SIST EN ISO 11904-1:2004

Acoustics - Determination of sound immission from sound sources placed close to the ear - Part 1: Technique using a microphone in a real ear (MIRE technique) (ISO 11904-1:2002)

The standard specifies methods for the measurement of the noise immision caused by the ear- or headphones of electroacoustical reproducing systems (eg. personal listening devices, dictating machines, voice radio communication systems for pilots etc., at workplaces inclusive environmental noise if applicable) and determination of correction factors to determine the free field exposure. Part 2 makes use of miniature microphones in the ear for closed headphones (including hearing protectors with communicating facilities.

Akustik - Bestimmung der Schallimmission von ohrnahen Schallquellen - Teil 1: Verfahren mit Mikrofonen in menschlichen Ohren (MIRE-Verfahren) (ISO 11904-1:2002)

Dieser Teil von ISO 11904 legt Rahmenmessverfahren für die Messung von Schallimmissionsmessungen durch ohrnahe Schallquellen fest. Diese Messungen werden mit Miniatur- oder Sondenmikrofonen in den Gehörgängen von Versuchspersonen durchgeführt. Die gemessenen Werte werden anschließend in entsprechende Freifeld- bzw. Diffusfeldpegel umgerechnet. Die Ergebnisse können werden als freifeldbezogene bzw. diffusfeldbezogene A-bewertete äquivalente Dauerschalldruckpegel angegeben werden. Das Verfahren wird als MIRE-Verfahren bezeichnet (MIRE = Microphone In Real Ear / Mikrofon im menschlichen Ohr).
Dieser Teil von ISO 11904 ist anwendbar auf die Exposition durch ohrnahe Schallquellen, beispielsweise bei Geräteprüfungen oder am Arbeitsplatz durch Ohrhörer oder Gehörschützer mit Sprachübertragungssystemen.
Dieser Teil von ISO 11904 ist anwendbar für den Frequenzbereich von 20 Hz bis 16 000 Hz.

Acoustique - Détermination de l'exposition sonore due a des sources sonores placées a proximité de l'oreille - Partie 1: Technique du microphone placé dans une oreille réelle (technique MIRE) (ISO 11904-1:2002)

L'ISO 11904-1:2002 spécifie des méthodes de mesure générales d'émissions sonores des sources de bruit placées à proximité de l'oreille. Ces mesurages sont effectués au moyen de microphones miniatures ou de sondes microphoniques insérés dans les conduits auditifs de sujets humains. Les valeurs mesurées sont ensuite converties en niveaux ramenés au champ libre ou au champ diffus correspondants. Les résultats sont donnés sous forme de niveaux de pression acoustique continus équivalents pondérés A relatifs au champ libre ou au champ diffus. La technique est appelée technique du microphone dans l'oreille réelle (technique MIRE).
L'ISO 11904-1:2002 peut s'appliquer à l'exposition à des sources placées à proximité de l'oreille, par exemple, au cours d'essais d'équipements ou au poste de travail, avec par exemple des écouteurs ou des protecteurs individuels contre le bruit munis de moyens de communication audio.
L'ISO 11904-1:2002 s'applique dans la gamme de fréquences comprises entre 20 Hz et 16 000 Hz.

Akustika - Določanje imisije zvoka od zvočnih virov v neposredni bližini ušesa – 1. del: Metoda z mikrofonom v ušesu (metoda MIRE ) (ISO 11904-1:2002)

General Information

• Status: Published
• Publication Date: 31-Dec-2003
• ICS: 17.140.01 - Acoustic measurements and noise abatement in general
• ICS: 33.160.50 - Accessories
• Technical Committee: AKU - Acoustics
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Jan-2004
• Due Date: 01-Jan-2004
• Completion Date: 01-Jan-2004
• Ref Project: EN ISO 11904-1:2002 - Acoustics - Determination of sound immission from sound sources placed close to the ear - Part 1: Technique using a microphone in a real ear (MIRE technique) (ISO 11904-1:2002)

