IEC 60118-13:2019

IEC 60118-13 ®
Edition 5.0 2019-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electroacoustics – Hearing aids –
Part 13: Requirements and methods of measurement for electromagnetic
immunity to mobile digital wireless devices

Électroacoustique – Appareils de correction auditive–
Partie 13: Exigences et méthodes de mesure de l'immunité électromagnétique
aux appareils numériques mobiles sans fil

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IEC 60118-13 ®
Edition 5.0 2019-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electroacoustics – Hearing aids –

Part 13: Requirements and methods of measurement for electromagnetic

immunity to mobile digital wireless devices

Électroacoustique – Appareils de correction auditive–

Partie 13: Exigences et méthodes de mesure de l'immunité électromagnétique

aux appareils numériques mobiles sans fil

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.140.50; 33.100.20 ISBN 978-2-8322-7330-2

– 2 – IEC 60118-13:2019 © IEC 2019
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Operation and function of the hearing aid . 8
5 Requirements for electromagnetic immunity. 8
5.1 General . 8
5.2 Compliance criteria . 9
6 Test procedures for immunity to radiated RF electromagnetic fields . 11
6.1 General . 11
6.2 Test setup . 11
6.3 Hearing aid test setting . 11
6.4 Determination of gain . 12
6.5 Measurement of the input related ambient noise (IRAN) . 12
6.6 Hearing aid output coupling during immunity test . 13
6.7 Position of the hearing aid during immunity test . 13
6.8 Measurement of the output related interference level (ORIL) . 14
6.9 Calculation of the input related interference level (IRIL) . 15
6.10 Report. 15
7 Measurement uncertainty for immunity to radiated RF electromagnetic fields . 16
Annex A (informative) Background for establishing test methods, performance criteria
and test levels . 17
A.1 General . 17
A.2 Radiated RF electromagnetic fields – History of the test method . 17
A.3 Performance criteria . 19
A.4 Test field strengths – Bystander compatibility . 19
A.5 Test field strengths – User compatibility . 20
Bibliography . 21

Figure 1 – Example of a test arrangement for hearing aid immunity measurements
using a GTEM cell . 11
Figure 2 – Examples of input-output response curves at 1 kHz and the determination
of gain at an input SPL of 55 dB . 12
Figure 3 – Hearing aid test positions for BTE (upper) and ITE (lower) . 14
Figure A.1 – Ratio of 1:2 between field strength and interference level in dB . 18
Figure A.2 – Example of test arrangement for hearing aid immunity measurements
using dipole antenna . 20

Table 1 – Field strengths of RF test signals to be used to establish immunity for
bystander compatible and user compatible hearing aids . 10

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTROACOUSTICS –
HEARING AIDS –
Part 13: Requirements and methods of measurement
for electromagnetic immunity to mobile digital wireless devices

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60118-13 has been prepared by IEC technical committee 29:
Electroacoustics.
This fifth edition cancels and replaces the fourth edition published in 2016 and constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) it introduces a new measurement method and set of EMC requirements for hearing aids
immunity to mobile digital wireless devices;
b) generic EMC requirements for hearing aids are no longer included – should be covered by
other standards as appropriate.

– 4 – IEC 60118-13:2019 © IEC 2019
The text of this International Standard is based on the following documents:
FDIS Report on voting
29/1024/FDIS 29/1031/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in 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 document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
INTRODUCTION
This part of IEC 60118 specifies methods of measurement and requirements for hearing aid
immunity to digital wireless devices. Most hearing aids contain digital signal processors and
some can contain wireless transceivers.
Experience in connection with the use of hearing aids in recent times has identified digital
wireless devices, such as wireless telephones and GSM mobile phones, as potential sources
of disturbance for hearing aids. Interference in hearing aids depends on the emitted power
from the digital wireless device as well as the immunity of the hearing aid. The performance
criteria in this document will not totally ensure hearing aid users' interference- and noise-free
use of wireless telephones, but will establish useable conditions in most situations.
In practice, a hearing aid user, when using a wireless telephone, will seek, if possible, to find
a position on the ear, which gives minimum or no interference in the hearing aid. Various test
methods have been considered for determining the immunity of hearing aids. When a digital
wireless device is used close to a hearing aid, there is an RF near-field illumination of the
hearing aid. However, validation investigations in preparing this document have shown that it
is possible to establish a correlation between the measured far-field immunity level and the
immunity level experienced by an actual hearing aid used in conjunction with a digital wireless
device. The use of a far-field test has shown high reproducibility and is considered sufficient
to verify and express the immunity of hearing aids. Near-field illumination of the hearing aid
(i.e. by generating an RF field using a dipole antenna) could however provide valuable
information during the design and development of hearing aids.
It is recognized that the new wireless products introduced have to coexist with existing
spectra, potential networks and other wireless products (medical as well as non-medical).
This revision does not address the issue of coexistence, and the user of this document shall
consult applicable entities for guidance.
In this fifth edition of IEC 60118-13, the field strengths and hearing aid positioning during
measurements have been updated for consistency with IEEE C63.19 [1] and
ANSI C63.19 [2]. The field strength levels used since the first edition of IEC 60118-13 was
published in 1997 have demonstrated, through measurements of more than 1 000 hearing aid
models (ref. European Hearing Instrument Manufacturers Association – EHIMA), to be
sufficiently high to ensure well-functioning hearing aids in everyday use, with only a small
expectation of a few complaints regarding interference from digital wireless devices.
Hearing aids where the outputs are non-acoustic, for example bone conduction hearing aids,
are not directly included in this document, but this document can be used if precise
descriptions of measurement setups for these types of hearing aids are given by the
manufacturer.
___________
Numbers in square brackets refer to the Bibliography

