SIST EN 60318-4:2010

SLOVENSKI STANDARD
SIST EN 60318-4:2010
01-september-2010
1DGRPHãþD
SIST HD 443 S1:2004
(OHNWURDNXVWLND6LPXODWRUMLþORYHãNHJODYHLQXãHVGHO6LPXODWRU]DPDãHQHJD
XãHVD]DPHUMHQMHXãHVQLKVOXãDONVSRMHQLK]XãHVRPSUHNXãHVQLKYVWDYNRY,(&

Electroacoustics - Simulators of human head and ear - Part 4: Occluded-ear simulator for
the measurement of earphones coupled to the ear by means of ear inserts (IEC 60318-
4:2010)
Akustik - Simulatoren des menschlichen Kopfes und Ohres - Teil 4: Simulator für den
abgeschlossenen Gehörgang zur Messung an mittels Ohreinsätzen an das Ohr
angekoppelten Ohrhörern (IEC 60318-4:2010)
Electroacoustique - Simulateurs de tête et d'oreille humaines - Partie 4: Simulateur
d'oreille occluse pour la mesure des écouteurs couplés à l'oreille par des embouts (CEI
60318-4:2010)
Ta slovenski standard je istoveten z: EN 60318-4:2010
ICS:
13.140 Vpliv hrupa na ljudi Noise with respect to human
beings
17.140.50 Elektroakustika Electroacoustics
SIST EN 60318-4:2010 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------

SIST EN 60318-4:2010

---------------------- Page: 2 ----------------------

SIST EN 60318-4:2010

EUROPEAN STANDARD
EN 60318-4

NORME EUROPÉENNE
May 2010
EUROPÄISCHE NORM

ICS 17.140.50 Supersedes HD 443 S1:1983


English version


Electroacoustics -
Simulators of human head and ear -
Part 4: Occluded-ear simulator for the measurement of earphones coupled
to the ear by means of ear inserts
(IEC 60318-4:2010)


Electroacoustique -  Akustik -
Simulateurs de tête et d'oreille humaines - Simulatoren des menschlichen Kopfes
Partie 4: Simulateur d'oreille occluse und Ohres -
pour la mesure des écouteurs couplés Teil 4: Simulator für den abgeschlossenen
à l'oreille par des embouts Gehörgang zur Messung an mittels
(CEI 60318-4:2010) Ohreinsätzen an das Ohr angekoppelten
Ohrhörern
(IEC 60318-4:2010)




This European Standard was approved by CENELEC on 2010-05-01. 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, Bulgaria, Croatia, Cyprus,
the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,
Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia,
Spain, Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Management Centre: Avenue Marnix 17, B - 1000 Brussels


© 2010 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60318-4:2010 E

---------------------- Page: 3 ----------------------

SIST EN 60318-4:2010
EN 60318-4:2010 - 2 -
Foreword
The text of document 29/662/CDV, future edition 1 of IEC 60318-4, prepared by IEC TC 29,
Electroacoustics, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 60318-4 on 2010-05-01.
This standard supersedes HD 443 S1:1983.
The main changes with respect to the previous edition are listed below:
− extension of the usable frequency range to 100 Hz – 16 000 Hz;
− addition of values of maximum permitted expanded uncertainties to all tolerances.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN and CENELEC shall not be held responsible for identifying any or all such patent
rights.
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) 2011-02-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2013-05-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 60318-4:2010 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:
[1]  ISO 389-2 NOTE  Harmonized as EN ISO 389-2.
[2]  ISO 389-5 NOTE  Harmonized as EN ISO 389-5.
[3]  ISO 389-6 NOTE  Harmonized as EN ISO 389-6.
__________

---------------------- Page: 4 ----------------------

SIST EN 60318-4:2010
- 3 - EN 60318-4:2010
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  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.

