Microphones and earphones for speech communications

Applies to the microphone part and earphone part of handsets, headsets or earsets for speech communications, and also to the microphone units and earphone units of built-in handsets, headsets or earsets. Establishes definitions relating to these electroacoustic transducers, standardizes the characteristics to be specified and the relevant methods of measurement.

Mikrofone und Kopfhörer für Sprachkommunikation

Microphones et écouteurs pour communications vocales

Applies to the microphone part and earphone part of handsets, headsets or earsets for speech communications, and also to the microphone units and earphone units of built-in handsets, headsets or earsets. Establishes definitions relating to these electroacoustic transducers, standardizes the characteristics to be specified and the relevant methods of measurement.

Microphones and earphones for speech communications (IEC 61842:2002)

General Information

Status
Published
Publication Date
30-Nov-2003
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
01-Dec-2003
Due Date
01-Dec-2003
Completion Date
01-Dec-2003

Buy Standard

Standard
SIST EN 61842:2003
English language
32 pages
sale 10% off
Preview
sale 10% off
Preview
e-Library read for
1 day

Standards Content (Sample)

SLOVENSKI SIST EN 61842:2003
STANDARD
december 2003
Microphones and earphones for speech communications (IEC 61842:2002)
ICS 17.140.50; 33.160.50 Referenčna številka
SIST EN 61842:2003(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 61842
NORME EUROPÉENNE
EUROPÄISCHE NORM June 2002
ICS 33.160.50; 17.140.50
English version
Microphones and earphones for speech communications
(IEC 61842:2002)
Microphones et écouteurs Mikrofone und Kopfhörer
pour communications vocales für Sprachkommunikation
(CEI 61842:2002) (IEC 61842:2002)

This European Standard was approved by CENELEC on 2002-05-01. 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, Czech Republic,

Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands,

Norway, Portugal, 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

© 2002 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 61842:2002 E
---------------------- Page: 2 ----------------------
EN 61842:2002 - 2 -
Foreword

The text of document 100/450/FDIS, future edition 1 of IEC 61842, prepared by IEC TC 100, Audio,

video and multimedia systems and equipment, was submitted to the IEC-CENELEC parallel vote and

was approved by CENELEC as EN 61842 on 2002-05-01.
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) 2003-02-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2005-05-01
Annexes designated "normative" are part of the body of the standard.
Annexes designated "informative" are given for information only.
In this standard, annex ZA is normative and annexes A and B are informative.
Annex ZA has been added by CENELEC.
__________
Endorsement notice

The text of the International Standard IEC 61842:2002 was approved by CENELEC as a European

Standard without any modification.

In the official version, for Bibliography, the following note has to be added for the standard indicated:

IEC 60268-2 NOTE Harmonized as HD 483.2 S2:1993 (not modified).
__________
---------------------- Page: 3 ----------------------
- 3 - EN 61842:2002
Annex ZA
(normative)
Normative references to international publications
with their corresponding 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 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 60268-1 1985 Sound system equipment HD 483.1 S2 1989
Part 1: General
2) 3)
IEC 60268-4 - Part 4: Microphones EN 60268-4 1999
2) 3)
IEC 60268-7 - Part 7: Headphones and earphones EN 60268-7 1996
2) 3)
IEC 60318-1 - Electroacoustics - Simulators of human EN 60318-1 1998
head and ear
Part 1: Ear simulator for the calibration
of supra-aural earphones
IEC 60603-11 1992 Connectors for frequencies below --
3 MHz for use with printed boards
Part 11: Detail specification for
concentric connectors (dimensions for
free connectors and fixed connectors)
2) 3)
IEC 60711 - Occluded-ear simulator for the HD 443 S1 1983
measurement of earphones coupled to
the ear by ear inserts
2) 3)
IEC 61094-1 - Measurement microphones EN 61094-1 2000
Part 1: Specifications for laboratory
standard microphones
2) 3)
IEC 61094-4 - Part 4: Specifications for working EN 61094-4 1995
standard microphones
ITU-T - Artificial mouth - -
Recommendation
P.51
HD 483.1 S2 includes A1:1988 to IEC 60268-1.
Undated reference.
Valid edition at date of issue.
---------------------- Page: 4 ----------------------
EN 61842:2002 - 4 -
Publication Year Title EN/HD Year
ITU-T - Coupling hearing aids to telophone sets - -
Recommendation
P.370
---------------------- Page: 5 ----------------------
INTERNATIONAL IEC
STANDARD
61842
First edition
2002-03
Microphones and earphones
for speech communications
 IEC 2002  Copyright - all rights reserved