– 6 – IEC 60118-13:2019 © IEC 2019
ELECTROACOUSTICS –
HEARING AIDS –
Part 13: Requirements and methods of measurement
for electromagnetic immunity to mobile digital wireless devices

1 Scope
This part of IEC 60118 covers the relevant EMC phenomena for hearing aids. Hearing aid
immunity to high frequency fields originating from digital wireless devices such as mobile
phones was identified as one of the most relevant EMC phenomena impacting hearing aids.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements 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.
IEC 60118-0:2015, Electroacoustics – Hearing aids – Part 0: Measurement of the
performance characteristics of hearing aids
IEC 60318-5, Electroacoustics – Simulators of human head and ear – Part 5: 2 cm coupler
for the measurement of hearing aids and earphones coupled to the ear by means of ear
inserts
IEC 61000-4-3, Electromagnetic compatibility (EMC) – Part 4-3: Testing and measurement
techniques – Radiated, radio-frequency, electromagnetic field immunity test
IEC 61000-4-20, Electromagnetic compatibility (EMC) – Part 4-20: Testing and measurement
techniques – Emission and immunity testing in transverse electromagnetic (TEM) waveguides
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
hearing aid
wearable instrument intended to aid a person with impaired hearing, usually consisting of a
microphone, amplifier, signal processor and earphone, powered by a low-voltage battery, and
possibly also containing an induction pick-up coil and which is fitted using audiometric and
prescriptive methods
Note 1 to entry: Hearing aids can be placed on the body (BW), behind the ear (BTE), in the ear (ITE) or in the
canal (ITC).
3.2
bystander compatibility
immunity of a hearing aid that ensures it is usable in environments where digital wireless
devices are in operation in the proximity of the hearing aid wearer
3.3
user compatibility
immunity of a hearing aid that ensures that it is usable when the wearer is using a digital
wireless device at the wearer's own aided ear
3.4
gain
G
difference between the acoustic or the magnetic equivalent input level (L ) and the
p,in
respective acoustic output level (L )
p,out
Note 1 to entry: The gain is determined at an acoustic input sound pressure level (SPL) of 55 dB or (for induction
pick-up coils) at a magnetic field strength level re 1 A/m of −35 dB which is the magnetic equivalent of 55 dB
(SPL).
Note 2 to entry: G = L – L .
p,out p,in
Note 3 to entry: If not stated otherwise in this document, gain is determined at a frequency of 1 kHz.
3.5
output related interference level
ORIL
sound pressure level at the output of the hearing aid during exposure to a 1 kHz 80 %
amplitude modulated RF signal with time weighting FAST
Note 1 to entry: ORIL = L at 1 kHz, 80 % AM RF.
p, out
Note 2 to entry: This note applies to the French language only.
3.6
input related interference level
IRIL
ORIL with gain (G) subtracted:
IRIL = ORIL − G
Note 1 to entry: IRIL is used to characterize the immunity of a hearing aid.
Note 2 to entry: This note applies to the French language only.
3.7
input related ambient noise
IRAN
equivalent acoustic input sound pressure level that would lead to the acoustic noise output
produced by a hearing aid:
IRAN = ORIL − G
RF off
and
ORIL = L , RF switched off
RF off p, out
Note 1 to entry: IRAN is determined in the same way as IRIL but with the RF signal switched off.
Note 2 to entry: This note applies to the French language only.

