Electroacoustics - Hearing aids -- Part 7: Measurement of the performance characteristics of hearing aids for production, supply and delivery quality assurance purposes

This part of IEC 60118 gives recommendations for the measurement of the performance characteristics of air-conduction hearing aids of a particular model for production, supply and delivery quality assurance purposes. The manufacturer will normally assign nominal values. This standard does not relate to mechanical or environmental tests. It should not be used as the basis for the exchange of information about hearing aid characteristics in general, nor is it intended to be used as a predictor for real-ear performance. Though the number of measurements covered by this standard is limited, it is not intended that all measurements described herein shall be made in every case. This second edition now specifies performance requirements. Conformance to the specifications in this standard is demonstrated only when the result of a measurement, extended by the actual expanded uncertainty of measurement of the testing laboratory, lies fully within the tolerances specified in this standard extended by the values for Umax given in Table 4. In case of custom-made in-the-ear instruments, the data supplied by the manufacturer applies only to the particular hearing aid being tested.

Akustik - Hörgeräte -- Teil 7: Messung der Übertragungseigenschaften von Hörgeräten zum Zwecke der Qualitätssicherung in der Herstellung, Versorgung und Lieferung

Electroacoustique - Appareils de correction auditive -- Partie 7: Mesure des caractéristiques fonctionnelles des appareils de correction auditive aux fins d'assurance de la qualité de la production, de la livraison et des approvisionnements

Donne des recommandations pour la mesure des caractéristiques fonctionnelles des appareils de correction auditive à conduction aérienne d'un modèle particulier aux fins d'assurance de la qualité de la production, de l'approvisionnement et de la livraison. Le fabricant fixera normalement des valeurs nominales.

Elektroakustika – Slušni pripomočki – 7. del: Merjenje zmogljivostnih karakteristik slušnih pripomočkov za zagotavljanje kakovosti pri proizvodnji, oskrbi in dostavi (IEC 60118-7:2005)

General Information

Status
Published
Publication Date
28-Feb-2006
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
01-Mar-2006
Due Date
01-Mar-2006
Completion Date
01-Mar-2006

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SLOVENSKI SIST EN 60118-7:2006
STANDARD
marec 2006
Elektroakustika – Slušni pripomočki – 7. del: Merjenje zmogljivostnih
karakteristik slušnih pripomočkov za zagotavljanje kakovosti pri proizvodnji,
oskrbi in dostavi (IEC 60118-7:2005)
Electroacoustics – Hearing aids – Part 7: Measurement of the performance
characteristics of hearing aids for production, supply and delivery quality
assurance purposes (IEC 60118-7:2005)
ICS 11.180.15 Referenčna številka
SIST EN 60118-7:2006(en)

© Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

---------------------- Page: 1 ----------------------
EUROPEAN STANDARD EN 60118-7
NORME EUROPÉENNE
EUROPÄISCHE NORM December 2005
ICS 17.140.50 Supersedes EN 60118-7:1993 + A1:1994
English version
Electroacoustics –
Hearing aids
Part 7: Measurement of the performance characteristics of hearing aids
for production, supply and delivery quality assurance purposes
(IEC 60118-7:2005)
Electroacoustique – Akustik –
Appareils de correction auditive Hörgeräte
Partie 7: Mesure des caractéristiques Teil 7: Messung der
fonctionnelles des appareils de correction Übertragungseigenschaften von
auditive aux fins d'assurance de la qualité Hörgeräten zum Zwecke der
de la production, de la livraison Qualitätssicherung in der Herstellung,
et des approvisionnements Versorgung und Lieferung
(CEI 60118-7:2005) (IEC 60118-7:2005)

This European Standard was approved by CENELEC on 2005-12-01. CENELEC members are bound to

comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European

Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on

application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other

language made by translation under the responsibility of a CENELEC member into its own language and

notified to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, Czech

Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,

Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden,

Switzerland and United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2005 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 60118-7:2005 E
---------------------- Page: 2 ----------------------
EN 60118-7:2005 - 2 -
Foreword

The text of document 29/585/FDIS + 29/587/INF, future edition 2 of IEC 60118-7, prepared by

IEC TC 29, Electroacoustics, was submitted to the IEC-CENELEC parallel vote and was approved by

CENELEC as EN 60118-7 on 2005-12-01.
This European Standard supersedes EN 60118-7:1993 + A1:1994.

