Sound system equipment - Part 7: Headphones and earphones

Applies to headphones and headsets intended to be used on the human ear. Standardizes the designation and description of headphones, and lists characteristics to be specified, with the relevant methods of measurement.

Elektroakustische Geräte - Teil 7: Kopfhörer und Ohrhörer

Equipements pour systèmes électroacoustiques - Partie 7: Casques et écouteurs

S'applique aux casques et casques microphoniques prévus pour être utilisés sur l'oreille humaine. Normalise la désignation et la description des écouteurs et énumère les caractéristiques à spécifier, ainsi que les méthodes de mesure correspondantes qui les concernent.

Sound system equipment -- Part 7: Headphones and earphones (IEC 60268-7:1996)

General Information

Status
Withdrawn
Publication Date
31-May-1996
Withdrawal Date
30-Nov-1996
Current Stage
9960 - Withdrawal effective - Withdrawal
Start Date
02-Jan-2014
Completion Date
02-Jan-2014

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SLOVENSKI STANDARD
SIST EN 60268-7:1999
01-april-1999
Sound system equipment -- Part 7: Headphones and earphones (IEC 60268-7:1996)
Sound system equipment -- Part 7: Headphones and earphones
Elektroakustische Geräte -- Teil 7: Kopfhörer und Ohrhörer
Equipements pour systèmes électroacoustiques -- Partie 7: Casques et écouteurs
Ta slovenski standard je istoveten z: EN 60268-7:1996
ICS:
33.160.50 Pribor Accessories
SIST EN 60268-7:1999 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 60268-7:1999
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SIST EN 60268-7:1999
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SIST EN 60268-7:1999
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SIST EN 60268-7:1999
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SIST EN 60268-7:1999
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SIST EN 60268-7:1999
CEI
NORME
IEC
INTERNATIONALE
268-7
INTERNATIONAL
Deuxième édition
STANDARD Second edition
1996-02
systèmes électroacoustiques -
Equipements pour
Partie 7:
Casques et écouteurs
Sound system equipment
Part 7:
Headphones and earphones
O CEI 1996 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

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

cédé, électronique ou mécanique, y compris la photocopie et including photocopying and microfilm, without permission

les microfilms, sans l'accord écrit de l'éditeur. in writing from the publisher.
Genève, Suisse

Bureau Central de la Commission Electrotechnique Internationale 3, rue de Varembé

Commission Electrotechnique Internationale CODE PRIX
I EC
International Electrotechnical Commission
PRICE CODE
MetHnyHapoAHae 3neKTporeXHH4ecitaa IHOMHCCHH
voir catalogue en vigueur
Pour prix, •
For price, see current catalogue
---------------------- Page: 7 ----------------------
SIST EN 60268-7:1999
268-7 © IEC:1996 - 3 -
CONTENTS
Page
5
FOREWORD
Clause
1 General 7
1.1 Scope 7
7
1.2 Normative references
11
1.3 Definitions
13 1.4 Classification, designation and coding
21
Marking of terminals, controls and polarity
1.5
21 1.6 User instructions
21 Conditions for specifications and measurements
21
Rated conditions 2.1
23 2.2 Standard conditions for measurement
25
2.3 Couplers and ear simulators
25
2.4 Loudness comparison conditions
27 2.5 Ear canal sound pressure level measurement conditions
27 3 Characteristics to be specified and their methods of measurement
27
3.1 Power supply
27 3.2 Electrical impedance
3.3 Input voltage 29
35 3.4 Input power
35 3.5 Sound pressure (level)
37 3.6 Frequency response
45 3.7 Amplitude non-linearity
49 Rated climatic conditions (these are rated conditions)
3.8
51 3.9 External magnetic field
51 3.10 Unwanted sound radiation
51
3.11 Sound attenuation
53
3.12 Crosstalk attenuation for multi-channel headphones
53
3.13 Application force (this is a rated condition)
53 3.14 Physical characteristics, cables and connectors
55
4 Classification of characteristics
Annexes
57

A Specification and conditions of use of a microphone for use inside the ear canal

59
Practical details of free-field comparison conditions
61 Practical details of diffuse-field comparison conditions

Practical details of the subjective comparison and ear canal sound pressure level

63
conditions
65
Bibliography E
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SIST EN 60268-7:1999
268-7 © IEC:1996 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
SOUND SYSTEM EQUIPMENT -
Part 7: Headphones and earphones
FOREWORD

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

International Standard IEC 268-7 has been prepared by IEC technical committee 84:

Equipment and systems in the field of audio, video and audiovisual engineering.