No part of this publication may be reproduced or utilized in any form or by any means, electronic or

mechanical, including photocopying and microfilm, without permission in writing from 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

PRICE CODE
Commission Electrotechnique Internationale
International Electrotechnical Commission
Международная Электротехническая Комиссия
For price, see current catalogue
---------------------- Page: 6 ----------------------
– 2 – 61842  IEC:2002(E)
CONTENTS

FOREWORD...........................................................................................................................3

1 Scope...............................................................................................................................4

2 Normative references .......................................................................................................4

3 Terms and definitions .......................................................................................................4

3.1 Classification...........................................................................................................4

3.2 Devices for measurement........................................................................................6

3.3 Characteristics and performance .............................................................................6

4 Characteristics and measuring procedures .......................................................................7

4.1 General conditions ..................................................................................................7

4.2 Rated conditions .....................................................................................................8

4.3 Measuring conditions...............................................................................................9

4.4 Microphones for speech communications ..............................................................11

4.5 Earphones for speech communications .................................................................13

5 Connectors and contact designation ...............................................................................15

5.1 Miniature 4-position connector...............................................................................15

5.2 Concentric connector.............................................................................................15

6 Endurance of insulation ..................................................................................................15

7 Characteristics to be specified........................................................................................15

Annex A (informative) Miniature 4-position connector...........................................................25

Annex B (informative) Sub-miniature 2,5 mm concentric connector with three contacts........27

Bibliography..........................................................................................................................28

Figure 1 – Artificial ear for ordinary earphones .....................................................................18

Figure 2 – Example of the case for microphone unit measurement........................................18

Figure 3 – Example of the case for earphone unit measurement ...........................................19

Figure 4 – Determination of the artificial mouth position from the earcap reference point ......20

Figure 5 – Calibration system diagram for output sound pressure from artificial mouth..........20

Figure 6 – Measuring system diagram for microphone unit sensitivity ...................................21

Figure 7 – Diagram of listening test for normal operation of microphone ...............................22

Figure 8 – Measuring system diagram for earphone sensitivity..............................................23

Figure 9 – Diagram of listening test for normal operation of earphone...................................24

Figure 10 – Connection designation for plug of miniature 4-position connector .....................24

Figure A.1 – Shape and basic dimensions of plug for miniature 4-position connector ............25

Figure A.2 – Shape of plug interface part of jack for miniature 4-position connector..............26

Figure B.1 – 2,5 mm pin concentric connector (plug) with three contacts (tip, ring and

sleeve)..................................................................................................................................27

Table 1 – Definitions of earphone, headphone, earset and headset ......................................16

Table 2 – Characteristics of microphones for speech communication to be specified

and classification ..................................................................................................................16

Table 3 – Characteristics of earphones for speech communication to be specified

and classification ..................................................................................................................17

---------------------- Page: 7 ----------------------
61842  IEC:2002(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MICROPHONES AND EARPHONES FOR SPEECH COMMUNICATIONS
FOREWORD

1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of the 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, the IEC publishes International Standards. 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. The 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 the 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 National Committees.

3) The documents produced have the form of recommendations for international use and are published in the form

of standards, technical specifications, technical reports or guides and they are accepted by the National

Committees in that sense.

4) In order to promote international unification, IEC National Committees undertake to apply IEC International

Standards transparently to the maximum extent possible in their national and regional standards. Any

divergence between the IEC Standard and the corresponding national or regional standard shall be clearly

indicated in the latter.

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

equipment declared to be in conformity with one of its standards.

6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject

of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 61842 has been prepared by IEC technical committee 100: Audio,

video and multimedia systems and equipment.
The text of this standard is based on the following documents:
FDIS Report on voting
100/450/FDIS 100/479/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.

The committee has decided that the contents of this publication will remain unchanged until 2005.

At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
---------------------- Page: 8 ----------------------
– 4 – 61842  IEC:2002(E)
MICROPHONES AND EARPHONES FOR SPEECH COMMUNICATIONS
1 Scope

This standard applies to the microphone part and earphone part of handsets, headsets or

earsets for speech communications, and also to the microphone units and earphone units of

built-in handsets, headsets or earsets. The object of this standard is to establish definitions

relating to these electroacoustic transducers, and to standardize the characteristics to be

specified and the relevant methods of measurement. This does not exclude the use of other

methods of measurement which can be shown to give the same or more reliable results.