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 11904-1:2004
01-januar-2004
$NXVWLND'RORþDQMHLPLVLMH]YRNDRG]YRþQLKYLURYYQHSRVUHGQLEOLåLQLXãHVD±
GHO0HWRGD]PLNURIRQRPYXãHVXPHWRGD0,5(,62
Acoustics - Determination of sound immission from sound sources placed close to the
ear - Part 1: Technique using a microphone in a real ear (MIRE technique) (ISO 11904-
1:2002)
Akustik - Bestimmung der Schallimmission von ohrnahen Schallquellen - Teil 1:
Verfahren mit Mikrofonen in menschlichen Ohren (MIRE-Verfahren) (ISO 11904-1:2002)
Acoustique - Détermination de l'exposition sonore due a des sources sonores placées a
proximité de l'oreille - Partie 1: Technique du microphone placé dans une oreille réelle
(technique MIRE) (ISO 11904-1:2002)
Ta slovenski standard je istoveten z: EN ISO 11904-1:2002
ICS:
17.140.01 $NXVWLþQDPHUMHQMDLQ Acoustic measurements and
EODåHQMHKUXSDQDVSORãQR noise abatement in general
33.160.50 Pribor Accessories
SIST EN ISO 11904-1:2004 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 11904-1:2004

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SIST EN ISO 11904-1:2004
EUROPEAN STANDARD
EN ISO 11904-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2002
ICS 17.140.01
English version
Acoustics - Determination of sound immission from sound
sources placed close to the ear - Part 1: Technique using a
microphone in a real ear (MIRE technique) (ISO 11904-1:2002)
Acoustique - Détermination de l'exposition sonore due à Akustik - Bestimmung der Schallimmission von ohrnahen
des sources sonores placées à proximité de l'oreille - Partie Schallquellen - Teil 1: Verfahren mit Mikrofonen in
1: Technique du microphone placé dans une oreille réelle menschlichen Ohren (MIRE-Verfahren) (ISO 11904-1:2002)
(technique MIRE) (ISO 11904-1:2002)
This European Standard was approved by CEN on 29 August 2002.
CEN 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 Management Centre or to any CEN 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 CEN member into its own language and notified to the Management Centre has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2002 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 11904-1:2002 E
worldwide for CEN national Members.

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SIST EN ISO 11904-1:2004
EN ISO 11904-1:2002 (E)
CORRECTED 2002-11-13
Foreword
This document (EN ISO 11904-1:2002) has been prepared by Technical Committee ISO/TC 43
"Acoustic " in collaboration with Technical Committee CEN/TC 211 "Acoustics", the secretariat of
which is held by DS.
This European Standard shall be given the status of a national standard, either by publication of
an identical text or by endorsement, at the latest by April 2003, and conflicting national
standards shall be withdrawn at the latest by April 2003.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium, Czech
Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg,
Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 11904-1:2002 has been approved by CEN as EN ISO 11904-1:2002 without any
modifications.
NOTE Normative references to International Standards are listed in Annex ZA (normative).
2

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SIST EN ISO 11904-1:2004
EN ISO 11904-1:2002 (E)
Annex ZA
(normative)
Normative references to international publications
with their relevant European publications
This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions of
any of these publications apply to this European Standard only when incorporated in it by
amendment or revision. For undated references the latest edition of the publication referred to
applies (including amendments).
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
ISO 8253-2 1992 Acoustics - Audiometric test methods - Part EN ISO 8253-2 1998
2: Sound field audiometry with pure tone and
narrow-band test signals
3

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SIST EN ISO 11904-1:2004

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SIST EN ISO 11904-1:2004


INTERNATIONAL ISO
STANDARD 11904-1
First edition
2002-10-01


Acoustics — Determination of sound
immission from sound sources placed
close to the ear —
Part 1:
Technique using a microphone in a real ear
(MIRE technique)
Acoustique — Détermination de l'exposition sonore due à des sources
sonores placées à proximité de l'oreille —
Partie 1: Technique du microphone placé dans une oreille réelle (technique
MIRE)




Reference number
ISO 11904-1:2002(E)
©
 ISO 2002

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SIST EN ISO 11904-1:2004
ISO 11904-1:2002(E)
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All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
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ii © ISO 2002 – All rights reserved

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SIST EN ISO 11904-1:2004
ISO 11904-1:2002(E)
Contents Page
Foreword . iv
Introduction. v
1 Scope. 1
2 Normative references. 1
3 Terms and definitions. 2
4 Measurement principle. 3
5 Instrumentation. 3
5.1 Ear canal microphone. 3
5.2 Reference field microphone. 4
5.3 Check of calibration. 4
5.4 Filters. 4
6 Subjects. 4
7 Use of ear canal microphone . 4
7.1 Choice of ear canal measurement position. 4
7.2 Mounting of microphones . 6
7.3 Safety. 6
8 Determination of free-field or diffuse-field related equivalent continuous A-weighted sound
pressure level . 6
8.1 Measurement of ear canal sound pressure level. 6
8.2 Conversion to free-field or diffuse-field related sound pressure level. 7
8.3 A-weighting and summation. 7
9 Free-field and diffuse-field frequency responses for selected ear canal measurement positions . 7
10 Determination of free-field or diffuse-field frequency responses. 7
10.1 General. 7
10.2 Measurement principle. 9
10.3 Establishment of a free reference sound field . 9
10.4 Establishment of a quasi-free reference sound field . 9
10.5 Establishment of a diffuse reference sound field. 9
10.6 Measurement of the reference sound field. 9
10.7 Measurement of ear canal sound pressure level in reference sound field . 9
10.8 Determination of free-field or diffuse-field frequency response.10
10.9 Simplifications in specific cases . 10
10.10 Optional check of the measurement arrangement . 10
11 Test report. 10
Annex A (informative) Example of sources of measurement uncertainty . 11
Annex B (informative) Example of an uncertainty analysis . 17
Bibliography. 19