This second edition cancels and replaces the first edition published in 1984, and consti-

tutes a technical revision.
The text of this standard is based on the following documents:
FDIS Report on voting
84/417/FDIS 1000/4/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.
Annex A forms an integral part of this standard.
Annexes B, C, D and E are for information only.
---------------------- Page: 9 ----------------------
SIST EN 60268-7:1999
-7 -
268-7 © IEC:1996
SOUND SYSTEM EQUIPMENT -
Part 7: Headphones and earphones
1 General
1.1 Scope

This part of IEC 268 applies to headphones, headsets, earphones and earsets, intended to

be used on, or in, the human ear. It also applies to equipment, such as pre-amplifiers,

passive networks and power supplies which form an integral part of the headphone
system.
It does not deal with:

- safety, for which reference should be made to IEC 65 [1]* or another appropriate

standard;

- the characteristics of microphones of headsets, for which reference should be made

to IEC 268-4 [2];

- earphones and other devices for hearing aids, for which reference should be made

to IEC 118-0 [3];
- headphones for audiometry;

- headphones and other devices which form pa rt of an active ear-defender system,

although some of its provisions may be applicable.

This standard specifies the characteristics which should be included by the manufacturer

in specifications, and relevant methods of measurement. It includes a classification of the

different types of earphone, mainly characterized by the way in which the transducer is

coupled acoustically to the ear, and a classification code which may also be used for

marking.
1.2 Normative references

The following normative documents contain provisions which, through reference in this

text, constitute provisions of this part of IEC 268. At the time of publication, the editions

indicated were valid. All normative documents are subject to revision, and pa ies to

agreements based on this pa rt of IEC 268 are encouraged to investigate the possibility of

applying the most recent editions of the normative documents indicated below. Members

of IEC and ISO maintain registers of currently valid International Standards.
IEC 38: 1983, IEC standard voltages

IEC 50(801): 1994, International Electrotechnical Vocabulary - Chapter 801: Acoustics

and electroacoustics
IEC 68: Basic environmental testing procedures
* Figures in square brackets refer to the bibliography given in annex E.
---------------------- Page: 10 ----------------------
SIST EN 60268-7:1999
- 9 -
268-7 © IEC:1996
IEC 86: Primary batteries
Guide for specifying environmental conditions for equipment
IEC Guide 106: 1989,
performance rating
Scales and sizes for plotting frequency characteristics and polar diagrams
IEC 263: 1982,
Sound system equipment - Part 1: General
IEC 268-1: 1985,
Sound system equipment - Part 2: Explanation of general terms and
IEC 268-2: 1987,
calculation methods
Sound system equipment - Part 3: Amplifiers
IEC 268-3: 1987,
Sound system equipment - Part 11: Applications of connectors for the
IEC 268-11: 1987,
interconnection of sound system components
Sound system equipment - Part 12: Applications of connectors for
IEC 268-12: 1987,
broadcast and similar use
Sound system equipment - Part 15: Preferred matching values for the
IEC 268-15: 1987,
interconnection of sound system components
Occluded-ear simulator for the measurement of earphones coupled to the
IEC 711: 1981,
ear by ear inserts
Conference systems - Electrical and audio requirements
IEC 914: 1988,
Provisional head and torso simulator for acoustic measurements on air
IEC 959: 1990,
conduction hearing aids
Acoustics - Determination of sound power levels of noise sources -
ISO 3741: 1988,
Precision methods for broad-band sources in reverberation rooms
Acoustics - Hearing protectors - Part 1: Subjective method for the
ISO 4869-1: 1990,
measurement of sound attenuation
Acoustics - Hearing protectors - Part 3: Simplified method for the
TR 4869-3: 1989,
ISO

measurement of insertion loss of ear-muff type protectors for quality inspection purposes