2 Normative references

The following reference 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 60268-1:1985, Sound system equipment – Part 1: General
IEC 60268-4, Sound system equipment – Part 4: Microphones
IEC 60268-7, Sound system equipment – Part 7: Headphones and earphones

IEC 60318-1, Electroacoustics – Simulators of human head and ear – Part 1: Ear simulator for

the calibration of supra-aural earphones

IEC 60603-11:1992, Connectors for frequencies below 3 MHz for use with printed boards –

Part 11: Detail specification for concentric connectors (dimensions for free connectors and

fixed connectors)

IEC 60711, Occluded-ear simulator for the measurement of earphones coupled to the ear

by ear inserts

IEC 61094-1, Measurement microphones – Part 1: Specifications for laboratory standard

microphones

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

microphones
ITU-T P.51, Artificial mouth
ITU-T P.370, Coupling hearing aids to telephone sets
3 Terms and definitions

For the purposes of this International Standard, the following terms and definitions apply.

3.1 Classification
3.1.1
handset

assembly for speech communications, which is a handle including a microphone part and an

earphone part suitable to be held by the talker's hand
---------------------- Page: 9 ----------------------
61842  IEC:2002(E) – 5 –
3.1.2
headset

assembly for speech communications, which consists of a holder to put on the talker's head,

one or two earphone parts and a microphone part, so as to keep the talker’s hands free

3.1.3
earset

assembly for speech communications, which consists of an earphone part and a microphone

part, so as to keep the talker’s hands free, without a holder to put on the talker's head

NOTE The distinction between an earset and a headset is as complicated as it is between an earphone and

a headphone. Table 1 explains the definitions of earphone, headphone, earset and headset used in this standard.

3.1.4
microphone for speech communications:

a) part of a handset, an earset or a headset, which functions as a microphone (an acousto-

electrical transducer)

b) assembly of a microphone unit for speech communications and a case for measurement

purposes, including acoustical circuit elements so as to obtain practical frequency

characteristics

NOTE 1 A microphone for speech communications is understood to include devices, if any, such as amplifiers or

impedance matching transformers up to the output terminals.

NOTE 2 A microphone for speech communications is called merely "microphone", or “microphone part” of a

handset, of an earset or of a headset, in Clause 4 of this standard and beyond.
3.1.5
earphone for speech communications

a) part of a handset, an earset or a headset, which functions as an earphone (an electro-

acoustic transducer)

b) assembly of an earphone unit for speech communications and a case for measurement

purposes, including acoustical circuit elements so as to obtain practical frequency

characteristics

NOTE 1 Any component which is intended by the manufacturer as an integral part of the earphone is included

during measurements.

NOTE 2 An earphone for speech communications is called merely "earphone", or “earphone part” of a handset, of

an earset or of a headset, in Clause 4 of this standard and beyond.
3.1.6
microphone unit for speech communications

acousto-electrical transducer installed in a handset, in an earset or in a headset to pick up the

talker's speech in the vicinity of his/her mouth

NOTE The microphone unit for speech communications is called merely a "microphone unit" in Clause 4 of this

standard and beyond.
3.1.7
earphone unit for speech communications

electroacoustic transducer installed in a handset, in an earset or in a headset to radiate sound

signal in the vicinity of the listener's ear

NOTE The earphone unit for speech communications is called merely an "earphone unit" in Clause 4 of this

standard and beyond.
3.1.8
case for unit measurement

case in which a microphone unit or an earphone unit for speech communications is installed

for measurement. It includes additional acoustic circuit elements so as to obtain practical

frequency characteristics, if necessary
---------------------- Page: 10 ----------------------
– 6 – 61842  IEC:2002(E)
3.2 Devices for measurement
3.2.1
mouthpiece holes

holes bored into the front of the enclosure of a microphone unit for speech communications,

to receive the input sound
3.2.2
earcap holes

holes bored into the front of the enclosure of an earphone for speech communications, to

radiate the output sound
3.2.3
artificial mouth

sound source for microphone measurement, which can produce the sound field similar to that

around an ordinary human mouth
3.2.4
artificial ear

acoustic load for earphone measurement, whose acoustic impedance is similar to that of an

ordinary human ear. It includes a microphone for measurement
3.2.5
lip ring

circular ring placed in front of the sound outlet of an artificial mouth for localizing the

equivalent lip position
3.2.6
lip plane

outer plane of the lip ring, giving the reference point for finding the measuring position