Publication Year Title EN/HD Year

IEC 61094-4 - Measurement microphones - EN 61094-4 -
Part 4: Specifications for working standard
microphones


ISO/IEC Guide 98-3 - Uncertainty of measurement - - -
Part 3: Guide to the expression of uncertainty
in measurement (GUM:1995)

---------------------- Page: 5 ----------------------

SIST EN 60318-4:2010

---------------------- Page: 6 ----------------------

SIST EN 60318-4:2010
IEC 60318-4
®
Edition 1.0 2010-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE


Electroacoustics – Simulators of human head and ear –
Part 4: Occluded-ear simulator for the measurement of earphones coupled to
the ear by means of ear inserts

Électroacoustique – Simulateurs de tête et d’oreille humaines –
Partie 4: Simulateur d'oreille occluse pour la mesure des écouteurs couplés à
l'oreille par des embouts

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
R
CODE PRIX
ICS 17.140.50 ISBN 2-8318-1076-6
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

---------------------- Page: 7 ----------------------

SIST EN 60318-4:2010
– 2 – 60318-4 © IEC:2010
CONTENTS
FOREWORD.3
1 Scope.5
2 Normative references .5
3 Terms and definitions .5
4 Construction .7
4.1 General .7
4.2 Principal cavity dimensions .7
4.3 Calibrated pressure-type microphone .7
4.4 Pressure equalization.8
4.5 Acoustic transfer impedance level .8
4.6 Example of design.8
5 Calibration.9
5.1 Atmospheric reference conditions.9
5.2 Calibration method .9
6 Coupling of earphones and hearing aids to the occluded-ear simulator.9
6.1 Audiometers with insert earphones.9
6.2 In-the-ear hearing aids (custom made) .9
6.3 Hearing aids with insert earphone .10
6.4 Behind-the-ear and spectacle hearing aids.11
6.5 Modular in-the-ear hearing aids.12
7 Maximum permitted expanded uncertainty of measurements .14
Annex A (informative) Example of one specific design of occluded-ear simulator .16
Annex B (informative) Principle of calibration for the occluded-ear simulator.17
Bibliography.19

Figure 1 – Connection of an in-the-ear hearing aid to the occluded-ear simulator .10
Figure 2 – Connection of an insert earphone to the occluded-ear simulator .11
Figure 3 – Connection of a behind-the-ear hearing aid to the occluded-ear simulator.13
Figure 4 – Connection of an in-the-ear hearing aid (modular type) to the occluded-ear
simulator.14
Figure A.1 – Example of one specific design of occluded-ear simulator.16

Table 1 – Level of the acoustic transfer impedance modulus and associated tolerances .8
Table 2 – Values of maximum permitted expanded uncertainty U for basic type
max
approval measurements.15
Table B.1 – Sound pressure level relative to that at the reference frequency 500 Hz
3
(L (f)– L (500)) for the nominal effective volume (1 260 mm ) of the occluded-ear
p p
simulator, and associated tolerances .18

---------------------- Page: 8 ----------------------

SIST EN 60318-4:2010
60318-4 © IEC:2010 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

ELECTROACOUSTICS –
SIMULATORS OF HUMAN HEAD AND EAR –

Part 4: Occluded-ear simulator for the measurement
of earphones coupled to the ear by means of ear inserts


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 itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
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 60318-4 has been prepared by IEC technical committee 29:
Electroacoustics.
This first edition of IEC 60318-4 cancels and replaces IEC 60711, published in 1981 and
constitutes a technical revision.
The main changes with respect to the previous edition are listed below:
– extension of the usable frequency range to 100 Hz – 16 000 Hz;
– addition of values of maximum permitted expanded uncertainties to all tolerances.

---------------------- Page: 9 ----------------------

SIST EN 60318-4:2010
– 4 – 60318-4 © IEC:2010
The text of this standard is based on the following documents:
Enquiry draft Report on voting
29/662/CDV 29/685/RVC

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.
A list of all parts of the IEC 60318 series can be found on the IEC website under the title:
Electroacoustics – Simulators of human head and ear.
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.