This European Standard includes major changes, e.g. regarding the definition of reference test gain.

In general this edition aligns IEC 60118-7 and the ANSI S3.22 (2003) standard.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2006-09-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2008-12-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice

The text of the International Standard IEC 60118-7:2005 was approved by CENELEC as a European

Standard without any modification.

In the official version, for Bibliography, the following notes have to be added for the standards indicated:

IEC 60068 NOTE Harmonized in the EN 60068 series (not modified).
IEC 60118-0 NOTE Harmonized as EN 60118-0:1993 (not modified).
IEC 60118-1 NOTE Harmonized as EN 60118-1:1995 (not modified).
IEC 60118-2 NOTE Harmonized as EN 60118-2:1995 (not modified).
__________
---------------------- Page: 3 ----------------------
- 3 - EN 60118-7:2005
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

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.

NOTE Where an international publication has been modified by common modifications, indicated by (mod), the relevant

EN/HD applies.
Publication Year Title EN/HD Year
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
At draft stage.
---------------------- Page: 4 ----------------------
NORME CEI
INTERNATIONALE
IEC
60118-7
INTERNATIONAL
Deuxième édition
STANDARD
Second edition
2005-10
Electroacoustique –
Appareils de correction auditive –
Partie 7:
Mesure des caractéristiques fonctionnelles
des appareils de correction auditive aux fins
d'assurance de la qualité de la production,
de la livraison et des approvisionnements
Electroacoustics –
Hearing aids –
Part 7:
Measurement of the performance characteristics
of hearing aids for production, supply and
delivery quality assurance purposes
 IEC 2005 Droits de reproduction réservés  Copyright - all rights reserved

Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in any

utilisée sous quelque forme que ce soit et par aucun procédé, form or by any means, electronic or mechanical, including

électronique ou mécanique, y compris la photocopie et les photocopying and microfilm, without permission in writing from

microfilms, sans l'accord écrit de l'éditeur. the publisher.

International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland

Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch

CODE PRIX
PRICE CODE
Commission Electrotechnique Internationale
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
Pour prix, voir catalogue en vigueur
For price, see current catalogue
---------------------- Page: 5 ----------------------
60118-7  IEC:2005 – 3 –
CONTENTS

FOREWORD...........................................................................................................................5

1 Scope...............................................................................................................................9

2 Normative references .......................................................................................................9

3 Terms and definitions .......................................................................................................9

4 General conditions .........................................................................................................15

5 Nominal characteristics and tolerances...........................................................................17

6 Test box and test equipment...........................................................................................17

7 Test conditions ...............................................................................................................21

8 Measurements, specifications and tolerances.................................................................29

9 Maximum permitted expanded uncertainty of measurements ..........................................43

Bibliography..........................................................................................................................45

Figure 1 – Example of test arrangement for behind the ear hearing aid.................................23

Figure 2 – Example of test arrangement for in-the-ear hearing aid ........................................25

Figure 3 – Example of OSPL90 and basic frequency response curves ..................................31

Figure 4 – Example of basic frequency response curve, its tolerances and

determination of frequency range..........................................................................................35

Table 1 – Resistance and open circuit voltages for battery simulator ....................................27

Table 2 – Tolerances of the frequency response...................................................................35

Table 3 – Distortion test frequencies and input sound pressure levels...................................37

Table 4 – Values of U for basic measurements...............................................................43

max
---------------------- Page: 6 ----------------------
60118-7 © IEC:2005 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTROACOUSTICS – HEARING AIDS –
Part 7: Measurement of the performance characteristics
of hearing aids for production, supply and delivery
quality assurance purposes
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

this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,

Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC

Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested

in the subject dealt with may participate in this preparatory work. International, governmental and non-

governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely

with the International Organization for Standardization (ISO) in accordance with conditions determined by

agreement between the two organizations.

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

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence

between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

the latter.

5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any

equipment declared to be in conformity with an IEC Publication.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

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 60118-7 has been prepared by IEC technical committee 29:

Electroacoustics.

This second edition cancels and replaces the first edition published in 1983. This technical

revision includes major changes eg. regarding the definition of reference test gain. In general

this edition aligns IEC 60118-7 and the ANSI S3.22 (2003) standard.
---------------------- Page: 7 ----------------------
60118-7  IEC:2005 – 7 –
The text of this standard is based on the following documents:
FDIS Report on voting
29/585/FDIS 29/590/RVD

Full information on the voting for the approval of this 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.