---------------------- Page: 11 ----------------------
SIST EN 60268-7:1999
268-7 ©IEC:1996 - 11 -
Definitions
1.3
of IEC 268, the following definitions apply:
For the purpose of this pa

NOTE — Any device included between a transducer as defined in 1.3.1 to 1.3.15 and the connector(s) for

electrical input should be regarded as part of the transducer.
Electroacoustic transducer by which acoustic oscillations are obtained from
earphone:
1.3.1

electric signals and intended to be closely coupled acoustically to the ear. [IEV 801-27-18]

Assembly of one or two earphones on a headband or chinband, the
headphone:
1.3.2
use of which may be optional (e.g. with intra-concha earphones).
Headphones equipped with a microphone.
1.3.3 headset:
Earphones equipped with a microphone.
1.3.4 earset:

NOTE — This definition is included because the term appears in the catalogue of IEC publications.

Small earphone that is attached directly to a connecting element,
insert earphone:
1.3.5
for example an earmould, inserted into the ear canal. [IEV 801-27-22, modified]
Small earphone that fits in the concha cavity, with its
intra-concha earphone:
1.3.6
acoustic exit close to the entrance of the ear canal.
earphone" is modified from that in IEC 50(801), and the definition of "intra-
NOTE — The definition of "inse

concha earphone" introduced, because the methods of measurement of the two types differ.

Earphone applied externally to the outer ear and intended
supra-aural earphone:
1.3.7
to rest on the pinna. [IEV 801-27-23, modified]
Earphone intended to rest on the ridges of the concha
1.3.8 supra-concha earphone:
cavity.
Earphone having a cavity large enough to cover the region
1.3.9 circumaural earphone:
of the head including the ear. [IEV 801-27-24]
1.3.10 ear shell: Circumaural type of earphone hanging on the ear. [IEC 914]
Insert headphone by which the earphone(s) is/are
1.3.11 stethoscopic headphone:

coupled to the ears by means of a pair of rigid tubes, so that the assembly resembles a

stethoscope.
Earphone which intentionally provides an acoustic
acoustically open earphone:
1.3.12
path between the external environment and the ear canal.
Earphone which is intended to prevent acoustic
acoustically closed earphone:
1.3.13
coupling between the external environment and the ear canal.
Earphone which does not emit significant sound radiation
1.3.14 closed-back earphone:
from the back of the transducer to the external environment.
Earphone which emits significant sound radiation from the
open-back earphone:
1.3.15
back of the transducer to the external environment.
---------------------- Page: 12 ----------------------
SIST EN 60268-7:1999
268-7 © IEC:1996 - 13 -
1.4 Classification, designation and coding
The following designations and classification codes shall be used:
268-7 - IEC - XXXX - NNRN - N
where:

268-7-IEC is the standard form of prefix (see 2.4.7 of lEC directives, part 3, [4]);

X (first letter) gives the principle of the transducer:
D - electrodynamic (moving coil);
E - electret (self-polarizing);
F - piezo-electric (polymer);
M - electromagnetic (moving armature or diaphragm);
P - piezo-electric (ceramic);
S - electrostatic (externally polarized);
- X (second letter) gives the type of earphone (see figure 1):
C - circumaural;
E - intra-concha;
H - earshell;
I - inse
rt ;
M - supra-concha;
S - supra-aural;
T - stethoscopic;

X (third letter) gives the intended nature of the acoustic coupling to the ear canai:

L - acoustically open;
S - acoustically closed;
X (fourth letter) gives the intended nature of the radiation to the external
environment:
C - closed-back (see 1.3.13);
O - open-back (see 1.3.14);

An illustration of the four possibilities defined in 1.3.12 to 1.3.15, and indicated by the third

and fourth classification letters, is given in figure 2;

- NNRN (first number) gives the impedance in ohms in "mantissa and exponent" form.

