IEC 60118-9:2019

IEC 60118-9 ®
Edition 2.0 2019-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electroacoustics – Hearing aids –
Part 9: Methods of measurement of the performance characteristics of bone
conduction hearing aids
Électroacoustique – Appareils de correction auditive –
Partie 9: Méthodes de mesure des caractéristiques fonctionnelles des appareils
de correction auditive à conduction osseuse

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IEC 60118-9 ®
Edition 2.0 2019-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electroacoustics – Hearing aids –

Part 9: Methods of measurement of the performance characteristics of bone

conduction hearing aids
Électroacoustique – Appareils de correction auditive –

Partie 9: Méthodes de mesure des caractéristiques fonctionnelles des appareils

de correction auditive à conduction osseuse

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.140.50 ISBN 978-2-8322-7332-6

– 2 – IEC 60118-9:2019 © IEC 2019
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Measurement method . 11
4.1 General . 11
4.2 Mechanical coupler . 11
4.3 Skull simulator . 11
4.4 Measurement frequency range . 11
4.5 Reporting of data . 12
5 Measurement enclosure and measurement equipment. 12
5.1 General . 12
5.2 Unwanted stimuli in the test enclosure . 12
5.3 Sound source . 12
5.4 Measurement system for the measurement of the vibratory force level
produced by a bone conduction hearing aid . 12
5.5 Direct-current measuring system . 13
5.6 Magnetic field source for ETLS and MMSL measurements . 13
6 Measurement conditions . 14
6.1 General . 14
6.2 Applying the bone vibrator to the mechanical coupler or skull simulator . 14
6.2.1 Transcutaneously coupled devices . 14
6.2.2 Bone coupled devices . 14
6.3 Control of the sound field . 15
6.3.6 Battery or supply voltage . 17
6.3.7 Settings of controls . 18
6.4 Ambient conditions. 18
6.4.1 Measurement space . 18
6.4.2 Bone vibrator, mechanical coupler and skull simulator . 18
7 Measurement procedures . 19
7.1 Frequency response curves . 19
7.2 OVFL90 frequency response curve . 19
7.3 Full-on acousto-mechanical sensitivity level frequency response . 20
7.4 Basic vibratory force level frequency response . 21
7.4.1 Measurement procedure . 21
7.4.2 Frequency range . 21
7.5 Total harmonic distortion . 21
7.6 Equivalent input noise . 22
7.7 Battery current . 22
7.8 Measurements for hearing aids having an induction pick-up coil . 22
7.8.1 General . 22
7.8.2 Equivalent test loop sensitivity (ETLS) . 23
7.8.3 Maximum HFA magneto-mechanical sensitivity level (HFA- MMSL) of
induction pick-up coil . 23
8 Maximum permitted expanded uncertainty of measurements . 23

Bibliography . 26

Figure 1 – Example of a bone coupled device (hearing aid with integral bone vibrator)
mounted on a skull simulator . 15
Figure 2 – Example of a transcutaneously coupled device (spectacle hearing aid with

an integral bone vibrator mounted in the spectacle arm) under measurement . 16
Figure 3 – Example of a transcutaneously coupled device (hearing aid with external
bone vibrator) mounted on the mechanical coupler . 17
Figure 4 – Example of OVFL90 curve and basic force level frequency response curve . 20
Figure 5 – Relationship between tolerance limits, corresponding acceptance intervals
and the maximum permitted uncertainty of measurement, U . 24
MAX
Table 1 – Resistors and open circuit voltages for zinc-air battery simulators . 18
Table 2 – Distortion test frequencies and input sound pressure levels . 22
Table 3 – Example uncertainty budget . 25

– 4 – IEC 60118-9:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTROACOUSTICS –
HEARING AIDS –
Part 9: Methods of measurement of the performance
characteristics of bone conduction hearing aids

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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6) All users should ensure that they have the latest edition of this publication.
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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 60118-9 has been prepared by IEC technical committee 29:
Electroacoustics.
This second edition cancels and replaces the first edition published in 1985. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) includes bone coupled devices measured on a skull simulator;
b) measurement frequency range increased to 8 000 Hz for bone coupled devices.