IEC 60118 consists of the following parts, under the general title Electroacoustics – Hearing

aids :
Part 0: Measurement of electroacoustical characteristics
Part 1: Hearing aids with induction pick-up coil input
Part 2: Hearing aids with automatic gain control circuits
Part 3: Hearing aid equipment not entirely worn on the listener

Part 4: Magnetic field strength in audio-frequency induction loops for hearing aid

purposes
Part 5: Nipples for insert earphones
Part 6: Characteristics of electrical input circuits for hearing aids

Part 7: Measurement of the performance characteristics of hearing aids for production,

supply and delivery quality assurance purposes

Part 8: Methods of measurement of performance characteristics of hearing aids under

simulated in situ working conditions

Part 9: Methods of measurement of characteristics of hearing aids with bone vibrator

output
Part 11: Symbols and other markings on hearing aids and related equipment
Part 12: Dimensions of electrical connector systems
Part 13: Electromagnetic compatibility (EMC)
Part 14: Specification of a digital interface device

The committee has decided that the contents of this publication will remain unchanged until

the maintenance result 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.
———————

Various parts of the series were published under the general title Hearing aids. Future editions of these parts

will appear under the new general title.
---------------------- Page: 8 ----------------------
60118-7  IEC:2005 – 9 –
ELECTROACOUSTICS – HEARING AIDS –
Part 7: Measurement of the performance characteristics
of hearing aids for production, supply and delivery
quality assurance purposes
1 Scope

This part of IEC 60118 gives recommendations for the measurement of the performance

characteristics of air-conduction hearing aids of a particular model for production, supply and

delivery quality assurance purposes. The manufacturer will normally assign nominal values.

This standard does not relate to mechanical or environmental tests. It should not be used as

the basis for the exchange of information about hearing aid characteristics in general, nor is it

intended to be used as a predictor for real-ear performance.

NOTE Terms such as "manufacturer" and "purchaser" are used in this standard. These terms may be understood,

however, to refer to the supplier and recipient respectively in any arrangement for the supply of hearing aids in

which the use of this standard is called for.

Though the number of measurements covered by this standard is limited, it is not intended

that all measurements described herein shall be made in every case.

This second edition now specifies performance requirements. Conformance to the specifi-

cations in this standard is demonstrated only when the result of a measurement, extended by

the actual expanded uncertainty of measurement of the testing laboratory, lies fully within the

tolerances specified in this standard extended by the values for U given in Table 4.

max

In case of custom-made in-the-ear instruments, the data supplied by the manufacturer applies

only to the particular hearing aid being tested.
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 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
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply:
———————

To be published. IEC 60318-5 is a revision of IEC 60126:1973, IEC reference coupler for the measurement of

hearing aids using earphones coupled to the ear by means of ear inserts.
---------------------- Page: 9 ----------------------
60118-7  IEC:2005 – 11 –
3.1
sound pressure level
SPL

all sound pressure levels specified are measured in decibels (dB) referenced to 20 µPa

3.2
high-frequency average
HFA
average of gain or SPL in decibels at 1 000 Hz, 1 600 Hz and 2 500 Hz
3.3
special purpose hearing aid

hearing aid whose full-on gain at any frequency exceeds its full-on gain at 1 000 Hz, or at

1 600 Hz or at 2 500 Hz by more than 15 dB. If the requirements for being a special purpose

hearing aid are met, the manufacturer may substitute the SPA for the HFA

NOTE The frequencies used for the SPA should be specified by the manufacturer and used for all measurements.

3.4
special purpose average
SPA

average of gain or SPL in dB at 3 special purpose frequencies for a special purpose hearing

aid. The manufacturer shall specify and state three special purpose one-third-octave-band

frequencies each separated by two-third octave

NOTE Throughout this standard, wherever the term HFA appears, SPA may be substituted for these aids.