3.2.7
external d.c. power supply

d.c. power supply for a microphone for speech communications including an amplifier or an

electrical impedance converter circuit
3.2.8
additional resistance

electrical resistance for the earphone for speech communications which requires an external

resistance for necessary adjustment of characteristics of the device
3.2.9
probe coil

coil for measurement of the external magnetic field of an earphone for speech communications

3.3 Characteristics and performance
3.3.1
sensitivity (V/Pa)

absolute value of the ratio between the open-circuit output voltage from a microphone for

speech communications placed at a specified point in the sound field produced by the artificial

mouth and the sound pressure in the undisturbed free field at a specified calibration point, the

signal frequency being the reference frequency

NOTE Though the specified point for the microphone and the sound pressure calibration point should be identical

in general, these points may be different according to this Standard.
---------------------- Page: 11 ----------------------
61842  IEC:2002(E) – 7 –
3.3.2
sensitivity level (dB)

twenty times the logarithm to base ten of the sensitivity divided by the reference sensitivity

(1 V/Pa)
3.3.3
sensitivity to voltage (Pa/V)

absolute value of the ratio between the sound pressure produced by an earphone for speech

communications in the artificial ear and the voltage supplied to the earphone, the signal

frequency being the reference frequency
3.3.4
sensitivity level to voltage (dB)

twenty times the logarithm with a base of ten of the sensitivity divided by the reference

sensitivity (20 μPa/V)
3.3.5
sensitivity to power (Pa /W)

absolute value of the ratio between mean square of the sound pressure produced by an

earphone for speech communications in the artificial ear and the electrical power supplied to

the earphone, the signal frequency being the reference frequency
3.3.6
sensitivity level to power (dB)

ten times the logarithm with a base of ten of the sensitivity to power divided by the reference

−10 2
sensitivity (4 × 10 Pa /W)
3.3.7
electrical impedance (Ω)

absolute value of the internal impedance measured at the output terminals of a microphone

for speech communications or the input terminals of an earphone for speech communications

NOTE The word “electrical” is added in this Standard to distinguish the electrical impedance from the acoustical

or the mechanical impedance.
3.3.8
capacitance (nF)

capacitance measured at the input terminal of the earphone for speech communications

NOTE The capacitance is relevant only to earphones including a piezoelectric transducer because an ordinary

piezoelectric microphone includes an amplifier.
3.3.9
plane of magnetic field strength measurement

a plane parallel to the earcap reference plane at a distance of 10 mm (see 4.2.7)

4 Characteristics and measuring procedures
4.1 General conditions
IEC 60268-1 applies for the following items:
1) Units and system for measurement: IEC 60268-1, Clause 2.
2) Climatic conditions: IEC 60268-1, Clause 8.
3) Graphical presentation of data: IEC 60268-1, Clause 10.
---------------------- Page: 12 ----------------------
– 8 – 61842  IEC:2002(E)
4.2 Rated conditions

In order to perform measurements correctly and reproducibly, certain basic data, to be

specified by manufacturer, are essential, and these are termed 'rated conditions'. For a full

explanation of rated conditions, see IEC 60268-2.
4.2.1 Rated d.c. power supply voltage (V)
The d.c. power supply voltage for the microphone for speech communications.
4.2.2 Rated sinusoidal voltage (V)

The sinusoidal input voltage over the specified frequency range, under which the earphone for

speech communications can operate in a linear mode continuously without any thermal or

mechanical damage for a long time.
4.2.3 Rated sinusoidal power (W)
Electric power given by,
(U ) /Z
s r
where
U is the rated sinusoidal voltage;
Z is the rated impedance.
4.2.4 Rated noise voltage (V)

The pink noise input voltage over the specified frequency range, under which the earphone

for speech communications can operate in a linear mode continuously without permanent

damage for a long time.
4.2.5 Rated noise power (W)
Electric power given by,
(U ) /Z
n r
where
U is the rated noise voltage;
Z is the rated impedance.
4.2.6 Rated frequency range

Frequency range of a continuous input signal for a normal operation of a microphone or an

earphone for speech communications.
4.2.7 Earcap reference plane

Plane formed by the contacting points of a flat surface against the earcap of a handset, an

earset or a headset, or by the front plane of the case for earphone unit measurement.

NOTE Partly similar to the definition in ITU-T P.10 (see Bibliography).
4.2.8 Earcap reference point
Point in the earcap reference plane, used as a reference parameter.
NOTE See the note to 4.2.7.
---------------------- Page: 13 ----------------------
61842  IEC:2002(E) – 9 –
4.2.9 Rated impedance (Ω)

Absolute value of the electrical impedance of a microphone or earphone for speech

communications.

