IEC 60118-13:2011

IEC 60118-13 ®
Edition 3.0 2011-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electroacoustics – Hearing aids –
Part 13: Electromagnetic compatibility (EMC)

Électroacoustique – Appareils de correction auditive –
Partie 13: Compatibilité électromagnétique (CEM)

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IEC 60118-13 ®
Edition 3.0 2011-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electroacoustics – Hearing aids –
Part 13: Electromagnetic compatibility (EMC)

Électroacoustique – Appareils de correction auditive –
Partie 13: Compatibilité électromagnétique (CEM)

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX S
ICS 17.140.50; 33.100.20 ISBN 978-2-88912-456-5

– 2 – 60118-13  IEC:2011
CONTENTS
FOREWORD . 3

INTRODUCTION . 5

1 Scope . 7

2 Normative references . 7

3 Terms and definitions . 8

4 Requirements for immunity . 9

5 Immunity test procedures . 10

6 Measurement uncertainty . 13
Annex A (informative) Background for establishing test methods, performance criteria
and test levels . 15
Bibliography . 20

Figure 1 – Example of a test arrangement for hearing aid immunity measurements
using a one-port TEM cell (asymmetric septum) . 11
Figure 2 – Examples of input-output response curves at 1 000 Hz and the
determination of gain at an input level of 55 dB . 12
Figure 3 – Positioning of hearing aid during RF exposure . 12
Figure 4 – Examples of determination of IRIL by electromagnetic immunity (EMI)
testing . 13
Figure A.1 – Ratio of 1:2 between field strength and interference level in dB . 16
Figure A.2 – Example of test arrangement for hearing aid immunity measurements
using dipole antenna . 18
Figure A.3 – Digital wireless devices antenna designs . 19

Table 1 – Field strengths of RF test signals to be used to establish immunity for
bystander compatible and user compatible hearing aids . 9

60118-13  IEC:2011 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
ELECTROACOUSTICS –
HEARING AIDS –
Part 13: Electromagnetic compatibility (EMC)

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
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. It has the status of a product EMC standard in accordance with
IEC Guide 107, Electromagnetic compatibility – Guide to the drafting of electromagnetic
compatibility publications.
This third edition cancels and replaces the second edition published in 2004 and constitutes a
technical revision. It introduces a new set of requirements for use of hearing aids with mobile
phones.
– 4 – 60118-13  IEC:2011
The text of this standard is based on the following documents:

FDIS Report on voting
29/737/FDIS 29/745/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 publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts of the IEC 60118 series, under the general title: Electroacoustics – Hearing
aids, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site 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.
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.
60118-13  IEC:2011 – 5 –
INTRODUCTION
This standard introduces specifications for EMC requirements for hearing aids.

Hearing aids basically consist of a microphone, an amplifier, a 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). In the ear (ITE) hearing

aids have the active circuitry located in the auditory canal.

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, which in some cases is by

means of a remote control.
The standard only deals with hearing aid immunity, as experience has shown that hearing
aids do not emit electromagnetic signals to an extent that can disturb other equipment. Other
EMC phenomena, such as RF emission and electrostatic discharge, are not currently known
to be a significant problem in connection with hearing aids. Based on new knowledge, they
could be considered in connection with future revisions or extensions of this standard.
Hearing aids containing RF transmitting equipment are covered by this standard regarding
immunity, however the RF transmitting equipment is not covered. Experience in connection
with the use of hearing aids in recent times has identified digital wireless devices, such as
DECT wireless phones and GSM mobile phones as potential sources of disturbance for
hearing aids. Interference in hearing aids depends on the emitted power from the wireless
telephone as well as the immunity of the hearing aid. The performance criteria in this standard
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 digital wireless device, will seek, if possible, to find a position on the ear
which gives a minimum or no interference in the hearing aid.
Hearing aids are battery powered devices, and therefore disturbances related to a.c. or d.c.
power inputs are not relevant and are therefore not considered in this standard.
Hearing aids whose outputs are non-acoustic, e.g. cochlear implants and bone conduction
hearing aids, are not covered by this standard.
In some cases, hearing aids are connected to other equipment by cable, but this standard
does not cover common mode transients and common mode surges on such cable
connections.
Based on experience in connection with the use of hearing aids, relevant sources of
disturbance for hearing aids include low frequency radiated magnetic fields, which may

