.50 ISBN 978-2-8322-4154-7
– 2 – IEC TR 63079:2017 IEC 2017
CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 10
2 Normative references . 10
3 Terms, definitions, signs and symbols . 10
3.1 Terms and definitions . 10
3.2 Signs and symbols . 12
3.2.1 Symbol for an induction-loop . 12
3.2.2 Symbol for multiple loops . 12
3.2.3 Sign for display in premises where an HLS is installed and for HLS
equipment identification . 13
3.2.4 Identification of areas where reception of the HLS is not satisfactory . 13
4 General . 14
4.1 How to use this document . 14
4.1.1 Persons addressed . 14
4.1.2 Objectives . 14
4.2 Specialist advice . 15
4.3 Safety aspects . 15
4.4 Conforming to existing performance documents . 15
5 Technical advice . 15
5.1 Complying with this document . 15
5.2 Seeking technical advice . 15
5.3 The nature of the advice . 16
5.4 Professional (consultancy) advice . 16
6 Purpose of the system . 16
7 Choosing the system supplier . 16
7.1 General . 16
7.2 Approaching a contractor . 17
7.3 Approaching a manufacturer of HLS equipment . 17
7.4 Approaching a specialist consultant . 17
8 Contractual provisions . 17
8.1 Performance specification . 17
8.2 Verifying that the completed system delivers its intended performance . 17
8.3 Arbitration . 18
9 Classification of systems . 18
10 Design . 20
10.1 General . 20
10.2 Symbols . 20
10.3 Basic theory . 21
10.3.1 Production of a magnetic field . 21
10.3.2 Directional pattern of the magnetic field . 22
10.3.3 Uniformity of the magnetic field strength . 26
10.3.4 Reference points for magnetic field strength . 26
10.3.5 Relationship between the requirements of IEC 60118-4 and the
characteristics of hearing aids and speech signals . 27
10.3.6 Impedance of the loop . 28
10.3.7 Selection of the method of driving the loop . 29
10.3.8 Current-driven loop . 29
10.3.9 Voltage-driven loop . 30
10.3.10 Voltage-driven loop with high-level equalization . 31
10.3.11 Voltage-driven loop with low-level equalization . 33
10.3.12 Use of transformers . 33
10.3.13 Effects of building construction . 34
10.3.14 Electromagnetic compatibility (EMC) . 35
10.3.15 Tone signals . 37
10.3.16 Equalization, other than for compensating loop impedance
characteristics . 37
10.3.17 Multiple loops . 37
10.3.18 Protection of loop conductors . 40
10.3.19 Automatic gain control (AGC), compression, limiting, noise gating and
voice control . 40
10.3.20 Signal-to-noise ratio . 41
10.3.21 HLS for purposes other than assisted hearing . 42
10.4 System components . 42
10.4.1 Final amplifiers . 42
10.4.2 Preamplifiers and mixers . 42
10.4.3 Signal sources . 43
10.5 Objective measurement of intelligibility . 50
10.6 Safety and reliability considerations . 51
10.7 Designing for monitoring and maintenance . 51
10.8 External factors . 51
10.8.1 Magnetic noise interference . 51
10.8.2 Effect of metal in the building . 52
10.9 Magnetic field overspill . 52
10.10 The role of the system designer in commissioning . 52
11 Responsibility of the installer . 52
12 Installation practices and workmanship . 54
13 Inspection and testing of wiring . 55
14 Commissioning . 56
15 Documentation . 57
16 Certification . 58
17 Acceptance. 59
18 Verification . 60
19 Owner responsibilities . 60
19.1 Signage . 60
19.2 User feedback . 61
19.3 Staff training . 61
20 Operation and maintenance . 61
20.1 General . 61
20.2 Routine testing . 61
20.3 Inspection and servicing . 62
20.4 Non-routine attention . 63
20.5 Special inspection on appointment of a new maintenance organization . 63
20.6 Arrangements for repair of faults or damage . 63
– 4 – IEC TR 63079:2017 IEC 2017
20.7 Modifications to the system .
...