The text of this International Standard is based on the following documents:
FDIS Report on voting
29/1025/FDIS 29/1029/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.
– 6 – IEC 60118-9:2019 © IEC 2019
INTRODUCTION
IEC 60118-0 gives information on methods of measurement for air conduction hearing aids.
The majority of hearing aids in use are of this type, but a small percentage use a bone
vibrator instead of an earphone. The use of a bone vibrator requires a different method of
measuring the output from the hearing aid and also makes it impractical to measure
amplification directly in terms of acoustic gain.
Amplification in the case of an air conduction hearing aid is expressed as the difference
between the output sound pressure level in an acoustic coupler or ear simulator and the
input sound pressure level measured in a specified manner. However, with bone
conduction hearing aids, the input is in terms of sound pressure level, but the output will be
in terms of mechanical vibration measured as a vibratory force or force level.
By means of information provided in this document, the performance of hearing aids with
bone vibrator outputs which do not form an integral part of the hearing aid, for example body-
worn, behind-the-ear hearing aids, or bone conduction implant systems with an external bone
vibrator, can be measured in a similar manner to aids with air conduction outputs as
described in IEC 60118-0.
Where the bone vibrator forms an integral part of the hearing aid, or where it is attached in
some fixed manner to the hearing aid, for example a bone coupled (bone anchored) hearing
aid, its performance cannot be measured in the same way as for body-worn aids, due to the
large dimensions of the mechanical coupler. This document recommends a pressure method
of controlling the input sound pressure level to the hearing aid microphone. As an alternative
to the pressure method, storage of a test enclosure frequency response correction curve can
be used. This method is referred to as the "substitution method".

ELECTROACOUSTICS –
HEARING AIDS –
Part 9: Methods of measurement of the performance
characteristics of bone conduction hearing aids

1 Scope
This part of IEC 60118 specifies methods for the measurement of bone conduction hearing
aid characteristics.
The methods described will produce a suitable basis for the exchange of information or for
direct comparison of the electroacoustical characteristics of bone conduction hearing aids.
These methods are chosen to be practical and reproducible and are based on selected fixed
parameters.
The results obtained by the methods specified in this document express the performance
under the conditions of measurement; however, the performance of the hearing aid under
practical conditions of use will depend upon a number of factors (e.g. effective load
impedance, environmental conditions, acoustical environment, etc.).
This document defines methods of measurement of characteristics of bone conduction
hearing aids both for
• transcutaneously coupled devices measured on a mechanical coupler, meeting the
requirements of IEC 60318-6, and
• bone coupled/bone anchored devices measured on a skull simulator.
NOTE 1 A skull simulator is a mechanical coupler designed to present a specific mechanical impedance to
mechanically coupled vibrator.
NOTE 2 Throughout this document, all sound pressure levels specified are referred to 20 µPa. When
appropriate, sound pressure level will be abbreviated to SPL.
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, Electroacoustics – Hearing aids – Part 0: Measurement of the performance
characteristics of hearing aids
IEC 60318-6, Electroacoustics – Simulators of human head and ear – Part 6: Mechanical
coupler for the measurement on bone vibrators
ISO 3, Preferred numbers – Series of preferred numbers
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

– 8 – IEC 60118-9:2019 © IEC 2019
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
bone conduction hearing aid
wearable instrument intended to aid a person with impaired hearing using an
electromechanical transducer intended to produce the sensation of hearing by vibrating the
cranial bones
Note 1 to entry: A bone conduction hearing aid usually consists of a microphone, amplifier, signal processor, and
bone vibrator, powered by a low-voltage battery, and possibly also containing an induction pick-up coil. It is fitted
using audiometric and prescriptive methods.
Note 2 to entry: The bone vibrator of a hearing aid can be integrated in the same housing with the hearing aid,
can be driven via a cable solution and placed in a separate housing, or can be driven via an inductive link and
implanted in the skull.
Note 3 to entry: Bone conduction hearing aids can be placed on the body (body worn), behind-the-ear (BTE), or
in the mastoid area (ear level).
3.2
transcutaneously coupled hearing aid
bone conduction hearing aid using a device that is coupled by an attractive or a static force to
a human head
3.3
bone coupled hearing aid
device that is implanted or rigidly coupled to the skull bone, via a mechanical coupling or an
abutment to the human head
Note 1 to entry: A bone coupled bone conduction hearing aid is often named a bone-anchored device.
3.4
vibratory force level
VFL
twenty times the logarithm to the base 10 of the ratio of the RMS value of the force
transmitting the vibration to the reference value of 1 µN, expressed in decibels
Note 1 to entry: This note applies to the French language only.
3.5
mechanical coupler
device for measuring the vibratory force level output of a transcutaneously coupled hearing
aid, where the force level is measured by a calibrated mechano-electric transducer coupled to
the source
EXAMPLE As described in IEC 60318-6.
3.6
skull simulator
device for measuring the vibratory force level output of a bone coupled hearing aid, where the
force level is measured by a calibrated mechano-electric transducer coupled to the source
3.7
acousto-mechanical sensitivity
quotient of the vibratory force, produced on a mechanical coupler or a skull simulator by the
bone conduction hearing aid and the sound pressure at the reference point of the hearing aid