3.5
acoustic gain

at each test frequency, the difference in decibels obtained by subtracting the input SPL to the

hearing aid microphone from the SPL developed by the output from the hearing aid in the

acoustic coupler
3.6
gain control
manually or electronically operated control for the adjustment of overall gain
3.7
output SPL for 90-dB input SPL
OSPL90

SPL developed in the acoustic coupler with an input SPL of 90 dB with the gain control of the

hearing aid full-on

NOTE 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 single input

SPL of 90 dB makes automatic recording of the OSPL90 curve very convenient.
---------------------- Page: 10 ----------------------
60118-7  IEC:2005 – 13 –
3.8
high-frequency average OSPL90
HFA-OSPL90
high-frequency average of the OSPL90 SPL levels
3.9
high-frequency average full-on gain
HFA-FOG

HFA gain for an input SPL of 50 dB when the gain control of the hearing aid is at its full-on

position
3.10
reference test setting of the gain control
RTS

for an input SPL of 60 dB, the setting of the gain control required to produce an HFA-gain

within ±1,5 dB of the HFA-OSPL90 minus 77 dB. If the full-on HFA gain for an input SPL of

60 dB is less than the HFA-OSPL90 minus 77 dB, the RTS is the full-on position of the gain

control

NOTE For linear hearing aids, the use of an input SPL of 60 dB and a 17 dB gain control setback from the

OSPL90 helps to ensure that, for an overall speech level of 65 dB SPL, peaks should not exceed the OSPL90.

3.11
reference test gain
RTG
HFA gain for an input SPL of 60 dB with the gain control at RTS
3.12
input-output function

single frequency plot of acoustic coupler SPL on the ordinate as a function of input SPL on

the abscissa with equal decibel scale divisions on each axis
3.13
automatic gain control
AGC

means (other than peak clipping) by which the gain is automatically controlled as a function of

the level of the signal being amplified
3.14
AGC hearing aid
hearing aid incorporating automatic gain control (AGC)
3.15
directional hearing aid

hearing aid for which the gain is dependent on the direction of sound incidence when

measured under free-field conditions
---------------------- Page: 11 ----------------------
60118-7  IEC:2005 – 15 –
3.16
non-directional hearing aid

hearing aid for which the gain is independent of the direction of sound incidence when

measured under free-field conditions
3.17
SPL in a magnetic field
SPLI

SPL developed in the acoustic coupler with the gain control at RTS when the input is −30 dB

re 1 A/m (=31,6 mA/m) sinusoidal alternating magnetic field and the input selector of the

hearing aid is in T-position (see 8.8)
3.18
high frequency average SPL in a magnetic field
HFA-SPLI
high-frequency average of the SPLI SPL levels
3.19
equivalent test loop sensitivity
ETLS
difference obtained by subtracting the (RTG + 60 dB) from the HFA-SPLI
4 General conditions
4.1 Acoustic test method

The preferred acoustic test procedure is based on a method of measurement in which the

sound pressure level at the reference point of the hearing aid is kept constant. This is

accomplished in an 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 designated "constant entrance sound pressure method" or shortened
"pressure method" throughout this standard.

As an alternative to the pressure method, storage of a test box frequency response correction

curve may be used. This method is designated “substitution method”.

The sound output from the hearing aid is coupled to the IEC acoustic coupler according to

IEC 60318-5.

NOTE 1 The test results may differ substantially from those obtained under free-field conditions, especially for

body-worn types of hearing aids having the sound entry located on a surface of the outer housing the physical

dimensions of which are comparable to the wavelength of the incident sound.

NOTE 2 For measuring the variation of acoustical parameters of hearing aids as a function of the direction of

sound incidence, progressive wave conditions are required. Small acoustic test boxes in which progressive wave

conditions are not present cannot be used for this purpose.
---------------------- Page: 12 ----------------------
60118-7  IEC:2005 – 17 –

NOTE 3 For testing directional hearing aids, manufacturer and purchaser should use acoustic test boxes of the

same make and type to secure identical measurement conditions. The results from such measurements may not

represent the true directional characteristics of the hearing aid.
4.2 Reporting of data
All data reported shall be clearly labelled: "According to IEC 60118-7:2005".
5 Nominal characteristics and tolerances

The characteristics with the prefix "nominal" listed below are those that are assigned by the

manufacturer for the hearing aid model in question (see also Figure 1 and Figure 2) and are

subject to verification, using the methods described in this standard:
– nominal reference test gain (see 3.11);
– nominal OSPL90 (see 8.2);
– nominal maximum OSPL90 (see 8.2);
– nominal full-on gain (see 8.3);
– nominal frequency response curve (see 8.4);
– nominal bandwidth frequencies f + f (see 8.4.2);
1 2
– nominal battery or supply voltage (see 7.3.2);
– nominal battery current (see 8.5);
– nominal total harmonic distortion (see 8.6);
– nominal equivalent input noise level (see 8.7);
– nominal equivalent test loop sensitivity (see 8.8.1);
– nominal maximum magneto acoustical sensitivity level (MASL) (see 8.8.2);
– nominal steady state input-output AGC characteristics (see 8.9.2);
– nominal attack- and release time (see 8.9.3).
6 Test box and test equipment
6.1 General
The following conditions should be met, for ambient conditions stated in 7.3.4.
6.2 Unwanted stimuli in the test box