(For example, 8 S2 as "08R0", 32 S2 as "32R0" and 600 S2 as "06R2");
- N (second number) gives the number of channels.
The code, compiled in accordance with the above rules, may be used for marking.
---------------------- Page: 13 ----------------------
SIST EN 60268-7:1999
open earphone Ear loudspeaker
Type of earphone Acoustically closed earphone Acoustically
(minimum leakage) (controlled leakage)
HOUSING PROTECTOR PROTECTOR
PROTECTOR HOUSING HOUSING
Caudal
Caudal ; Caud al
.glii
/ } sta.
j j
Circumaural / back °/ "",/
/ / back / back
I// frontont
i/ front frontt
IIII:' Rostral Ih Rostral '''/ Rostral
EARPAD
EARPAD
TRANSDUCER
TRANSDUCER
TRANSDUCER
EARPAD
EARPAD
/ Caudal }
Caud
ÿ 1 back
-'^
Supra-aural
back /
^/,/,^
i^l I% front
front \ ^^i^
G 1,
Rostral
A Rostra
TRANSDUCER
HOUSING
HOUSING TRANSDUCER
EARPAD
PROTECTOR EARPAD PROTECTOR
Caudal
r„,, , Caudal
back
:'-^ 'I
Supra-concha
'^ I ^^ ^j' back I
J, front
front ^`,r
` ^^
.; j,,/A Rostral
/ Rostral
HOUSING TRANSDUCER
HOUSING TRANSDUCER

Figure 1 - Diagrammatic horizontal sections showing types of earphone and their spatial relationships with

the pinna and/or canal entrance
---------------------- Page: 14 ----------------------
SIST EN 60268-7:1999
Acoustically closed earphone Acoustically open earphone
Type of earphone
(minimum leakage) (controlled leakage)
EARPAD r
EARPAD
Caudal
Caudal
PROTECTOR;""
PROTECTOR"-4,,
I ntra-concha back
back
/ front
front
HOUSING ''j •/ 1^A HOUSING
TRANSDUCE-
TRANSDUCER
Rostra)
Rostra)
EARPAD
EARPAD
PROTECTOR
Caudal
Caudal
PROTECTOR
/ back ;
Insert back
All
'' front ',' front
HOUSING,
HOUSING 1
Rostra) Rostra)
TRANSDUCER
TRANSDUC:R
NOTE:
Cross hatching shows
.•. Insert with sound tube
EARPIECE •
EARPIECE `,
•,.,.„.„i acoustically closed
SOUNDTUBE ”% SOUNDTUBE #.'"
between transducer
earpad to accomplish
., minimum leakage
and earpiece (for =^,i1/ •:^ ..
Spotted by small circle
uli ^'
example, stethoscopic 1,,, ^'
::Kf: shows porous material
^^^^
i^^^
of earphone for
ttype
earpad to accomplish
e PROTECTOR PROTECTOR
controlled leakage
hearing aid) HOUSING
HOUSING
TRANSDUCER TRANSDUCER
Figure 1 (continued)
---------------------- Page: 15 ----------------------
SIST EN 60268-7:1999
Type of earphone Closed-back Open-back
(does not emit significant (emits significant sound
sound radiation from the radiation from the back of
back of the transducer to the the trandsducer to the
external environment)
external environment)
PROTECTOR
HOUSING PROTECTOR
HOUSING
Caudal
Caudal
Acoustically closed
(intended to prevent acoustic
back
back
-4-
coupling between the
front
front
external environment and
Rostra!
Rostra) ^
the ear canal)
EARPAD
EARPAD
TRANSDUCER
TRANSDUCER
HOUSING
Caudal Caudal
Acoustically open
(intentionally provides an
back back
acoustic path between the
front front
external environment and
Rostra)
Rostra)
the ear canal)
TRANSDUCE
EARPAD
PROTECTOR
Note: Arrows show sound flow or sound leakage

Figure 2 - Diagrams showing the four possible constructions: acoustically open or closed,

and closed- or open-back
---------------------- Page: 16 ----------------------
SIST EN 60268-7:1999
268-7 ©IEC:1996 - 21 -
1.5 Marking of terminals, controls and polarity

Requirements for marking terminals and controls are given in IEC 268-1, and for polarity

in IEC 268-2. In addition, headphones which are intended to be worn with a particular

earphone on each ear shall be marked to indicate the "left" and "right" earphones. If a

colour marking is used, the "right" earphone shall be indicated by a red marking.