© ISO 2002 – All rights reserved iii

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SIST EN ISO 11904-1:2004
ISO 11904-1:2002(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
The main task of technical committees is to prepare International Standards. Draft International Standards adopted
by the technical committees are circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 11904-1 was prepared by Technical Committee ISO/TC 43, Acoustics.
ISO 11904 consists of the following parts, under the general title Acoustics — Determination of sound immission
from sound sources placed close to the ear:
 Part 1: Technique using a microphone in a real ear (MIRE technique)
 Part 2: Technique using a manikin (manikin technique)
Annexes A and B of this part of ISO 11904 are for information only.
iv © ISO 2002 – All rights reserved

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SIST EN ISO 11904-1:2004
ISO 11904-1:2002(E)
Introduction
ISO 11904 is a series of standards which specify methods for the determination of sound immissions from sources
located close to the ear, in which situations the sound pressure level measured at the position of the exposed
person (but with the person absent) does not adequately represent the sound exposure.
In order to make it possible to assess the exposure by means of well established criteria, the exposure of the ear is
measured and subsequently converted into a corresponding free-field or diffuse-field level. The result is given as
free-field related or diffuse-field related equivalent continuous A-weighted sound pressure level, L or
,
FF H,Aeq
L when ISO 11904-1 is used, or L or L when ISO 11904-2 is used.
DF,H,Aeq FF,M,Aeq DF,M,Aeq
ISO 11904-1 describes measurements carried out using miniature or probe microphones inserted in the ears of
human subjects (microphone in real ear, MIRE technique). ISO 11904-2 describes measurements carried out using
a manikin equipped with ear simulators including microphones (manikin technique).
ISO 11904 may, for instance, be applied to equipment tests and the determination of noise exposure at the
workplace where, in the case of exposure from sources close to the ears, the sound pressure level measured at
the position of the exposed person (but with the person absent) does not adequately represent the sound
exposure. Examples of applications are head- and earphones used to reproduce music or speech, whether at the
workplace or during leisure, nailguns used close to the head, and combined exposure from a close-to-ear sound
source and an external sound field.
When specific types of equipment are to be tested (e.g. portable cassette players or hearing protectors provided
with radio receivers), test signals suitable for this particular type of equipment have to be used. Neither such test
signals nor the operating conditions of the equipment are included in ISO 11904 but might be specified in other
standards.
When workplace situations are measured, the various noise sources contributing to the immission should be
identified. Operating conditions for machinery and equipment used might be specified in other standards.
Both parts of ISO 11904 strive for the same result: a mean value for a population of the free-field or the diffuse-field
related level. ISO 11904-1 does this by specifying the mean of measurements on a number of human subjects;
ISO 11904-2 does this by using a manikin, which aims at reproducing the acoustical effects of an average human
adult. However, the two methods yield different measurement uncertainties which can influence the choice of
method. Only the method described in ISO 11904-1 gives results which indicate the variance in a human
population. Information on the uncertainties is given in annexes A and B.
When using the MIRE technique for measurement of sound from earphones of insert and stethoscopic types,
practical problems can occur with the positioning of microphones in the ear canal. When using the manikin
technique, the head- or earphone has to be coupled to the pinna simulator and ear canal extension as far as
possible in the way it is coupled to the human ear. In cases where head- or earphones or other objects touch the
pinna, a possible deviation in stiffness or shape of the artificial pinna from human pinnae has a significant impact
on the result and can even make the results invalid.
An overview of the differences of the two parts of ISO 11904 is given in Table 0.1.
© ISO 2002 – All rights reserved v