– 8 – IEC 60118-13:2019 © IEC 2019
3.8
GSM
global system for mobile communication
Note 1 to entry: This note applies to the French language only.
3.9
TEM cell
closed measuring device in which a voltage difference creates a TEM-mode electromagnetic
field
3.10
GTEM cell
TEM cell that has been altered to extend the usable frequency range
3.11
radio frequency
RF
frequency of electromagnetic radiation within the range of 30 kHz to 30 GHz
Note 1 to entry: This note applies to the French language only.
3.12
microphone mode
hearing aid omnidirectional setting active
3.13
induction pick-up coil mode
hearing aid induction pick-up coil active
3.14
directional mode
hearing aid directional setting active
4 Operation and function of the hearing aid
Hearing aids basically consist of a microphone, an amplifier, an optional induction pick-up coil
and a small earphone (receiver). For behind the ear (BTE) hearing aids, the sound is often fed
to the ear canal by means of an individually made ear mould (ear insert), or with the receiver
in the auditory canal (RITE). In the ear (ITE) and in the canal (ITC) hearing aids, have the
active circuitry located in the ear.
The power source normally used is a small battery. On some hearing aids, the user can
perform some adjustments of the controls of the hearing aid.
5 Requirements for electromagnetic immunity
5.1 General
Clause 5 specifies the electromagnetic immunity requirements for hearing aids to wireless
digital devices. IEC 61000-4-3 describes testing and measurement techniques for general
radiated immunity which shall be applied. For the purpose of the radiated RF electromagnetic
field immunity requirements, two hearing aid user compatibility classes are defined (see 3.2
and 3.3) which are related to the hearing aid user's situation.
A "bystander compatible" hearing aid will ensure that the hearing aid is usable in
environments where digital wireless devices are in operation in the proximity of the hearing
aid wearer.
A "user compatible" hearing aid will ensure that the hearing aid is usable when the hearing
aid wearer is using a mobile digital wireless device at the wearer's own aided ear.
5.2 Compliance criteria
To demonstrate compatibility, the following criteria shall be met when applying the immunity
test levels defined in Table 1 and following the measurement procedure specified in Clause 6:
• the hearing aid operation mode shall not change; and
• the IRIL shall not exceed 55 dB SPL.
Table 1 specifies the field strengths of RF test signals to establish immunity for bystander
compatible and user compatible hearing aids. "Bystander compatibility" criteria shall be
fulfilled as a minimum requirement, whereas "user compatibility" is optional.

– 10 – IEC 60118-13:2019 © IEC 2019

Table 1 – Field strengths of RF test signals to be used to establish immunity
for bystander compatible and user compatible hearing aids
Bystander compatibility User compatibility
IRIL ≤ 55 dB SPL for field strengths, IRIL ≤ 55 dB SPL for field strengths,
E E
V/m V/m
Frequency 0,08 to 0,65 0,65 to 0,96 0,96 to 1,4 1,4 to 2,7 2,7 to 6,0 0,08 to 0,65 0,65 to 0,96 0,96 to 1,4 1,4 to 2,0 2,0 to 2,7 2,7 to 6,0
range in
GHz
Microphone Not relevant 10 Not 10 Not Not relevant 60 Not 40 30 Not
mode relevant relevant relevant relevant
Induction Not relevant 10 Not 10 Not Not relevant 60 Not 40 30 Not
pick-up coil relevant relevant relevant relevant
a
mode
Directional Not relevant 10 Not 10 Not Not relevant Not relevant Not Not Not Not
a
relevant relevant relevant relevant relevant relevant
mode
a
If provided.
6 Test procedures for immunity to radiated RF electromagnetic fields
6.1 General
Clause 6 describes the equipment and measurement methods for the radiated RF
electromagnetic field immunity test. Annex A provides background information for the
development of the procedures.
6.2 Test setup
An example of a suitable test arrangement is given in Figure 1.
Hearing aids whose outputs are non-acoustic, for example, bone conduction hearing aids, will
require use of an appropriate load and coupling device. Precise descriptions of measurement
setups for these types of hearing aids shall be given by the manufacturer.
Proposed testing, validation and measurement techniques, when using a GTEM cell, is to be
found in IEC 61000-4-20.
Figure 1 – Example of a test arrangement for hearing aid
immunity measurements using a GTEM cell
6.3 Hearing aid test setting
The hearing aid gain control shall be adjusted to the reference test setting (RTS), and the
other controls shall be set to the basic settings as described in 6.4.3 in IEC 60118-0:2015
("adaptive features disabled").