interact with the induction pick-up coil input included in some hearing aids. As the induction
pick-up coil input is an intended feature of some hearing aids, and the hearing aid therefore
must have a certain sensitivity to low frequency magnetic fields, it is not relevant to specify
immunity against disturbing low frequency magnetic fields. To avoid unintended interference
from low frequency magnetic noise fields, the recommendations specified in IEC 60118-4 [1] ,
regarding specifications for induction loop systems, should be followed.
With regard to high frequency radiated electromagnetic fields originating from RF wireless
devices such as digital mobile telephone systems, only sources of disturbance which are
currently known to be a problem in connection with hearing aids are covered. Reference is
made to IEC 61000-4-3, which identifies digital radio telephone systems operating in the
frequency ranges 0,8 GHz to 0,96 GHz and 1,4 GHz to 2,48 GHz to be potential sources of
interference. Future versions may add tests for other frequency bands, as they come into
more common use. Hearing aids are used in all environments as outlined in IEC 61000-4-3.
___________
Figures in square brackets refer to the bibliography.

– 6 – 60118-13  IEC:2011
Various test methods have been considered for determining the immunity of hearing aids.

When a wireless telephone is used close to a hearing aid, there is an RF near-field

illumination of the hearing aid. However, validation investigations in preparing this standard

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 bring valuable information during design and development of hearing

aids.
60118-13  IEC:2011 – 7 –
ELECTROACOUSTICS –
HEARING AIDS –
Part 13: Electromagnetic compatibility (EMC)

1 Scope
This part of IEC 60118 in principle covers all relevant EMC phenomena for hearing aids. EMC
phenomena, such as RF emission and electrostatic discharge, are not currently known to be a
significant problem in connection with hearing aids and are therefore not dealt with. Based on
new knowledge, they could be considered in connection with future revisions or extensions of
this standard. Hearing aid immunity to high frequency electromagnetic fields originating from
digital wireless devices operating in the frequency ranges 0,8 GHz to 0,96 GHz and 1,4 GHz
to 2,48 GHz is currently identified as the only relevant EMC phenomenon regarding hearing
aids. Future editions of this part of IEC 60118 may add tests for other frequency bands, as
they come into more common use. IEC 61000-4-3 is the basis for relevant EMC tests to be
conducted on hearing aids. Measurement methods and acceptance levels are described in
this part of IEC 60118.
For the purpose of this part of IEC 60118, two immunity classes of hearing aids are defined
(see 3.1) related to their use. "Bystander compatible" ensures that a hearing aid is usable in
environments where digital wireless devices are in operation in the proximity of the hearing
aid wearer. "User compatible" hearing aids ensures that a hearing aid is usable when the
wearer is using a digital wireless device at the wearer’s own aided ear.
Measurement methods for hearing aids with non-acoustic outputs and for hearing aids
connected to other equipment by cables are not given in this standard.
2 Normative references
The following referenced documents are indispensable for the application 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, Hearing aids – Part 0: Measurement of electroacoustical characteristics
IEC 60118-2, Hearing aids – Part 2: Hearing aids with automatic gain control circuits

IEC 60118-7, Electroacoustics – Hearing aids – Part 7: Measurement of the performance
characteristics of hearing aids for production, supply and delivery quality assurance purposes
IEC 60318-4, Electroacoustics – Simulators of human head and ear – Part 4: Occluded-ear
simulator for the measurement of earphones coupled to the ear by means of ear inserts
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

– 8 – 60118-13  IEC:2011
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60118-0,

IEC 60118-7, and IEC 61000-4-3 as well as the following apply.

3.1
hearing aid
wearable instrument, containing a variety of individual adjustment facilities, intended to aid a

person with impaired hearing. Consisting of a microphone, amplifier, an induction pick-up coil

(optional) and earphone, powered by a battery

NOTE Hearing aids can be placed on the body (BW), behind the ear (BTE) or in the ear (ITE).
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 (2 m, see A.4)
3.3
user compatibility
immunity of a hearing aid that ensures it is usable when the wearer is using a digital wireless
device at the wearer´s own aided ear
3.4
reference orientation (of a hearing aid)
orientation of the hearing aid with respect to the RF emitting source which corresponds to the
orientation of the hearing aid under actual use on a person facing or using an RF emitting
source
3.5
input related interference level
IRIL
level used to characterise the immunity of the hearing aid
NOTE Acoustic IRIL is expressed relative to 20 µPa in decibels, and is calculated by subtracting the gain of the
hearing aid from the level of a 1 kHz signal measured at the output of the hearing aid during exposure to a 1 kHz
modulated RF field in microphone mode. The gain of the hearing aid is determined at 1 kHz using an input sound
pressure level of 55 dB.
If the hearing aid provides an additional directional microphone, the gain determined with the omnidirectional
microphone is used for determination of IRIL.
If the hearing aid provides an induction pick-up coil, the control settings used for acoustic measurement are used.
Induction pick-up coil IRIL is expressed as the equivalent acoustic input r.m.s levels re 20 µPa in decibels, based

