Amendment 1 - Electroacoustics - Hearing aids - Part 4: Induction-loop systems for hearing aid purposes - System performance requirements

Amendement 1 - Electroacoustique - Appareils de correction auditive - Partie 4: Systèmes de boucles d'induction utilisées à des fins de correction auditive - Exigences de performances système

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Status
Published
Publication Date
08-Nov-2017
Technical Committee
Drafting Committee
Current Stage
PPUB - Publication issued
Start Date
24-Nov-2017
Completion Date
09-Nov-2017
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IEC 60118-4:2014/AMD1:2017 - Amendment 1 - Electroacoustics - Hearing aids - Part 4: Induction-loop systems for hearing aid purposes - System performance requirements
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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

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

---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
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



Warning! Make sure that you obtained this publication from an authorized distributor.

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® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

---------------------- Page: 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

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IEC 60118-4:2014/AMD1:2017 – 3 –
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
1
field source promotes evenness of field pattern over the area where people are expected to stand.

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– 4 – IEC 60118-4:2014/AMD1:2017
IEC 2017
1
2
l
2
l
3
45° 45°
3

IEC
Key
1 magnetic field source
2 reference point
3 area where people are expected to stand
l offset
1
l inner radius: 300 mm
2
l +l outer radius: 500 mm
2 3
a) Magnetic field source of small dimensions

1
2
l
4
= =
3 3
= =
l
5
IEC

Key
1 magnetic field source (vertical loop)
2 reference line
3 area where people are expected to stand
l offset
1
l 300 mm
2
l 200 mm
3
l 424 mm
4
l 700 mm
5
b) Larger magnetic field source
Figure 2 – Measurement points for disabled refuge
and similar call-points
l
1
l l l
3 2 1

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IEC 60118-4:2014/AMD1:2017 – 5 –
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
3
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.

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– 6 – IEC 60118-4:2014/AMD1:2017
IEC 2017
1
l l
1 2
2
3 3
l l
4 5
3

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
1
l 300 mm
2
l offset
3
l 150 mm
4
l 150 mm
5
a) Plan view
1 2
3
IEC

Key
1 magnetic field source
2 reference line
3 floor level
250 mm
l
1
l 250 mm
2
l 1 200 mm
3
b) Side elevation
Figure 3 – Measurement points for a counter system
l l l
3 2 1
l
3

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IEC 60118-4:2014/AMD1:2017 – 7 –
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 the indication specified by the manufacturer is
achieved. The reference speech signal as defined in 6.3.3.3 can also be used for a more
objective test, but as in all cases it should not be necessary to adjust the 'loop drive' control
(gain control after the AGC stage) of the amplifier. It is desirable that a small number of
hearing-aid users should be present when a system is being set up for the first time or after
extensive changes, to check that the subjective results are consistent with the measurements.
It is important to check these hearing aid users for correct operation of their aids, and to
ensure that they actually understand what they are supposed to be listening to. It is essential
that the trained persons(s) specified in Clause E.5 are present, with the receivers they will
use for normal system checking.
NOTE Some hearing aid users set their volume controls much too high, and some older hearing aids tended to
overload at a rather low field strength. Where significant variations of opinion are experienced between hearing aid
users, on the performance of a system, it could be necessary to check the settings of the aids.

---------------------- Page: 9 ----------------------
– 8 – IEC 60118-4:2014/AMD1:2017
IEC 2017
10.2 Requirements
The maximum value of the magnetic field strength obtained from the reference speech signal
(see 6.3.3.3) shall normally be 400 mA/m, measured with a meter as specified in 6.1.
For the reference signal and all real sound sources, the measured value depends on the
characteristics of the AGC circuit as well as the signal source itself, and as a result the
measured r.m.s levels are likely to deviate from the target value. Provided the measurement
time is long enough to observe true maximum levels, the system should usually achieve ±3 dB
ref 400 mA/m (283 mA/m to 566 mA/m).
If a field strength of 400 mA/m ± 3 dB is not achieved with real signals, the measurement shall
be repeated using the signal specified in 6.3.3.3. If the requirement is still not met, the system
specification and the set-up procedure given in 4.1 shall be reviewed, to determine whether
the system as a whole, and the amplifier, have been correctly specified.
10.3 Amplifier overload at the upper bound of maximum power bandwidth
10.3.1 Explanation
If frequency-response correction is applied to the amplifier in order to compensate for metal
loss, even if the amplifier is capable of producing the required maximum magnetic field
strength at 1,0 kHz, it might be overloaded (in terms of output voltage or current capability) at
a higher frequency.
The maximum power bandwidth required for a system is dependent on the signal to be used
in the application. For speech, the upper bound is generally considered to be 1,6 kHz. For
systems which are designed to reproduce music this figure may need to be increased. For
systems which are only designed for brief or transient use (and so fatigue is not a factor),
1,25 kHz may be enough.
This test is for evaluating the capability when delivering real programme signals, but a simple
test using a sinewave signal causes the amplifier to draw an unusually high current from its
power supply, and as such is considered inappropriate. A test using a reduced current at
approximately double the desired maximum power frequency yields more representative
results, as it results in a more realistic power supply current.
10.3.2 Methods of test
Apply a sine wave signal at 1,0 kHz and adjust its level so that a magnetic field strength 7 dB
less than the required value is obtained at a given point. Apply this signal only for the shortest
practicable time, in order to prevent overheating of the amplifier. Measure the voltage across
the loop. Increase the input frequency, without changing its level, until the voltage across the
loop is doubled, or the relevant test frequency specified in Table 4 is reached, whichever is
the greater frequency.
NOTE 1 The magnetic field strength is intentionally increased by the frequency-response compensation.
NOTE 2 The reduction in level of 7 dB is used so that systems on the threshold of clipping do not fail the test.
Table 4 – Programme material and test frequency
Typical system programme Upper frequency bound of the Test
material maximum power bandwidth frequency
Transient use speech 1,25 kHz 2,5 kHz
e.g. small volume systems
Speech (default) 1,6 kHz 3,15 kHz
Music 2,0 kHz 4,0 kHz

---------------------- Page: 10 ----------------------
IEC 60118-4:2014/AMD1:2017 – 9 –
IEC 2017
To determine whether the amplifier is overloaded, apply one of the following tests:
• observe the 'clip indicator' on the amplifier, if one is provided;
• compare the measured output voltage with the manufacturer's specified value, provided
that this is specified as ‘compliance voltage’ according to IEC 62489-1;
• examine the output voltage waveform with an oscilloscope for signs of clipping. This may
be alternatively detected as a sharp increase in THD as the input frequency is increased
to the test frequency.
NOTE 3 The voltage waveform is appropriate to be examined, because if the loop has high inductance, clipping
might not be apparent on the current waveform. When measuring the voltage, note that neither side of the amplifier
output is likely to be at earth potential. For some portable measuring systems, an attenuator might be required to
measure or display the voltage.
Once the test is complete, remove the test signal and adjust the level back to the previous
0 dB level as established in Clause 8.
10.3.3 Requirements
No clipping shall be experienced at the applicable test frequency specified in Table 4 and
level specified in 10.3.2.
10.4 Magnetic noise level due t
...

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