IEC 60118-4:2014/AMD1:2017

IEC 60118-4 ®
Edition 3.0 2017-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
A MENDMENT 1
AM ENDEMENT 1
Electroacoustics – Hearing aids –
Part 4: Induction-loop systems for hearing aid purposes – System performance
requirements
Électroacoustique – Appareils de correction auditive –
Partie 4: Systèmes de boucles d'induction utilisées à des fins de correction
auditive – Exigences de performances système

IEC 60118-4:2014-12/AMD1:2017-11(en-fr)

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IEC 60118-4 ®
Edition 3.0 2017-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
A MENDMENT 1
AM ENDEMENT 1
Electroacoustics – Hearing aids –

Part 4: Induction-loop systems for hearing aid purposes – System performance

requirements
Électroacoustique – Appareils de correction auditive –

Partie 4: Systèmes de boucles d'induction utilisées à des fins de correction

auditive – Exigences de performances système

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.140.50 ISBN 978-2-8322-4970-3

– 2 – IEC 60118-4:2014/AMD1:2017
IEC 2017
FOREWORD
This amendment has been prepared by committee IEC technical committee 29:
Electroacoustics.
The text of this amendment is based on the following documents:
CDV Report on voting
29/952/CDV 29/961/RVC
Full information on the voting for the approval of this amendment can be found in the report
on voting indicated in the above table.
The committee has decided that the contents of this amendment and the base publication will
remain unchanged until the stability date indicated on the IEC website 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• withdrawn,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.
_____________
3 Terms and definitions
Add, after 3.3, the following new term and definition:
3.4
automatic gain control
AGC
process or device by which the gain of an amplifier is controlled by the level of the output
signal so as to reduce changes in this level as compared with the changes in the input signal
Note 1 to entry: Frequently, automatic gain control is used to keep the output signal level nearly constant.
Note 2 to entry: There is a consistent but more general definition in IEC 60118-7, but this standard may have a
limited future, so the IEV definition is preferred.
9 Small-volume systems
Replace the existing text of Clause 9 by the following new text:
9.1 Definition of measurement points
For small-volume systems, it is possible and necessary in some applications to specify in this
standard the positions of the measurement points. For this reason, points are specified for
both disabled refuge and similar call points, and for counter systems. However, where these
suggested measurement points are not practical, the "useful magnetic field volume" method

IEC 2017
as defined in 9.4 can be applied, the details of which should be agreed as part of the
contractual requirements.
9.2 Disabled refuge and similar call-points
Measurements shall be made at the six points specified in Figures 2 a) and b). The reference
point (or line) is the face or surface of the call point, intercom, or help point closest to the
user, and is not necessarily the location of the magnetic field source.
The semi-circular layout is suitable for small magnetic field sources and the rectangular layout
is suitable for vertical or floor loop sources. Only one of the methods shall be used for a given
system.
NOTE An offset (shown as l in Figure 2) between the reference point (or line) and the position of the magnetic
field source promotes evenness of field pattern over the area where people are expected to stand.

– 4 – IEC 60118-4:2014/AMD1:2017
IEC 2017
l
l
45° 45°
IEC
Key
1 magnetic field source
2 reference point
3 area where people are expected to stand
l offset
l inner radius: 300 mm
l +l outer radius: 500 mm
2 3
a) Magnetic field source of small dimensions

l
= =
3 3
= =
l
IEC
Key
1 magnetic field source (vertical loop)
2 reference line
3 area where people are expected to stand
l offset
l 300 mm
l 200 mm
l 424 mm
l 700 mm
b) Larger magnetic field source
Figure 2 – Measurement points for disabled refuge
and similar call-points
l
l l l
3 2 1
IEC 2017
The six measurement points are required at 1,2 m and 1,7 m (see Figure 3 b)), but there is no
requirement to measure at 1,45 m.
9.3 Counter systems
Measurements shall be made at the points specified in Figures 3 a) and b). The reference
point is the face or surface of the counter closest to the user, and is not necessarily the
position of the magnetic field source. For counter systems, there is often a requirement to
control overspill to an adjacent counter position. Controlling this overspill is likely to be a
significant factor in design, and as such may result in a compromise of evenness of field over
the area where people are expected to stand.
NOTE 1 It is not necessary to reduce the magnetic spill between counter positions below a level comparable with
the acoustic spill. A difference greater than 20 dB between equivalent positions at the two counters is normally
enough.
NOTE 2 The boundaries of the area where people are expected to stand cannot be standardized as they depend
on the building layout and counter design.
NOTE 3 For vertical loops, an offset (shown as l in Figure 3) between the reference point and the position of the
loop promotes evenness of field pattern over the area where people are expected to stand, but reduces the
effectiveness of overspill control to the next counter position.

– 6 – IEC 60118-4:2014/AMD1:2017
IEC 2017
l l
1 2
3 3
l l
4 5
IEC
Key
1 magnetic field source
2 reference line
3 area where people are expected to stand (outside the dotted semi-circle)
l 300 mm
l 300 mm
l offset
l 150 mm
l 150 mm
a) Plan view
1 2
IEC
Key
1 magnetic field source
2 reference line
3 floor level
250 mm
l
l 250 mm
l 1 200 mm
b) Side elevation
Figure 3 – Measurement points for a counter system
l l l
3 2 1
l
IEC 2017
Measurements at the three points shown in the plan view are required at 1,2 m, 1,45 m and
1,7 m.
9.4 Useful magnetic field volume method
Requirements based on a useful magnetic field volume, as described in 8.4, may be used in
place of the methods in 9.2 or 9.3, if agreed contractually. The useful magnetic field volume
shall be defined, and a set of representative measurement points determined which are
distributed so as to ensure that the requirements are met in that volume (3-dimensional
space). Measurements shall be made at these representative points, whose positions shall be
recorded with the results of the measurements.
As a minimum, the requirements shall be met for at least one position at each of the heights
defined in 9.2 and 9.3 in the area where people are expected to stand.
All notes in 9.2 and 9.3 are applicable where appropriate.
9.5 Requirements
The magnetic field strength level at all measurement points specified in 9.2, 9.3 or 9.4 shall
be ±6 dB ref. 400 mA/m, measured according to 8.2. At one point at least, it shall be at least
0 dB ref. 400 mA/m. In addition, the requirements in 8.3.7 shall be met at all measurement
points.
The magnetic field strength level shall not be above +8 dB ref. 400 mA/m in the area where
people are expected to stand.
NOTE 1 This high field strength is inevitable for a simple vertical loop of practicable dimensions. If the signal is
too loud or distorted, the user can move a short distance further away from the source of the magnetic field.
NOTE 2 Clauses 4 and 7 deal with the subject of magnetic background noise level. It is not practicable to specify
a requirement, as this might rule out the provision of a system that would be at least helpful to users.
10 Setting up (commissioning) the system
Replace the existing text by the following new text:
10.1 Procedure
The commissioning procedure shall include a test with the sound sources (talker, etc.) in their
normal positions with respect to the system microphone(s), and with any other sources, such
as a CD player. Measurements shall be made to check that the controls of the amplifier, etc.,
are set so that the magnetic field strength specified in 8.2.7 is achieved. If the amplifier has a
gain control preceding the AGC stage, and an indicator that the AGC is operating, it is
normally sufficient to set the control so that t
...