Unwanted stimuli in the test box, 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,

when the signal source is switched off.
---------------------- Page: 13 ----------------------
60118-7  IEC:2005 – 19 –
6.3 Sound source

6.3.1 The sound source (pure tone), in combination with a pressure-calibrated controlling

microphone, shall be capable of producing at the test point the requisite sound pressure

levels between 50 dB and 90 dB, with a minimum step size of 5 dB, within a tolerance of

± 1,5 dB over the frequency range 200 Hz to 2 000 Hz and within ±2,5 dB over the range

2 000 Hz to 5 000 Hz.

If the calibration of the sound source depends on ambient conditions, corrections for such

dependence shall be made when necessary.

6.3.2 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.

6.3.3 For frequency response and full-on gain measurements, the total harmonic distortion of

the acoustic signal shall not exceed 2 %.

For harmonic distortion measurements, the total harmonic distortion of the acoustic signal up

to a sound pressure level of 70 dB shall not exceed 0,5 %.
6.4 Acoustic coupler

The IEC reference coupler in accordance with IEC 60318-5 shall be used. For behind-the-ear

type hearing aids, sound leakage from the coupling tube shall be low enough not to affect the

test result. The dimensions of the tubing shall be maintained in accordance with IEC 60318-5.

NOTE One way of accomplishing this is to use a rigid tube.
6.5 Measurement system for the measurement of sound pressure level and harmonic
distortion in the acoustic coupler

The equipment for the measurement of the coupler sound pressure level produced by the

hearing aid shall fulfil the following requirements:

a) the sound pressure level measurement system shall be accurate within ±1,0 dB at the

frequency of calibration;

b) the indication of sound pressure level in the acoustic coupler relative to the indication at

the frequency of calibration shall be measured with an expanded uncertainty of no more

than ±1,0 dB in the frequency range 200 Hz to 5 000 Hz;

If, under certain conditions, it is necessary to use a selective measuring system in order to

ensure that the response of the hearing aid to the signal can be differentiated from

inherent noise in the hearing aid, the use of the selective system shall be stated in the test

report.
Direct current measurement system:
The direct-current measuring system shall have the following characteristics:
a) a tolerance 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 5 000 Hz.

NOTE One method of realizing item c) above is to bypass the current meter with an 8 000 µF capacitor. The

capacitor should not shunt the battery or the power supply.
---------------------- Page: 14 ----------------------
60118-7  IEC:2005 – 21 –
7 Test conditions
7.1 General

Procedures for controlling the sound field and establishing test conditions for the hearing aid

are described below.
7.2 Control of the sound field
7.2.1 The input SPL at the hearing aid reference point is kept constant:
a) by means of a control microphone (pressure method – see 7.2.2);
b) with electronic data storage (substitution method – see 7.2.3).

7.2.2 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 it. For a 15 mm or

smaller diameter microphone, the distance from the centre of the diaphragm to the reference

point shall be 5 mm ± 3 mm. Figures 1 and 2 show examples of test arrangements.
---------------------- Page: 15 ----------------------
60118-7  IEC:2005 – 23 –
5 mm ± 3 mm
IEC 1650/05
Key
1 test space
2 sound source
3 hearing aid
4 control microphone
5 diaphragm
6 acoustic coupler

7 reference point of hearing aid. The axis of the control microphone shall be orthogonal to the speaker axis and

shall intersect it at the midpoint of the hearing aid sound inlet port or port array. A line through the front and

rear sound inlet ports of the hearing aid shall coincide with the speaker axis. In the case of multiple front or rear entry

ports, the line is passed through the midpoint of the port array.
8 tubing 25 mm length, ø 2 mm in accordance with IEC 60318-5
Figure 1 – Example of test arrangement for behind the ear hearing aid
---------------------- Page: 16 ----------------------
60118-7  IEC:2005 – 25 –
5 mm ± 3 mm
6 3
IEC 1651/05
Key
1 test space
2 sound sour
...

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