– 12 – IEC 60118-13:2019 © IEC 2019
6.4 Determination of gain
For the determination of gain, the same acoustic coupler and tubing as used for the ORIL
measurement shall be used. Measurement setup for determination of gain shall be in
accordance with IEC 60118-0:2015. The gain of a hearing aid in microphone mode is
determined by applying a sinusoidal 1 kHz signal with a sound pressure level (L ) to be
p,in
swept from 30 dB SPL to 80 dB SPL at the microphone reference point of the hearing aid.
From the input-output response curve, take the acoustic sound pressure level of the output
(L ) at 55 dB input level.
p,out
For the gain of a hearing aid in directional mode, use the gain obtained in microphone mode.
The gain of a hearing aid in induction pick-up coil mode is determined by applying a
sinusoidal 1 kHz signal with a magnetic field strength level re 1 A/m (L ) in dB to be swept
H,in
from −60 dB to −10 dB at the induction pick-up coil reference point of the hearing aid,
measuring the acoustic sound pressure level (L ) at its output.
p,out
From this input-output response curve, take the acoustic sound pressure level (L ) input
p,out
level re 1 A/m at −35 dB (which is equivalent to the acoustic sound pressure level of 55 dB);
see examples in Figure 2.
Calculate gain and inductive pick-up coil gain by:
G (dB) = L (dB) – 55 (dB)
p,out
130 120
110 100
Gain =
45 dB
Gain =
100 90
30 dB
50 60 70 80 90
50 60 70 80 90
Input SPL (dB)
Input SPL (dB)
IEC
Figure 2 – Examples of input-output response curves at 1 kHz
and the determination of gain at an input SPL of 55 dB
6.5 Measurement of the input related ambient noise (IRAN)
Perform an ORIL measurement with RF signal switched off to get ORIL .
RF off
Determine IRAN by subtracting gain (G) from ORIL : IRAN = ORIL – G.
RF off RF off
Measurements shall be taken to verify that ambient noise is at least 15 dB below the IRIL limit
of 55 dB SPL.
Output SPL  (dB)
Output SPL  (dB)
6.6 Hearing aid output coupling during immunity test
The hearing aid shall be placed in the RF field.
No objects, other than the hearing aid, which could distort the RF-field, shall be present in the
test volume. In order to remove the metallic coupler as specified in IEC 60318-5 from the test
volume, the normal tubing between the hearing aid and the coupler shall be replaced by
tubing of 2 mm bore and with a length typically between 50 mm and 1 000 mm.
For in the ear hearing aids, the outlet from the receiver shall be coupled to the tubing by a
suitable adapter. This adapter and the length of the tubing are not critical, as the hearing aid
gain is determined in each individual test configuration.
6.7 Position of the hearing aid during immunity test
The hearing aid shall be placed in six measurement orientations, consisting of three
orientations related by 180˚ rotations about a bounding cube ortho-axis, and their three
opposite-side orientations established by 180˚ rotations about the E-field vector from each of
the three original orientations.
The six positions are defined as X0, X180, Y0, Y180, Z0, Z180. The position can be defined
with the following three starting positions X0, Y0, Z0, shown in Figure 3.
Position X180 is attained from the starting position X0 with a rotation 180˚ about the E-field
vector. Position Y180 is attained by starting from the Y0 position and then making a 180˚
rotation about the E-field vector. Position Z180 is attained by starting from the Z0 position and
then making a 180˚ rotation about the E-field vector.
For custom hearing aids, the X0 position is intended to reproduce the normal position of the
device in the ear, with the RF field addressing the side of the head. X180 is attained by
starting at the X0 position and then making a 180˚ rotation about the E-field vector. Y180 is
attained by starting at the Y0 position and then making a 180˚ rotation about the E-field
vector. Z180 is attained by starting at the Z0 position and then making a 180˚ rotation about
the E-field vector.
– 14 – IEC 60118-13:2019 © IEC 2019

Figure 3 – Hearing aid test positions for BTE (upper) and ITE (lower)
6.8 Measurement of the output related interference level (ORIL)
For each position, measure the SPL (ORIL) at the output of the hearing aid:
– place the hearing aid in the given orientation inside the test volume;
– for each RF-frequency f = f x 1,01:
n+1 n
• apply the 1 kHz 80 % amplitude modulated RF signal with the field strength according
to Table 1;
• measure the SPL (ORIL) at the output of the hearing aid using a 1 kHz band-pass filter
with a maximum bandwidth of one-third octave.
Gain changes in the hearing aid may occur due to RF carrier effects. This can be investigated
multiple ways. A few examples are listed below.
Gain change can be investigated by applying increasing field strength levels until hearing aid
interference occurs, and compare the increase in measured interference level to the increase
in field strength, when taking the hearing aid input-output response curves into consideration.