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SIST EN ISO 11904-1:2004
ISO 11904-1:2002(E)
Table 0.1 — Overview of differences between MIRE and manikin techniques
Parameter ISO 11904-1 ISO 11904-2
Type of method Microphone in real ear technique Manikin technique
Limitation of the With earphones of insert and stethoscopic A proper coupling may not always be obtained
method type, practical problems can occur with if the artificial pinna deviates from human
positioning of microphones in the ear canal. pinnae in stiffness or shape.
In some cases the exposed person cannot be
replaced by a manikin, e.g. if the person has
to operate equipment.
Main issues — Number of subjects — Similarity of manikin to human subjects
affecting accuracy
When tabulated values are used for ∆L or — Calibration of manikin
FF,H
∆L :
DF,H
 calibration of ear canal microphone
 accuracy in positioning of microphones in
the ear canal
When individual values are used for ∆L or
FF,H
∆L :
DF,H
 quality of reference sound field
 stability of sensitivity and frequency
response as well as position of ear canal
microphone
Frequency range 20 Hz to 16 kHz 20 Hz to 10 kHz


vi © ISO 2002 – All rights reserved

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SIST EN ISO 11904-1:2004
INTERNATIONAL STANDARD ISO 11904-1:2002(E)

Acoustics — Determination of sound immission from sound
sources placed close to the ear —
Part 1:
Technique using a microphone in a real ear (MIRE technique)
1 Scope
This part of ISO 11904 specifies basic framework measurement methods for sound immission from sound sources
placed close to the ear. These measurements are carried out with miniature or probe microphones inserted in the
ear canals of human subjects. The measured values are subsequently converted into corresponding free-field or
diffuse-field levels. The results are given as free-field related or diffuse-field related equivalent continuous
A-weighted sound pressure levels. The technique is denoted the microphone-in-real-ear technique (MIRE
technique).
This part of ISO 11904 is applicable to exposure from sources close to the ear, for example during equipment tests
or at the workplace by earphones or hearing protectors with audio communication facilities.
This part of ISO 11904 is applicable in the frequency range from 20 Hz to 16 000 Hz.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this part of ISO 11904. For dated references, subsequent amendments to, or revisions of, any of these publications
do not apply. However, parties to agreements based on this part of ISO 11904 are encouraged to investigate the
possibility of applying the most recent editions of the normative documents indicated below. For undated
references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain
registers of currently valid International Standards.
ISO 8253-2:1992, Acoustics — Audiometric test methods — Part 2: Sound field audiometry with pure tone and
narrow-band test signals
IEC 60065, Audio, video and similar electronic apparatus — Safety requirements
IEC 60268-7:1996, Sound system equipment — Part 7: Headphones and earphones
IEC 60601-1, Medical electrical equipment — Part 1: General requirements for safety
IEC 60942, Electroacoustics — Sound calibrators
IEC 61094-1, Measurement microphones — Part 1: Specifications for laboratory standard microphones
IEC 61260, Electroacoustics — Octave-band and fractional-octave-band filters
IEC 61672-1, Electroacoustics — Sound level meters — Part 1: Specifications
1)
GUM:1993 , Guide to the expression of uncertainty in measurement. BIPM, IEC, IFCC, ISO, IUPAC, IUPAP, OILM

1) Corrected and reprinted in 1995.
© ISO 2002 – All rights reserved 1

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SIST EN ISO 11904-1:2004
ISO 11904-1:2002(E)
3 Terms and definitions
For the purposes of this part of ISO 11904, the following terms and definitions apply.
3.1
ear canal measurement position
position in the ear canal where the sound pressure is measured
3.2
ear canal sound pressure level
L
ear
equivalent continuous sound pressure level measured at the ear canal measurement position
NOTE When measured during exposure to sound under test, it is denoted L . When optionally measured during
ear,exp
exposure to a reference sound field in the determination of the free-field or diffuse-field frequency response according to
clause 10, it is denoted L or L , respectively. When measured in one-third-octave frequency bands with nominal
,
ear FF ear,DF
midband frequency f these are denoted L , L and L .
ear,exp,f ear,FF,f ear,DF,f
3.3
human free-field frequency response
∆L
FF,H,f
difference, as a function of one-third-octave frequency bands f, between
 the sound pressure level at the ear canal measurement position with the subject exposed to a frontally incident
plane sound wave, and
 the sound pressure level of the same sound field with the subject absent
NOTE 1 The free-field frequency response is identical to the amplitude of the head-related transfer function (HRTF) for
frontal sound incidence.
NOTE 2 This definition is applicable to individual subjects and groups of subjects.
3.4
human diffuse-field frequency response
∆L
DF,H,f
difference, as a function of one-third-octave-frequency bands f, between
 the sound pressure level at the ear canal measurement position with the subject exposed to a diffuse sound
field, and
 the sound pressure level of the same sound field with the subject absent
NOTE This definition is applicable to individual subjects and groups of subjects.
3.5
free-field related sound pressure level
L
FF,H
sound pressure level of a plane sound wave which will give rise to the measured ear canal sound pressure level
L when the test subject is exposed to a frontally incident plane sound wave
ear,exp
NOTE The definition may be applied to specific frequencies or frequency bands, weighted or unweighted levels, specific
time weightings etc., for instance “free-field related equivalent continuous A-weighted sound pressure level” (free-field related
L , further abbreviated L ).
H,Aeq FF,H,Aeq
2 © ISO 2002 – All rights reserved