1.6 User instructions
The user instructions shall include information on:
connector contact assignments (see IEC 268-11);
- controls and switches (if any);
- microphone (if any);
- diagram of the interconnections of the earphones (if more than one);
- classification code (see 1.4);
- description of the type of headphone.

Information shall also be provided on the safe use of the headphone, using wording

similar to:

"To prevent possible hearing damage, do not listen at high volume levels for long

periods. Do not use the headphones while driving or cycling or in any situation where

you should be able to hear other sounds. As a guide to setting the volume level, check

that you can still hear your own voice, when speaking normally while listening with the

headphones."

If the headphone is supplied with auxiliary equipment, information shall also be provided on:

- pre-amplifiers and/or passive networks;
- receivers (for cordless systems);
- power supplies;
other parts, such as magnetic pick-up devices.
2 Conditions for specifications and measurements
2.1 Rated conditions

For an explanation of the meaning of "rated conditions" and "rated value of a character-

istic", reference shall be made to IEC 268-2.
---------------------- Page: 17 ----------------------
SIST EN 60268-7:1999
268-7 © IEC:1996 –
23 –
The rated conditions for a headphone are:
rated impedance;
rated source e.m.f. (or power, see 3.4);
rated noise e.m.f. (or power, see 3.4);
rated source impedance (see note);
rated frequency range;
rated long-term maximum input voltage (or power);
rated maximum permanent noise source e.m.f. (or power);
rated power supply voltage (if any);
rated climatic conditions (temperature, humidity, air pressure);
rated damage limited source e.m.f.;
rated application force.

These values are taken from the manufacturer's specification, and are not subject to

measurement; they constitute the basis for measuring the other characteristics.

For climatic conditions, reference is made to IEC 268-1, and further information is given in

IEC 68 and IEC guide 106.

NOTE — The performance of most types of headphones depends very little on the source impedance.

However, in order to allow headphones of widely different impedances to be reasonably well-matched, in

terms of the sound pressure level produced, to a single headphone output on other equipment, IEC 268-15 at

present specifies a source impedance of 120 52, intermediate between the lowest and highest likely

impedances of available headphones. It is thus important for the manufacturer to specify the rated source

D..
impedance, particularly if, for some reason, it is not 120
2.2 Standard conditions for measurement

A headphone is working under standard conditions for measurement when all of the follow-

ing conditions are fulfilled:

a) At least one earphone is applied to the appropriate coupler or ear simulator, with

the rated application force.

b) A sinusoidal voltage at the standard measuring frequency is applied, in series with

the rated source impedance. The voltage shall be such that a sound pressure level

of 94 dB (ref 20 µPa) is generated in the coupler or ear simulator. Unless otherwise

stated, the standard measuring frequency shall be 500 Hz. The input signal shall be

applied at the point where the signal from an amplifier or other equipment is applied when

the headphone is in use. This point may be the input of a piece of auxiliary equipment,

such as a preamplifier.

As an alternative, the manufacturer may specify this condition as being a signal voltage

which dissipates a power of 1 mW in a pure resistance equal to the rated impedance of

the earphone being measured.

NOTE — Electrostatic, piezo-electric, electret and cordless headphones are within the scope of this

standard. The signal may be sent to the headphone by infra-red, radio, light or magnetic induction (either

directly to the transducers or to a magnetic pick-up device and amplifier). These types of headphone are

more easily dealt with by specifying the sound pressure level to be generated (the input signal being applied

to the transmitter unit), rather than by specifying the power in the rated impedance.

---------------------- Page: 18 ----------------------
SIST EN 60268-7:1999
268-7 © IEC:1996 - 25 -

c) Unless otherwise specified by the manufacturer, volume controls are set at minimum

attenuation. For headphones supplied with a preamplifier, and for cordless head-

phones, the manufacturer shall specify a reference position of the gain control for use

in measurements. Other controls shall be set at the designated "normal" positions, or at

stated positions, preferably those giving the greatest range of frequency response.

Balance controls shall be set for equal voltages at the terminals of the channels.