Another way to determine if gain change has occurred is to apply a 1 kHz acoustical or a
magnetic tone, depending on hearing aid mode being tested, and switch the carrier wave of
RF on and off without AM, while monitoring the hearing aid output sound pressure level, at the
frequency and hearing aid orientation that produced the highest ORIL in each frequency band
during test. The difference in hearing aid output sound pressure level, while switching the
carrier wave of RF on and off, represents the gain change.
It is also possible to determine if a gain change has occurred by applying a 1 300 Hz acoustic
bias signal, which sets the hearing aid to a known acoustic output level. With a frequency
analyzer, the hearing aid acoustic output at 1 300 Hz can be measured to reveal gain
changes in the hearing aid.
If gain changes are observed during the measurement, it shall be stated in the test report, and
results should be interpreted with care as the RF carrier effects may have activated the signal
processing in the hearing aid in an unpredictable way.
The hearing aid operating mode shall not change. It is up to each manufacturer to determine
what constitutes a mode change for their device and how to monitor for mode changes. An
example of a mode change may be an unintended changing of memories from a microphone
to an induction pick-up coil mode.
Measurements for user compatibility and bystander compatibility can be carried out as two
separate tests according to Table 1. There is no need to perform a bystander compatibility
test for specific frequencies covered by user compatibility testing if user compatibility is
demonstrated. The measurements shall be carried out in microphone mode, directional mode
(if provided) and induction pick-up coil mode (if provided).
NOTE Positioning the hearing aid in 6 discrete positions has been found to be suitable for hearing aid immunity
testing (see [2]).
6.9 Calculation of the input related interference level (IRIL)
The test result at each frequency is the highest measured ORIL obtained from the different
test orientations. This can be expressed in terms of the individual ORIL measurements by:
ORIL = max(ORIL , ORIL , ORIL , ORIL , ORIL , ORIL )
max X0 X180 Y0 Y180 Z0 Z180
The worst-case calculated ORIL result for each carrier frequency range is converted to IRIL by
IRIL = ORIL – G
max max
Repeat for each input mode; microphone mode, inductive pick-up coil mode (if provided) and
directional mode (if provided).
6.10 Report
The results shall be reported as IRIL values for all input modes and carrier frequency ranges.
For each mode, state pass or fail. To claim pass, the hearing aid operating mode shall not
change and IRIL shall be ≤ 55 dB SPL for all frequencies, field strengths, and test
max
positions listed to meet the requirements of this document.
Test setup, device settings, and IRAN shall be reported.