For an earphone with an electrodynamic transducer, it is recommended that the value is

chosen so that the lowest value of the modulus of the actual impedance within the rated

frequency range is not less than 80 % of the chosen value. Alternatively, it may be given as

the value at the reference frequency or the value at the frequency specified by the

manufacturer.
4.2.10 Rated capacitance (nF)

The capacitance of an earphone for speech communications at the frequency specified by the

manufacturer, or at 120 Hz, if not specified.
4.3 Measuring conditions
4.3.1 Environmental interference

The level of disturbances due to environmental noise, reverberation, wind noise, electro-

magnetically induced noise, vibration noise and other interference shall be at least 10 dB

below the measured quantity.
4.3.2 Reference sound pressure

The reference sound pressure for a microphone shall be 1 Pa and that for an earphone shall

be 20 μPa.
4.3.3 Signal for measurement
A sinusoidal signal shall be used for measurement unless otherwise specified.

Results may also be gained from measurements using noise signals, quasi-random sequence

signals or impulsive signals. If signals other than sinusoidal signals are used, it is the

responsibility of the test house to show that the results are equivalent or have fewer artefacts

than those obtained with sinusoidal signals.
4.3.4 Reference frequency and frequency range

The reference frequency shall be 1 kHz. The frequency range shall be from 150 Hz to 5 kHz

unless otherwise specified. The frequency values for measurement at discrete frequency

points shall be specified by the manufacturer.
4.3.5 Apparatus for acoustic measurement
The following apparatus shall be used.
a) Microphone for measurement

A condenser microphone conforming to IEC 61094-1 or IEC 61094-4 shall be used. Type

LS2P or equivalent, or smaller than LS2P, is recommended. A pressure microphone
whose sensitivity was calibrated by using the standard condenser microphone is
acceptable.
b) Artificial mouth
The artificial mouth defined by ITU-T Recommendation P.51 shall be used.
c) Artificial ear

The artificial ear defined in IEC 60318-1 or IEC 60711 shall be used. Additional components

shall be used, if necessary.
---------------------- Page: 14 ----------------------
– 10 – 61842  IEC:2002(E)

The type of artificial ear to be used, and conditions relating to shape, dimension or other

characteristics of the additional components shall be specified by the manufacturer. In

particular, the following items shall be specified clearly.
1) Position of the earcap reference plane,
2) Position of the earcap reference point, and,
3) Direction of axis of the microphone part.

The artificial ear specified in IEC 60318-1, or an artificial ear with a construction as shown in

Figure 1, is recommended for measurement of the supra-aural earphone, defined in the

Clause 1 of IEC 60268-7: with minimized leakage, mainly for measurements at less than

3.4 kHz.

NOTE 1 The positions of the earcap reference plane and the earcap reference point may be different for a

different handset, headset or earset to be measured, even if the same artificial ear is used.

NOTE 2 Only the P type microphone is suitable for use in the artificial ear.

NOTE 3 Recent developments in ITU-T describe the use of head and torso simulator (HATS) for the measurement

of communication devices. The relevant Recommendations are ITU-T P.58, ITU-T P.57 and ITU-T P.64. A measurement

equipment according to these recommendations can be used alternatively. The chosen test configuration shall be

described unambiguously in the test report as well as the exact positioning of the device under test.

4.3.6 Apparatus for electrical measurement
The following instruments shall be used.
a) Automatic frequency response recorder

Interruption of the signal frequency trace at any instant during the measurement shall

affect the indicated response by less than 1 dB.
b) Sinusoidal signal generator and amplifier

The amplifier associated with the sinusoidal signal generator shall conform to the following

requirements:

1) The total harmonic distortion of the signal applied to the artificial mouth for radiation of

the output sound pressure of 1 Pa under the calibration condition (see 4.3) shall be

less than 0,1 %.

2) Earphone to be measured, or the earphone with the necessary additional resistance,

shall be less than 0,1 %.

3) The output level across the rated pure resistance load of the amplifier shall not differ

by more than 1 dB from the output level across a load of ten times the rated
resistance.
4.3.7 Cases for unit measurement

The acoustical performance of a microphone or earphone unit is often strongly dependent on

the mechanical and acoustical properties of the housing in which it is to be operated.

Therefore, the microphone/earphone unit to be measured shall be installed in a case for unit

measurement unless otherwise specified. An example of a case for microphone unit
meas
...

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.