3.8
acousto-mechanical sensitivity level
AMSL
twenty times the logarithm to the base 10 of the ratio of the acousto-mechanical sensitivity to
the reference sensitivity of 1 µN/20 µPa, expressed in decibels
Note 1 to entry: To calculate the acousto-mechanical sensitivity level from measurements made in this document,
the following formula can be used:
AMSL = VFL – Input SPL
where
VFL re 1 µN is expressed in decibels.
Note 2 to entry: This note applies to the French language only.
3.9
input sound pressure level
sound pressure level at the hearing aid reference point
3.10
basic vibratory force level frequency response curve
force level frequency response curve obtained with the gain control in the reference test
setting and with an input SPL of 60 dB
3.11
input-output characteristic
plot of the output force level, for a single frequency, measured on a mechanical coupler or a
skull simulator on the ordinate, against the sound pressure level applied to the hearing aid on
the abscissa, with equal decibel scale divisions on each axis
3.12
vertical reference
line through or on a hearing aid which is vertical when the aid is positioned as worn on a head
and a torso simulator
3.13
reference point
point on the bone conduction hearing aid chosen for the purpose of defining its position
3.14
high-frequency average
HFA
average of AMSL or VFL in decibels at 1 000 Hz, 1 600 Hz and 2 500 Hz
Note 1 to entry: This note applies to the French language only.
3.15
gain control
manually or electronically operated control for the adjustment of overall output
3.16
OVFL90
output vibratory force level for 90 dB input SPL
VFL developed on a mechanical coupler or a skull simulator with an input SPL of 90 dB with
the gain control of the hearing aid full-on
Note 1 to entry: It is recognized that the maximum output level may occur with more, or occasionally with less,
input SPL than 90 dB. However, the differences are usually small over the frequency range of interest and the
input SPL of 90 dB makes automatic recording of the OVFL90 curve very convenient.

– 10 – IEC 60118-9:2019 © IEC 2019
3.17
high-frequency average of the OVFL90
high-frequency average of the output vibratory force level for an input sound pressure level of
90 dB
3.18
full-on HFA-AMSL
full-on high-frequency average acousto-mechanical sensitivity level
HFA for an input SPL of 50 dB when the gain control of a bone conduction hearing aid is at its
full-on position
Note 1 to entry: The hearing aid shall be set to maximum possible gain setting. Where possible, the AGC function
of AGC hearing aids shall be set to have minimum effect for all measurements.
Note 2 to entry: The manufacturer shall specify the full-on settings used for measurements by providing either a
test program, a set of programmed settings or by reference to physical control settings.
Note 3 to entry: Other adaptive features, such as some directionality, noise suppression, and feedback
suppression systems etc., which may affect the validity of measurements made with steady-state pure-tone signals,
should be disabled. The settings used for measurements shall be specified by the manufacturer by providing either
a test program, a set of programmed settings or by reference to physical control settings.
3.19
RTS
reference test setting of the gain control
setting of the gain control required to produce, for an input SPL of 60 dB, an HFA-AMSL
within ±1,5 dB of the HFA-OVFL90 minus 77 dB, or, if the full-on HFA gain for an input SPL of
60 dB is less than the HFA-OVFL90 minus 77 dB, the full-on setting of the gain control
Note 1 to entry: For most hearing aids, the use of an input SPL of 60 dB and a 17 dB difference from the OVFL90
helps to ensure that, for an overall speech level of 65 dB SPL, peaks do not exceed the OVFL90.
Note 2 to entry: The manufacturer shall specify the full-on-gain settings used for measurements by providing
either a test program, a set of programmed settings or by reference to physical control settings.
Note 3 to entry: Other adaptive features, such as some directionality, noise suppression, and feedback
suppression systems etc., which may affect the validity of measurements made with steady-state pure-tone signals,
should be disabled. The settings used for measurements shall be specified by the manufacturer by providing either
a test program, a set of programmed settings or by reference to physical control settings.
Note 4 to entry: This note applies to the French language only.
3.20
RTAMSL
reference test acousto-mechanical sensitivity level
HFA-AMSL for an input SPL of 60 dB with the gain control at RTS
Note 1 to entry: This note applies to the French language only.
3.21
AGC
automatic gain control
means (other than peak clipping) by which the gain is automatically controlled as a function of
the level of the signal being amplified
Note 1 to entry: This note applies to the French language only.
3.22
magneto-mechanical sensitivity
quotient of the vibratory force level in newtons (N) produced by the bone conduction hearing
aid on the mechanical coupler or skull simulator and the magnetic field strength in
milliamperes per metre (mA/m) at the test point, at a specified frequency and under
essentially linear input/output conditions