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SIST EN ISO 11904-1:2004
ISO 11904-1:2002(E)
3.6
diffuse-field related sound pressure level
L
DF,H
sound pressure level of a diffuse sound field which will give rise to the measured ear canal sound pressure level,
L , when the test subject is exposed to a diffuse field
ear,exp
NOTE The definition may be applied to specific frequencies or frequency bands, weighted or unweighted levels, specific
time weightings etc., for instance “diffuse-field related equivalent continuous A-weighted sound pressure level” (diffuse-field
related L , abbreviated to L ).
H,Aeq DF,H,Aeq
3.7
open ear canal
ear canal in which possible foreign objects (such as microphone, supporting elements and electrical leads) occupy
2
less than 5 mm of the cross-sectional area at any position along the ear canal
3.8
blocked ear canal
ear canal in which a foreign body (for instance an earplug) occupies the total cross-sectional area at some position
along the ear canal
3.9
partly blocked ear canal
ear canal which is neither fully open nor blocked
4 Measurement principle
Miniature microphones or probe microphones are placed to measure the sound pressure at a position in the ear
canal, denoted as the ear canal measurement position. The subject is exposed to the sound source(s) in question,
and the ear canal equivalent continuous sound pressure level is measured in one-third-octave frequency bands,
L .
ear,exp,f
Each of the one-third-octave band levels is adjusted with the free-field or diffuse-field frequency response, ∆L
FF,H,f
or ∆L , to obtain corresponding free-field related or diffuse-field related one-third-octave band sound pressure
DF,H,f
levels. These one-third-octave band levels are adjusted using A-weighting constants, and subsequently combined
to obtain the free-field related or diffuse-field related equivalent continuous A-weighted sound pressure level,
L or L .
FF,H,Aeq DF,H,Aeq
The measurements may be carried out for one or both ears as appropriate. The free-field or diffuse-field frequency
response is taken from clause 9, or determined for each individual subject and ear as described in clause 10.
NOTE The accuracy of the final result depends on a number of parameters (e.g. ear canal measurement position, number
of subjects, and whether clause 9 or 10 is used).
5 Instrumentation
5.1 Ear canal microphone
The sound pressure in the ear canal shall be measured by a microphone, which is either
 a miniature microphone placed in the ear canal, or
 a probe microphone consisting of a microphone placed outside the ear and equipped with a probe tube placed
in the ear canal; to prevent damage to the ear drum and the skin of the ear canal, the tube shall be made of a
soft material.
© ISO 2002 – All rights reserved 3

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SIST EN ISO 11904-1:2004
ISO 11904-1:2002(E)
The pressure response of the miniature or the probe microphone shall be without pronounced resonances, and it
shall be known except for the situation described in 10.9. The response shall be checked by comparison with a
calibrated pressure-type microphone which is in accordance with IEC 61094-1.
In the area of the concha, the microphone (including supporting elements and electrical leads) shall occupy an area
2
not exceeding 10 mm in any plane.
5.2 Reference field microphone
When individual free-field or diffuse-field frequency responses (∆L or ∆L ) are determined as described in
FF,H DF,H
clause 10, a reference field microphone is used to determine the sound pressure level in the reference sound field
with the subject absent. This microphone and the connected equipment used shall fulfil the requirements of
IEC 61672-1 for a class 1 instrument, and shall have a known free-field or diffuse-field frequency response.
5.3 Check of calibration
The calibration of the microphones and the measuring equipment shall be suitably checked. For the reference field
microphone, this shall be done using an acoustic calibrator complying with the requirements for class 1 of
IEC 60942.
5.4 Filters
Signals shall be analysed with one-third-octave band filters complying with the requirements for class 1 of
IEC 61260.
6 Subjects
Only persons free from inflammation and any other disease of the outer ear and the middle ear are suitable
subjects. For measurements in the open ear canal, only persons whose ear canals are not too narrow, flat or
severely bent, and who reveal no eardrum defects shall be chosen. If cerumen obstructs the ear canals, it shall be
removed. All such required actions shall be carr
...