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)
Standards Content (Sample)
SLOVENSKI SIST EN 60118-7:2006
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
EUROPÄISCHE NORM December 2005
ICS 17.140.50 Supersedes EN 60118-7:1993 + A1:1994
Part 7: Measurement of the performance characteristics of hearing aids
for production, supply and delivery quality assurance purposes
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 EuropeanStandard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained onapplication 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.
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
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EN 60118-7:2005 - 2 -
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 byCENELEC 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.
The text of the International Standard IEC 60118-7:2005 was approved by CENELEC as a EuropeanStandard 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).
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- 3 - EN 60118-7:2005
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 referenceddocument (including any amendments) applies.
NOTE Where an international publication has been modified by common modifications, indicated by (mod), the relevantEN/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.
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Appareils de correction auditive –
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
Hearing aids –
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 frommicrofilms, 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: firstname.lastname@example.org Web: www.iec.chCODE PRIX
Commission Electrotechnique Internationale
International Electrotechnical Commission
Pour prix, voir catalogue en vigueur
For price, see current catalogue
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60118-7 IEC:2005 – 3 –
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
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 ..................................31Figure 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...............................................................43max
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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
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 byagreement 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 allinterested 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 anymisinterpretation 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 inthe latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for anyequipment 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 IECPublications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications isindispensable 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 generalthis edition aligns IEC 60118-7 and the ANSI S3.22 (2003) standard.
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60118-7 IEC:2005 – 7 –
The text of this standard is based on the following documents:
FDIS Report on voting
Full information on the voting for the approval of this standard can be found in the report onvoting 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 – Hearingaids :
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 aidpurposes
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 undersimulated in situ working conditions
Part 9: Methods of measurement of characteristics of hearing aids with bone vibratoroutput
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;
• replaced by a revised edition, or
Various parts of the series were published under the general title Hearing aids. Future editions of these partswill appear under the new general title.
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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
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 itintended 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 inwhich the use of this standard is called for.
Though the number of measurements covered by this standard is limited, it is not intendedthat 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 appliesonly 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 editionof 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 earinserts
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 ofhearing aids using earphones coupled to the ear by means of ear inserts.
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60118-7 IEC:2005 – 11 –
sound pressure level
all sound pressure levels specified are measured in decibels (dB) referenced to 20 µPa3.2
average of gain or SPL in decibels at 1 000 Hz, 1 600 Hz and 2 500 Hz
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 purposehearing 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
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-bandfrequencies each separated by two-third octave
NOTE Throughout this standard, wherever the term HFA appears, SPA may be substituted for these aids.3.5
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 theacoustic coupler
manually or electronically operated control for the adjustment of overall gain
output SPL for 90-dB input SPL
SPL developed in the acoustic coupler with an input SPL of 90 dB with the gain control of thehearing 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 inputSPL of 90 dB makes automatic recording of the OSPL90 curve very convenient.
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60118-7 IEC:2005 – 13 –
high-frequency average OSPL90
high-frequency average of the OSPL90 SPL levels
high-frequency average full-on gain
HFA gain for an input SPL of 50 dB when the gain control of the hearing aid is at its full-onposition
reference test setting of the gain control
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 gaincontrol
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
HFA gain for an input SPL of 60 dB with the gain control at RTS
single frequency plot of acoustic coupler SPL on the ordinate as a function of input SPL onthe abscissa with equal decibel scale divisions on each axis
automatic gain control
means (other than peak clipping) by which the gain is automatically controlled as a function ofthe level of the signal being amplified
AGC hearing aid
hearing aid incorporating automatic gain control (AGC)
directional hearing aid
hearing aid for which the gain is dependent on the direction of sound incidence whenmeasured under free-field conditions
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60118-7 IEC:2005 – 15 –
non-directional hearing aid
hearing aid for which the gain is independent of the direction of sound incidence whenmeasured under free-field conditions
SPL in a magnetic field
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 thehearing aid is in T-position (see 8.8)
high frequency average SPL in a magnetic field
high-frequency average of the SPLI SPL levels
equivalent test loop sensitivity
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 thehearing 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 correctioncurve may be used. This method is designated “substitution method”.
The sound output from the hearing aid is coupled to the IEC acoustic coupler according toIEC 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 physicaldimensions 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 waveconditions are not present cannot be used for this purpose.
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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 notrepresent 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 aresubject 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);
– 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
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.
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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 range2 000 Hz to 5 000 Hz.
If the calibration of the sound source depends on ambient conditions, corrections for suchdependence 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 ofthe acoustic signal shall not exceed 2 %.
For harmonic distortion measurements, the total harmonic distortion of the acoustic signal upto 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 thehearing aid shall fulfil the following requirements:
a) the sound pressure level measurement system shall be accurate within ±1,0 dB at thefrequency 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 morethan ±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 testreport.
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. Thecapacitor should not shunt the battery or the power supply.
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60118-7 IEC:2005 – 21 –
7 Test conditions
Procedures for controlling the sound field and establishing test conditions for the hearing aidare 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 referencepoint shall be 5 mm ± 3 mm. Figures 1 and 2 show examples of test arrangements.
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60118-7 IEC:2005 – 23 –
5 mm ± 3 mm
1 test space
2 sound source
3 hearing aid
4 control microphone
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 entryports, 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
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60118-7 IEC:2005 – 25 –
5 mm ± 3 mm
1 test space
2 sound sour