on the assumption that the magnetic field strength level re 1A/m of –20 dB is practically equivalent to the acoustic
sound pressure level of 70 dB.
2)
The induction pick-up coil IRIL is calculated by subtracting the output of the hearing aid in dB minus 55 dB, from
the level of 1 kHz signal measured at the output of the hearing aid during exposure to a 1 kHz 80% modulated RF
field in induction pick-up coil mode.
Decreasing values of IRIL indicate increasing immunity.
Further details are given in Annex A.
3.6
GSM
global system for mobile communication
___________
Determined at –35 dB input level re 1A/m at 1 kHz.

60118-13  IEC:2011 – 9 –
3.7
TEM cell
closed measuring device in which a voltage difference creates a TEM-mode electromagnetic

field
3.8
radio frequency
RF
frequency of electromagnetic radiation within the range of 30 kHz to 30 GHz

4 Requirements for immunity
Table 1 states the field strengths of RF test signals to establish immunity for bystander
compatible and user compatible hearing aids. Bystander compatibility shall be fulfilled as a
minimum specification, whereas user compatibility is an additional feature, which can be
claimed if the specifications are met by the hearing aid.
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 for field strengths, IRIL ≤ 55 dB for field strengths,
E in V/m E in V/m
Frequency <0,8 0,8- 0,96-1,4 1,4- 2,0- >2,48 <0,8 0,8-0,96 0,96-1,4 1,4-2,0 2,0-2,48 >2,48
range GHz 0,96 2,0 2,48
Microphone Unneces 3,5 Unneces 2 1,5 Unneces Unneces 90 Unneces 50 35 Unnece
mode sary sary sary sary sary ssary
Induction Unneces 3,5 Unneces 2 1,5 Unneces Unneces 90 Unneces 50 35 Unnece
pick-up coil sary sary sary sary sary ssary
a
mode
Directional Unneces 3,5 Unneces 2 1,5 Unneces Unneces Unneces Unneces Unneces Unneces Unnece
microphone sary sary sary sary sary sary sary sary ssary
a
mode
Test field strengths are given as unmodulated carrier levels.
a
If provided by the hearing aid.

NOTE 1 Table 1 has been updated for frequencies above 2,0 GHz. Wireless services like Bluetooth operate in the
2,0 GHz to 2,48 GHz range. Services in this frequency range are typically running at lower power levels compared
to services below 1 GHz. TDMA modulation (eg. used in GSM mobile phones and DECT wireless phones) has been
shown to generate the most aggressive interference in hearing aids to date, while CDMA and other modulations
schemes are less aggressive. The test levels used since the first edition of IEC 60118-13 in 1996 have through
testing of more than 1 000 hearing aid models demonstrated to be sufficiently high to ensure well-functioning

hearing aids in daily life, with only a few complaints from hearing aid users who are annoyed by interference from
digital wireless devices. A test field strength 3 dB below the 1,4 GHz to 2,0 GHz range is considered sufficient to
sustain well-functioning hearing aids in daily life regarding interference in the 2,0 GHz to 2,48 GHz range because
services in the latter frequency range are typically running at lower power levels compared to services below
1 GHz. Additional national standards may supplement ranges in Table 1.
NOTE 2 As sources of disturbance in the frequency range 0,96 GHz to 1,4 GHz, below 0,8 GHz and beyond
2,48 GHz are not known to affect hearing aids, testing in this frequency range is not considered necessary. If the
hearing aid provides an additional microphone input option – directional microphone intended for distant listening
in noisy environments – user compatibility is not considered relevant in this position. Compatibility in induction
pick-up coil mode is considered important to establish interference free conditions in induction loop environments,
and to ensure the ability to use the induction pick-up coil as an input transducer for assistive listening devices for
digital wireless devices, e.g. portable hands free kits.
NOTE 3 The requirements to generate high field strengths might drive the RF power amplifier to generate
distortion. Care should be taken to ensure that distortion does not affect the measurement results.