3.23
MMSL
magneto-mechanical sensitivity level
twenty times the logarithm to the base 10 of the ratio of the magneto-mechanical sensitivity to
the reference sensitivity 1 µN/(1 mA/m)
Note 1 to entry: MMSL is expressed in decibels.
Note 2 to entry: This note applies to the French language only.
3.24
VFLIV
VFL in a vertical magnetic field
VFL developed in the mechanical coupler or skull simulator with the gain control at RTS when
the input is −30 dB re 1 A/m (= 31,6 mA/m) sinusoidal alternating magnetic field parallel to the
vertical reference with induction pick-up coil selected
Note 1 to entry: This note applies to the French language only.
3.25
high-frequency average of the VFLIV levels
high frequency average VFL in a vertical magnetic field
4 Measurement method
4.1 General
The preferred acoustic measurement procedure, which shall be applied according to
IEC 60118-0, is based on a method of measurement in which the sound pressure level at the
bone conduction hearing aid reference point is kept constant to simulate free field conditions.
This is accomplished in a test enclosure or acoustic test box by the use of a pressure-
calibrated control microphone, on the assumption that the sound field is homogeneous around
the reference point of the hearing aid.
This method is referred to as "constant entrance sound pressure method" or shortened to
"pressure method" throughout this document.
As an alternative to the pressure method, storage of a test enclosure frequency response
correction curve may be used. This method is referred to as the "substitution method".
4.2 Mechanical coupler
Measurements of the transcutaneously coupled bone conduction hearing aid performance
characteristics are made using a mechanical coupler in accordance with IEC 60318-6.
4.3 Skull simulator
Measurements of the bone coupled hearing aid performance characteristics are made using a
skull simulator which shall be specified by the manufacturer of the bone coupled hearing aid.
4.4 Measurement frequency range
All measurements of the transcutaneously coupled bone conduction hearing aid shall be made
for a stated frequency range of 200 Hz to 5 000 Hz.
All measurements of the bone coupled bone conduction hearing aid shall be made for a stated
frequency range of 200 Hz to 8 000 Hz.