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7 Measurement uncertainty for immunity to radiated RF electromagnetic fields
The maximum measurement uncertainty for acoustic measurements shall be:
U = ±2 dB
max, Acoustic
NOTE Acoustic U is in accordance with IEC 60118-0:2015.
max
The measurement uncertainty of the method in Clause 6 is composed of several components:
– uncertainty derived from the equipment used, such as generators, level meters, RF
coupler, RF probe placement, etc.;
– reproducibility of positioning the hearing aid.
Considering the components above, the measurement uncertainty in the RF part can be
determined.
U = ±3 dB
max, Radio Frequency
NOTE It is good practice to validate the uncertainty by comparing measurement results with an accredited test
laboratory.
Manufacturers and purchasers may utilize the uncertainty differently. Manufacturers shall
ensure that their production test results fall within prescribed tolerances that are reduced by
the measurement uncertainty.
Purchasers can make their decisions based on the nominal data expanded by the
measurement uncertainty.
Annex A
(informative)
Background for establishing test methods,
performance criteria and test levels
A.1 General
In 1994, the European Hearing Instrument Manufacturers Association (EHIMA) undertook a
series of measurements to establish a basis for measuring the effects of interference on
hearing aids, and for quantifying practical limits of immunity. In Australia, similar work was
undertaken at around the same time. This work concentrated on providing the basis for
measuring and specifying what is now known as the bystander problem. At that time, the
issue of user compatibility and the need to deal with it was limited by the lack of knowledge
on the subject and the low use of digital wireless devices in most countries.
However, the rapid growth in the use of digital wireless devices produced an urgent need to
address the issue of the hearing aid wearer who wanted to use a digital wireless device. Work
on this problem commenced in the USA in 1997 and led to proposals for methods of
measurement for both hearing aids and mobile phones. This work led to ANSI C63.19 [2],
which provided the impetus for further work in Europe to evaluate the proposals.
A.2 Radiated RF electromagnetic fields – History of the test method
The EHIMA GSM project final report [4] presents the results of the development phase of the
EHIMA GSM project, which is a comprehensive project set up by EHIMA to establish a test
environment enabling the GSM interference problems to be addressed by the member
companies. It also includes results from other investigations carried out in connection with the
EHIMA GSM project.
The relevant parts of the project are summarised below.
Five hearing aid types were selected for a laboratory investigation, representing different
electroacoustic characteristics, interference levels and interference spectra. The overall input
related interference level (OIRIL), expressed as SPL in decibels, was chosen to characterise
the interference performance of the hearing aids.
First, the aids were tested acoustically according to IEC 60118-0. To enable the metallic ear
simulator to be removed from the RF-field, coupling between the hearing aid and ear
simulator was modified by using 500 mm long tubing. Relatively large variations in the
acoustical effect of this modification were seen. This means that the hearing aid gain should
be measured for the individual hearing aid under test in the determination of OIRIL.
The hearing aids were then exposed to a simulated GSM RF-field in an RF anechoic room
placed in a position corresponding to normal use. A test signal having a peak field strength of
10 V/m was used. This corresponds to a digital wireless device having a power of 8 W at a
distance of 2 m, or to a 2 W wireless device at a distance of 1 m.
The frequency spectrum of the interference signal at the orientation causing maximum
interference was determined. The input related spectrum was then calculated by subtracting
the hearing aid gain, and finally the OIRIL was determined.
The input related spectra appeared almost identical for all the hearing aids tested, the level of
the harmonics decreasing with the increasing frequency. This means that only the low
frequency part of the spectrum is needed to determine OIRIL with sufficient accuracy for the
purpose of measuring immunity.

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It was seen that rotation of the hearing aid in the horizontal plane affected the interference
performance to some degree and that maximum interference occurs at different angles for
different hearing aids. In practically all cases, vertical E-polarisation of the RF-field, as used
in the GSM system, gave rise to the highest interference levels.
Relatively large differences in OIRIL between different hearing aid types were seen, and also
in a small number of cases between samples of the same type.
A ratio of 1:2 between field strength and interference level, expressed in dB, was seen for a
field strength range where the interference signal is above the noise floor of the (linear)
hearing aid and does not saturate it (Figure A.1).

Figure A.1 – Ratio of 1:2 between field strength and interference level in dB
Experiments were carried out to determine the effect of placing the hearing aid behind the ear
and in the ear. It turned out that the human head significantly attenuated the GSM signal
when the head was between the transmitting source and the hearing aid, whereas no
significant difference was seen when the hearing aid was facing the transmitting source.
Based on these findings, it was therefore decided that no "human-factor" correction to the
measuring results was required.
The investigations also showed that the use of 80 %, 1 kHz sine modulation with the same
"peak RMS" level of the carrier as the simulated GSM signal produced approximately the
same input related interference level in the hearing aid. This is in agreement with the
conclusions and recommendations of IEC 61000-4-3. It was therefore decided to recommend
sine modulation for testing of hearing aids. The measurement result is denoted IRIL (input
related interference level). It is determined in the same way as OIRIL, but only the frequency
component at 1 kHz is considered.
In the period 2015 to 2017, radiated RF electromagnetic field measurement methods were
further investigated according the 6-orientations-maximal-sum-method and field strengths
were determined to get about the same IRIL values as with the previously used HA rotation
method; see [5] and [2].
A.3 Performance criteria
To establish a basis for proposing acceptance levels, a series of listening tests were carried
out. As the input related spectrum of the interference signal was almost identical for all the
hearing aids, only one of the signals was presented to a group of five people of normal
hearing instructing them to judge the interference as "not annoying", "slightly annoying",
"annoying" and "very annoying". The interference signals were presented at different levels
together with three different noise and speech signals to simulate different listening situations.
From the results of these tests, acceptance levels expressed as free field SPLs, are
proposed.
Based on the results of these listening tests and the laboratory
...