---------------------- Page: 10 ----------------------

SIST EN 60318-4:2010
60318-4 © IEC:2010 – 5 –
ELECTROACOUSTICS –
SIMULATORS OF HUMAN HEAD AND EAR –

Part 4: Occluded-ear simulator for the measurement
of earphones coupled to the ear by means of ear inserts



1 Scope
This part of IEC 60318 describes an occluded-ear simulator intended for the measurement of
insert earphones in the frequency range from 100 Hz to 10 000 Hz. It is suitable for air
conduction hearing aids and earphones, coupled to the ear by means of ear inserts e.g. ear
moulds or similar devices. The occluded-ear simulator is also suitable as the basis for an
extension intended to simulate the complete ear canal and the outer ear (for instance in head
simulators).
The occluded-ear simulator simulates the acoustic transfer impedance for the occluded
normal adult human ear. However, it does not simulate the leakage between an earmould and
a human ear canal; therefore, the results obtained with the occluded-ear simulator may
deviate from the performance of an insert earphone on a real ear, especially at low
frequencies. Moreover, large performance variations among individual ears will occur which
should be considered when using the ear simulator.
Above 10 kHz the device does not simulate a human ear, but can be used as an acoustic
coupler at additional frequencies up to 16 kHz. Below 100 Hz, the device has not been
verified to simulate a human ear, but can be used as an acoustic coupler at additional
frequencies down to 20 Hz.
NOTE Due to resonances in the acoustic transfer impedance of the occluded-ear simulator above 10 kHz, high
measurement uncertainties, e.g. in the order of 10 dB, can occur in earphone responses. Repeatable results mainly
are obtained for insert earphones with high acoustic damping (used for instance in the extended high-frequency
1
audiometry, see the earphones listed in ISO 389-6)[3] coupled to the occluded-ear simulator by means of a
simple, symmetrically designed and air tight coupling device.
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 61094-4, Measurement microphones – Part 4: Specifications for working standard
microphones
ISO/IEC Guide 98-3, Uncertainty of measurement – Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
___________
1
Figures in square brackets refer to the Bibliography.

---------------------- Page: 11 ----------------------

SIST EN 60318-4:2010
– 6 – 60318-4 © IEC:2010
3.1
ear insert
device used to provide the acoustic coupling between an earphone and the ear canal (e.g. an
earmould or a similar device with or without a connecting tube)
3.2
insert earphone
small earphone coupled to the ear canal by means of an ear insert or attached to a
connecting element which is inserted into the ear canal
NOTE This ear insert may be a part of the insert earphone.
3.3
ear-mould simulator
ear insert simulator
insert which terminates the entrance of the ear simulator and provides for passage of sound
into the occluded-ear simulator through an opening on its axis
3.4
ear simulator
device for measuring the acoustic output of sound sources where the sound pressure is
measured by a calibrated microphone coupled to the source so that the overall acoustic
impedance of the device approximates that of the normal human ear at a given location and in
a given frequency band
3.5
occluded-ear simulator
ear simulator which approximates the acoustic transfer impedance of the inner part of the ear
canal, from the tip of an ear insert to the eardrum
3.6
acoustic coupler
device for measuring the acoustic output of sound sources where the sound pressure is
measured by a calibrated microphone coupled to the source by a cavity of predetermined
shape and volume which does not necessarily approximate the acoustical impedance of the
normal human ear
3.7
reference plane of the occluded-ear simulator
plane perpendicular to the axis of the cavity of the simulator, chosen to pass through the
position normally occupied by the tip of an earmould in a human ear
3.8
acoustic transfer impedance of the occluded-ear simulator
quotient of the sound pressure at the diaphragm of its microphone by the volume velocity
through the reference plane
–3
unit: Pa⋅s⋅m
3.9
acoustic transfer impedance level of the occluded-ear simulator
ten times the logarithm to the base of ten of the quotient of the absolute value (modulus) of
the squared acoustic transfer impedance of the occluded-ear simulator by the squared
–3
reference acoustic transfer impedance of one pascal second per cubic metre (Pa⋅s⋅m )