– 12 – IEC 60118-9:2019 © IEC 2019
4.5 Reporting of data
All data reported shall be clearly labelled: "According to IEC 60118-9:2019".
5 Measurement enclosure and measurement equipment
5.1 General
The conditions specified in 5.2 to 5.6 apply. Measurements shall be made at the ISO R40
preferred frequencies (1/40 decade or one-twelfth octave) as specified in ISO 3 unless
otherwise stated.
5.2 Unwanted stimuli in the test enclosure
Unwanted stimuli in the test enclosure, such as ambient noise, mechanical vibrations and
electrical or magnetic stray fields, shall be sufficiently low so as not to affect the test results
by more than 0,5 dB. This can be verified if the output level of the hearing aid falls by at least
10 dB in each frequency analysis band, when the signal source is switched off.
5.3 Sound source
5.3.1 The sound source (pure-tone) shall be capable of producing at the measurement
point the requisite sound pressure levels between 50 dB and 90 dB, with a minimum step size
of 5 dB.
The level of the sound source shall be within ±1,5 dB of the indicated value over the
frequency range from 200 Hz to 3 000 Hz, and within ±2,5 dB of the indicated value over the
range from 3 000 Hz to 8 000 Hz.
If the calibration of the sound source depends on ambient conditions, corrections for such
dependence shall be made when necessary.
5.3.2 The frequency of the sound source shall be within ±2 % of the indicated value. The
frequency interval between data points in frequency response curves shall not exceed one-
twelfth octave or 100 Hz, whichever is greater.
5.3.3 For frequency response and full-on gain measurements, the total harmonic distortion
of the sound source shall not exceed 1 % for a sound pressure level up to and including 70 dB
and 2 % for a sound pressure level greater than 70 dB and up to and including 90 dB.
For harmonic distortion measurements, the total harmonic distortion of the sound source at
the frequencies of the THD measurement shall not exceed 0,5 % up to and including a sound
pressure level of 70 dB and 1 % for a sound pressure level greater than 70 dB and up to and
including 90 dB.
5.4 Measurement system for the measurement of the vibratory force level produced
by a bone conduction hearing aid
The equipment for the measurement of the vibratory force level produced by a bone
conduction hearing aid shall fulfil the following requirements:
a) the vibratory force level measurement system shall be accurate to within ±0,5 dB at the
frequency of calibration;
b) the indication of vibratory force level shall be measured with an expanded uncertainty to
within ±2 dB in the range from 200 Hz to 5 000 Hz and to within ±4 dB in the range from
5 000 Hz to 8 000 Hz;
If, under certain conditions, it is necessary to use a selective measuring system in order to
ensure that the response of the bone conduction hearing aid to the signal can be

differentiated from inherent noise in the bone conduction hearing aid, the use of the selective
system shall be stated in the test report.
5.5 Direct-current measuring system
The direct-current measuring system shall have the following characteristics:
a) an acceptance limit of ±5 % at the value of current measured;
b) direct-current voltage drop across current-measuring device ≤ 50 mV;
c) an impedance not exceeding 1 Ω over the frequency range 200 Hz to 8 000 Hz.
One method of realizing 5.5 c) is to bypass the current meter with an 8 000 µF capacitor. The
capacitor should not shunt the battery or the power supply.
5.6 Magnetic field source for ETLS and MMSL measurements
5.6.1 For the measurement of the equivalent test loop sensitivity (ETLS) and the
magneto-mechanical sensitivity level (MMSL), the magnetic field strength produced by the
magnetic loop is computed from the geometry of the loop.
5.6.2 As the material and the construction of the power source may influence the results,
the actual type of source shall be stated.
NOTE 1 For example, the magnetic field strength in the centre of a square loop with a side of "a" metres and
carrying a current of "i" amperes is given by:
22 i
H = A/m
πa
In the centre of a circular loop with a diameter of "d" metres, carrying a current of "i" amperes, the magnetic field
strength is given by:
i
H = A/m
d
NOTE 2 One way to secure essentially constant current conditions is to drive the magnetic field source from a
device having a constant electromotive force and an internal impedance at least 100 times greater than the
magnetic field source input impedance in the frequency range 200 Hz to 8 000 Hz, which, in the case of a low
impedance generator, can be accomplished by a resistor connected in series with the output of the generator.
5.6.3 The measurement space shall be outside the influence from any field-disturbing iron
or other ferromagnetic material or other material in which eddy currents can be induced that
could give rise to a field disturbance.
5.6.4 The magnetic field source shall be provided with a calibration expressing the
relationship between the magnetic field strength in amperes per metre at the measurement
point and the input current in amperes.
5.6.5 The magnetic field source shall be of such shape and dimensions that inside a
sphere of diameter 10 cm, of which the centre is the measurement point, the deviation from
nominal values in magnitude and direction is less than ± 5 % and ± 10°, respectively.
NOTE A square loop with a side length "a" greater than 0,5 m or a circular loop with a diameter "d" greater than
0,56 m will meet these specifications.
5.6.6 The total harmonic distortion of the magnetic field shall not exceed 1 %.
NOTE This condition will be met if the distortion of the input current is less than 1 %.