– 10 – 60118-13  IEC:2011
5 Immunity test procedures
5.1 A typical RF-test equipment, test configuration and test procedures, e.g. as specified in

IEC 61000-4-20 shall apply. This requires that a 1 kHz 80% sine modulation of the carrier

wave is used. As described in A.2, this is a suitable signal for immunity test of hearing aids.

NOTE For small systems without wires (such as hearing aids) suitable GTEM cells and striplines may be used as

indicated in IEC 61000-4-20.
5.2 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 ear simulator or coupler as specified in IEC 60318-4 and
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 between 50 mm and 1 000 mm.
The choice of ear simulator or coupler and the length of the tubing are not critical, but
identical setup should be used for measurement of hearing aid gain and IRIL. For in-the-ear
instruments, 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. An example of a suitable test arrangement is given in
Figure 1.
60118-13  IEC:2011 – 11 –
l
a
b
c
e
d   m
f g o
n
h i p
q
j
k
IEC  694/11
NOTE Measurements should be made to ensure that the background noise level of the test configuration is at
least 10 dB lower than the lowest measured acoustic output from the hearing aid.
Key
a hearing aid
b directional coupler
c TEM cell
d RF signal
e RF signal
f power amplifier
g power sensor
h RF generator
i power meter
j measurement instrument interface
k measuring programme
l 500 mm Ø2 mm tubing
m coupler or ear simulator
n audio signal
o microphone power supply
p BP filter, 1 kHz, one-third-octave
q multimeter
Figure 1 – Example of a test arrangement for hearing aid immunity measurements
using a one-port TEM cell (asymmetric septum)
5.3 The hearing aid gain control shall be adjusted to the reference test setting and the other
controls shall be set to the basic settings as described in IEC 60118-7.
5.4 With the acoustical coupling described in 5.2 and the test conditions described in 5.3,
the input-output response of the hearing aid shall be measured at 1 000 Hz as described in
IEC 60118-2. This test applies for all hearing aids. From the input-output response curve,
determine the gain obtained at 55 dB SPL input level. If the hearing aid provides an induction

– 12 – 60118-13  IEC:2011
pick-up coil, determine the output sound pressure level for an input level re 1 A/m of -35 dB.

Examples of input-output response curves are given in Figure 2.

120 110
110 100
Gain = 45 dB
100 90
Gain = 30 dB
55 55
50 60 70 80 90 50 60 70 80 90
Input SPL  (dB) Input SPL  (dB)
IEC  695/11
Figure 2 – Examples of input-output response curves at 1 000 Hz
and the determination of gain at an input level of 55 dB
5.5 The hearing aid, with the controls set as in 5.3, shall be placed in the RF field, and the
sound pressure level of the hearing aid at 1 000 Hz shall be determined with the use of a
band-pass filter with a maximum bandwidth of one-third octave.
The hearing aid shall be placed in the reference orientation (see Figure 3 and 3.4) and then
rotated in steps of 90° in the horizontal plane. For each orientation the carrier frequency shall
be stepped or swept as specified in IEC 61000-4-3, using a step size of 1% of the carrier
frequency.
E E
Field propagation
direction
0°
H H
Rotation Rotation
direction direction
0°
Field
propagation
direction
IEC  696/11
Figure 3 – Positioning of hearing aid during RF exposure
Gain changes in the hearing aid may occur due to RF carrier effects. This phenomenon can
be investigated by applying increasing field strength levels and monitor the acoustic output of
the hearing aid for saturation effects, or by applying a 1 300 Hz acoustic bias signal to the
microphone input tube, 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
Output SPL  (dB)
Output SPL  (dB)
60118-13  IEC:2011 – 13 –
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 and unpredictable way.

NOTE Rotation of the hearing aid in four discrete positions corresponding to the hearing aid placement under

actual use is found to be suitable for hearing aid immunity testing (see Annex A).