unit: dB

---------------------- Page: 12 ----------------------

SIST EN 60318-4:2010
60318-4 © IEC:2010 – 7 –
3.10
effective volume
equivalent volume of air of the acoustic compliance of the ear simulator formed by the cavity
and the microphone at a frequency of 500 Hz
3
unit: mm
4 Construction
4.1 General
The occluded-ear simulator shall be constructed of hard, dimensionally stable, non-porous
and non-magnetic material. The general construction of the occluded-ear simulator and
mounting of the microphone shall aim at minimizing the response of the microphone to
vibration (for example from an earphone) or to extraneous sound outside the cavity.
NOTE 1 The external diameter of the occluded-ear simulator should be kept as small as possible in order to
minimize diffractional errors which might affect the measurements when the occluded-ear simulator has to be
placed in a free sound field.
NOTE 2 In order to avoid a possible sound attenuation caused by the dust protector (see Figure A.1), an
earphone calibration should be performed above 10 kHz at least every two years with the occluded-ear simulator
equipped with and without its dust protector in place. The two results should not differ by more than 0,2 dB at
frequencies up to 16 kHz. If this is not the case at some frequencies, earphone measurements at those frequencies
should generally be performed without the dust protector.
The construction of the occluded-ear simulator shall permit the location of a transducer at the
reference plane for calibrating the simulator.
Where tolerances are specified in this part of IEC 60318, these shall be reduced by an
amount equal to the actual expanded measurement uncertainty of the test laboratory before
deciding if a device conforms to the stated requirement.
4.2 Principal cavity dimensions
The diameter of the principal cavity shall be (7,50 ± 0,04) mm.
The length of the principal cavity shall be such as to produce a half-wavelength resonance of
the sound pressure at (13,5 ± 1,5) kHz.
4.3 Calibrated pressure-type microphone
A calibrated microphone is located at the base of principal cavity of the occluded-ear
simulator. The acoustic impedance of the microphone diaphragm shall be high, so that the
3
equivalent volume is less than 20 mm over the specified range of frequencies. The
microphone shall conform to the requirements of IEC 61094-4 for a type WS2P microphone.
The microphone shall be coupled to the principal cavity with a seal that prevents acoustic
leaks.
In the frequency range 20 Hz to 10 kHz, the overall sound pressure sensitivity level of the
microphone and associated measuring system shall be known with an uncertainty not
exceeding 0,3 dB for a level of confidence of 95 %. For measurements above 10 kHz, the
overall pressure sensitivity level of the microphone and associated measuring system over
the specified frequency range shall be known with an uncertainty not exceeding 0,5 dB for a
level of confidence of 95 %.
The make and model of the microphone shall be specified by the manufacturer of the
occluded-ear simulator.
NOTE The acoustic impedance of the microphone affects the overall acoustic impedance of the occluded-ear
simulator.

---------------------- Page: 13 ----------------------

SIST EN 60318-4:2010
– 8 – 60318-4 © IEC:2010
4.4 Pressure equalization
A vent shall be provided to equalize the static pressure in the cavity of the occluded-ear
–3
simulator. The vent shall have an acoustic resistance of (7,0 ± 5,5) GPa⋅s⋅m .
4.5 Acoustic transfer impedance level
The level of the acoustic transfer impedance modulus of the occluded-ear simulator and the
associated tolerances shall be as specified in Table 1.
NOTE 1 At 500 Hz, the specified transfer impedance level corresponds to the magnitude of the acoustic transfer
–3 3
and also to the magnitude of the effective volume 1 260 mm of the ear simulator.
impedance 35,9 MPa⋅s⋅m
NOTE 2 The tolerances have minimum values at the frequency 500 Hz, where the influence of leakage and wave
motion is small.
4.6 Example of design
An example of one specific design of occluded-ear simulator is shown in Annex A.
Table 1 – Level of the acoustic transfer impedance modulus
and associated tolerances
Acoustic transfer
Nominal
impedance level
frequency
–3
re 1 MPa⋅s⋅m in dB
Hz
Level Tolerances
100 44,8
± 0,7
125 42,9 ± 0,7
160 40,8 ± 0,7
200 39,0 ± 0,6
250 37,0
± 0,6
315 35,0
± 0,6
400 33,0 ± 0,6
500 31,1 ± 0,3
630 29,2 ± 0,6
800 27,2
± 0,6
1 000 26,7 ± 0,7
1 250 26,4 ± 0,7
1 600 25,5 ± 0,7
2 000 24,2
± 0,8
2 500 23,1
± 0,8
3 150 22,0
± 0,9
4 000 21,1 ± 1,0
5 000 20,4 ± 1,2
6 300 20,5 ± 1,2
8 000 20,8
± 1,7
10 000 23,1
± 2,2
NOTE 1 Using the measurement method described in Annex B, it is not easy to measure the acoustical transfer
impedance level below 100 Hz, due to the effects of an imperfectly sealed measurement configuration. However,
the acoustical transfer impedance between 20 Hz and 100 Hz is governed predominantly by the volumetric
elements of the occluded-ear simulator, and their contribution to the overall acoustical transfer impedance can be
validated by the measurements at higher frequencies.