– 14 – IEC 60118-9:2019 © IEC 2019
5.6.7 The magnetic field strength at the measurement point shall be maintained within a
acceptance limit of ±20 % over the frequency range 200 Hz to 8 000 Hz.
6 Measurement conditions
6.1 General
Procedures for controlling the sound field and establishing measurement conditions for the
hearing aid are described in 6.2 to 6.4.
6.2 Applying the bone vibrator to the mechanical coupler or skull simulator
6.2.1 Transcutaneously coupled devices
6.2.1.1 Locating the bone vibrator on the mechanical coupler
The centre of the vibrating surface of the bone vibrator shall coincide with the centre of the
mechanical coupler pad. At its centre, the vibrating surface shall be perpendicular to the
axis of the mechanical coupler.
Figure 2 shows an example of a spectacle aid mounted for measurement purposes.
Figure 3 shows an example of a hearing aid with external bone vibrator mounted on the
mechanical coupler.
6.2.1.2 Static force
The bone vibrator shall be applied to the mechanical coupler with a static force of
2,5 N ± 0,3 N. The application of the bone vibrator to the mechanical coupler shall not add
mass to the vibrator. Reference shall be made to IEC 60318-6. The static force may be
measured using a spring balance, care being taken that the force is measured along a line
that coincides with the axis of the mechanical coupler.
The level of static force shall always be higher than or equal to the maximum VFL in order to
ensure proper transfer of stimulation.
6.2.2 Bone coupled devices
6.2.2.1 With mechanical coupling
Attach the device with the mechanical coupling onto the abutment on the skull simulator.
The hearing aid shall be placed with its reference point at the test point in the measurement
space with the vertical reference through the microphone ports aligned with the sound source.
Figure 1 shows an example of an internal bone vibrator in place on the skull simulator (skull
simulator specified by the manufacturer).

Dimensions in millimetres
Key
M measurement space
A sound source
B bone conduction hearing aid
C skull simulator
D control microphone
E reference point
Figure 1 – Example of a bone coupled device
(hearing aid with integral bone vibrator) mounted on a skull simulator
6.2.2.2 Implantable devices
The manufacturer shall specify an implant adaptor that can be replaced with the abutment on
the skull simulator for sufficiently attaching the implant vibrator to the driving axes of the skull
simulator such that the vibrator's movement does not counteract the attachment, and specify
correction data for compensating the difference in reference weight.
The hearing aid shall be placed with its reference point at the test point in the measurement
space with the vertical reference through the microphone ports aligned to the sound source.
6.3 Control of the sound field
6.3.1 The hearing aid reference point is the midpoint of the hearing aid sound inlet port(s).
The input SPL at the hearing aid reference point is kept constant:
a) by means of a control microphone (pressure method – see 6.3.2);
b) with electronic data storage (substitution method – see 6.3.3).
6.3.2 If the pressure method is used, the inlet to the control microphone shall be placed as
close as possible to the hearing aid reference point without touching the hearing aid. For a
15 mm or smaller diameter microphone, the distance from the centre of the diaphragm to the
hearing aid reference point shall be 5 mm ± 3 mm. The axis of the control microphone shall be
orthogonal to the speaker axis and shall intersect it at the hearing aid reference point. A line
through the hearing aid reference point shall coincide with the sound source axis. Figure 1
and Figure 2 show examples of measurement arrangements.
6.3.3 An alternative method of keeping the sound pressure level constant, referred to as
the substitution method, is to position the pressure-calibrated control microphone
5 mm ± 3 mm from the hearing aid reference point and measure the SPL at discrete
frequencies with the model of hearing aid to be tested in its test position. By suitable means,
for instance digital equipment, store and subsequently reproduce the required voltages for
constant SPL at the hearing aid reference point with either the control microphone still in
place or a dummy simulating that microphone in the same place in order to fulfil pressure
method conditions.
– 16 – IEC 60118-9:2019 © IEC 2019
NOTE Methods of test that do not keep the control microphone or a dummy in place can give results that differ
from those obtained using the methods in 6.3.2 and 6.3.3. Different results can also occur if the sound field is
calibrated with a hearing aid other than the model under test in place.
6.3.4 For both methods mentioned in 6.3.2 and 6.3.3, the use of a 15 mm or smaller
microphone is recommended. The diameter of the microphone actually used shall be stated.
6.3.5 Care should be taken that neither the mechanical coupler, skull simulator nor
mechanical support for the hearing aid appreciably disturb the sound field in the vicinity of the
hearing aid at the test frequencies used, and they should not introduce spurious effects
arising from mechanical resonances or mechanical vibrations, nor should they in any respect
affect any mechanical or acoustical property of the hearing aid under test.
Dimensions in millimetres
Key
M measurement space
A sound source
B hearing aid reference point
C control microphone
D rota
...