5.6 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 if user compatibility is demonstrated. The measurements shall be carried out

with the microphone, directional microphone (if provided) and induction pick-up coil (if

provided). For directional microphones, the output value measured in 5.4 with the

omnidirectional microphone is used for determination of IRIL. For a induction pick-up coil, the

output value measured in 5.4 with an input level re 1 A/m of –35 dB is used for determination
of IRIL. Figure 4 gives examples of determination of IRIL.
EMI test field strength 90 V/m EMI test field strength 50 V/m
Orientations (°): 0°, 90°, 180°, 270° Orientations (°): 0°, 90°, 180°, 270°
70 70
0° 0°
90° 90°
65 65
180° 180°
60 60
270° 270°
55 dB IRIL 55 dB IRIL
55 55
50 50
45 45
40 40
Not user User compatible Not user
User compatible
compatible compatible
35 35
30 30
800 850 900 950 1 400 1 700 2 000 2 300 2 480
Carrier frequency  (MHz) Carrier frequency  (MHz)

IEC  697/11
Figure 4 – Examples of determination of IRIL by electromagnetic immunity (EMI) testing
5.7 The results shall be reported as IRIL values for all input options and carrier frequency

ranges e.g. if IRIL ≤ 55 dB SPL for a field strength of 90 V/m in the frequency range 800 MHz
to 960 MHz, in microphone mode, the result shall be reported as follows: user compatible
800 MHz to 960 MHz, microphone mode.
User compatibility can be reported for frequency ranges more narrow than the complete test
range, e.g. user compatible 1 714 MHz to 1 856 MHz. Consequently user compatibility to up-
link frequencies in certain digital wireless devices networks, for example, can be claimed even

if the hearing aid is not user compatible in the complete test range.
6 Measurement uncertainty
The measurement uncertainty is composed of several components:
– uncertainty derived from the equipment used, such as generators, level meters, measuring
microphones, coupler etc.;
– variance in the acoustic coupling of the hearing aid to the coupler, for example relating to
diameter and length of tubing;
– reproducibility of positioning the hearing aid.
Considering the above components the measurement uncertainty can be determined.
NOTE It is good practice to validate the uncertainty by comparing measurement results with an accredited test
laboratory.
Interface level IRIL  (dB)
Interface level IRIL  (dB)
– 14 – 60118-13  IEC:2011
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.
Purchaser may make their decisions based in the nominal data expanded by the

measurement uncertainty.
60118-13  IEC:2011 – 15 –
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 a practical limit 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 compatibility. 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 the ANSI C63.19 [4]
standard, which provided the impetus for further work in Europe to evaluate the proposals.
A.2 Test methods
The EHIMA GSM project was set up to establish a test environment enabling the GSM
interference problems to be addressed. The project’s final report [2] presents the results of
the development phase. It also includes results from other investigations. 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 a 2 W 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 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.
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

– 16 – 60118-13  IEC:2011
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).

−30 −20 −10 0 10 20 30
Field strength, re 10 V/m  (dB)
IEC  698/11
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 %, 1 000 Hz 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 1 000 Hz is considered.
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.
Interference level  (dB)
60118-13  IEC:2011 – 17 –
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 investigation, it is concluded

that an acceptance SPL around 55 dB will probably ensure acceptable conditions for the

hearing aid user in most practical situations. This value has been chosen as the performance

criterion in this standard. The choice was confirmed by an additional investigation using

hearing impaired subjects.
To summarise, IRIL – the input related interference level at 1 000 Hz measured as a sound

pressure level in decibels – should be used to characterise the immunity of the hearing aid.

Decreasing values of IRIL indicate increasing immunity. The acceptance level corresponding
to IRIL equal to or less than 55 dB SPL will probably ensure acceptable conditions for the
hearing aid user in most practical situations and is recommended as the performance
criterion.
A.4 Test field strengths – Bystander compatibility
To be able to suggest realistic field strengths for testing hearing aids, i.e. field strengths
which simulate situations where the hearing aid user is disturbed by a nearby person using a
digital wireless device, a number of points should be taken into account.
Firstly, the proposed test procedure is based on a number of worst case considerations:
– The maximum interference level is found in each of four different orientations of the
hearing aid relative to the disturbing field, and out of these four maxima the highest is
used to characterise the interference level in the hearing aid.
– If compliance to the standard is documented, the maximum interference level within a wide
frequency band is used to characterise the immunity of the hearing aid in the frequency
band, even if the maximum interference level is only obtained at a single frequency.
NOTE As the immunity test is performed in a broad frequency band, the frequency with the worst case
interference will seldom coincide with an actual carrier frequency.
– The field strength corresponding to maximum transmitting power is used, despite the fact
that digital wireless devices only transmit with maximum power in certain situations
(battery fully charged, large distance between the digital wireless device and the base
station).
Secondly, another practical circum
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