---------------------- Page: 14 ----------------------

SIST EN 60318-4:2010
60318-4 © IEC:2010 – 9 –
n/10
NOTE 2 The values in Table 1 are valid for the exact one-third-octave frequencies calculated from 1 000 × 10 ,
where n is a positive or negative integer or zero.
5 Calibration
5.1 Atmospheric reference conditions
Reference ambient pressure: 101,325 kPa
Reference temperature: 23 °C
Reference relative humidity: 50 %
5.2 Calibration method
The manufacturer shall describe the method(s) for determining calibration and overall stability
of the complete occluded-ear simulator including the microphone in an instruction manual.
The method shall include the determination of the effective volume at 500 Hz.
The principle of calibration is given in Annex B.
The calibration should be performed for the atmospheric reference conditions given in 5.1 with
the following tolerances:
Ambient pressure: ± 3 kPa
Temperature: ± 3 °C
Relative humidity: ± 20 %
If it is not possible to perform the calibration at reference conditions, the calibration shall be
referred to the atmospheric reference conditions given in 5.1, see [8], [9].
6 Coupling of earphones and hearing aids to the occluded-ear simulator
6.1 Audiometers with insert earphones
Insert earphones with standardized reference equivalent threshold sound pressure levels
shall be connected to the occluded-ear simulator as specified in the relevant ISO standards.
For other earphones, the manufacturer of the audiometer shall describe the method of
connection.
NOTE Reference hearing threshold sound pressure levels of insert earphones for audiometers and its connection
to the occluded-ear simulator are standardized in ISO 389-2 [1], ISO 389-5 [2] and ISO 389-6 [3].
6.2 In-the-ear hearing aids (custom made)
The hearing aid shall be connected directly to the cavity of the occluded-ear simulator as
indicated in Figure 1. The connection between the hearing aid and the occluded-ear simulator
shall be made airtight by using a suitable seal. In doing so, care shall be taken not to
introduce additional volume to the cavity which can affect the measured performance of the
hearing aid.
In the same way, a hearing aid equipped with a separate ear insert can be measured.

---------------------- Page: 15 ----------------------

SIST EN 60318-4:2010
– 10 – 60318-4 © IEC:2010
Dimensions in millimetres
IEC  030/10

Key
a hearing aid (custom-made)
b airtight seal and support for hearing aid
c retaining collar
d reference plane
e tip of hearing aid or insert should lie in the reference plane
f occluded-ear simulator
NOTE 1 This diagram is only intended as a schematic representation illustrating the principle of connecting the
hearing aid to the occluded-ear simulator. Effective airtight seals should be assured at all connection points.
NOTE 2 In the same manner, a hearing aid equipped with a separate ear insert can be connected to the occluded
ear simulator.
Figure 1 – Connection of an in-the-ear hearing aid
to the occluded-ear simulator
6.3 Hearing aids with insert earphone
Where possible, the ear insert used with the human ear shall be replaced by an ear-mould
simulator consisting essentially of a rigid tube, coaxial with the cavity, of length 18,0 mm ±
0,20 mm and internal diameter 3,00 mm ± 0,06 mm, representing the tubular portion of an
average ear mould.
The connection between the nub of the earphone and the ear-mould simulator shall be made
airtight by using a suitable seal, In doing so, care shall be taken not to introduce additional
volume to the cavity which can a
...