Crosstalk controls shall be set for minimum crosstalk.

d) If the headphone requires a power supply, the rated supply voltage and frequency

are applied.
2.3 Couplers and ear simulators

The manufacturer shall specify the type of coupler or ear simulator which was used to

determine the published specification of the headphone or earphone. If an artificial head,

or head and torso simulator (HATS), equipped with suitable ear simulators is used, this

shall be stated with the results.
2.4 Loudness comparison conditions

The response of a headphone to a given electrical signal may be determined by subjective

comparison of the loudness of the sound from the headphone with that of a reference

sound field derived from the same electrical signal. Headphones provided with earphones

for both ears shall be operated with uncorrelated signals, having the same spectrum and

amplitude, applied to both earphones simultaneously.
2.4.1 Free-field comparison conditions

A headphone is working under free-field comparison conditions when both of the following

conditions are fulfilled:
a) the headphone is worn by a test person in accordance with the manufacturer's

instructions or in the usual way for that type. It is necessary to fit the headphone in

accordance with the manufacturer's instructions, so that the earphones are correctly

positioned, and the application force is close to the rated value.

b) the reference sound field simulates a progressive plane wave. The acoustic signal

shall have a specified bandwidth and sound pressure level at a stated reference point,

in the absence of the test person.
Practical details of free-field comparison conditions are given in annex B.
2.4.2 Diffuse-field comparison conditions

A headphone is working under diffuse-field comparison conditions when both of the follow-

ing conditions are fulfilled:
a) the headphone is worn by a test person in accordance with the manufacturer's

instructions or in the usual way for that type. It is necessary to fit the headphone in

accordance with the manufacturer's instructions, so that the earphones are correctly

positioned, and the application force is close to the rated value;
---------------------- Page: 19 ----------------------
SIST EN 60268-7:1999
268-7 © IEC:1996 - 27 -

b) the reference sound field simulates a diffuse sound field, as described in ISO 3741.

The acoustic signal shall have a specified bandwidth and sound pressure level at a

stated reference point, in the absence of the test person.

Practical details of diffuse-field comparison conditions are given in annex C. The use of

a reverberant chamber for the generation of the diffuse field is suitable for ear canal

probe measurements, but less suitable for subjective loudness level comparison,
because of the long reverberation time.
2.5 Ear canal sound pressure level measurement conditions

A headphone is working under ear canal sound pressure level measurement conditions

when the conditions for free-field comparison (2.4.1) or diffuse-field comparison (2.4.2)

are fulfilled, in addition to the following condition.

A very small microphone, in accordance with the requirements in annex A, is positioned

inside the ear canal of the test person, with its sound entrance at least 4 mm from the

entrance of the canal.
Practical details of these conditions are given in annex D.
3 Characteristics to be specified and their methods of measurement
3.1 Power supply
If the headphone requires a power supply, the manufacturer shall specify:
- the type of power supply (a.c. or d.c.);

- the rated supply voltage and frequency, or their ranges (see IEC 38) and/or type of

battery (see IEC 86). These are rated conditions (see 2.1);
- the maximum power drawn from the power supply.

Headphones, which require or tolerate a small direct current in addition to the signal, are

not regarded as requiring a power supply. However, details of the required or maximum

permissible direct current shall be given.
3.2 Electrical impedance
3.2.1 Rated impedance (this is a rated condition: see 2.1)
3.2.1.1 Characteristic to be specified.

The value of a pure resistance which is specified by the manufacturer for matching

purposes. The rated impedance shall be 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 rated

value. If the impedance at any frequency between 0 kHz and 20 kHz is less than this

value, this should be stated in the specification.
3.2.2 Impedance/frequency characteristic
3.2.2.1 Characteristic to be specified
Representation of the modulus of the impedance as a function of frequency.
---------------------- Page: 20 ----------------------
SIST EN 60268-7:1999
268-7 © IEC:1996 - 29 -
3.2.2.2 Method of measurement
a) The headphone is brought under standard conditions for measurement.

b) The signal is changed to a sinusoidal voltage or current of variable frequency,

whose amplitude is constant, and sufficiently small to ensure that the headphone oper-

ates in a linear region.
c) The modulus of the impedance shall be measured, at least over the frequency
range 20 Hz to 20 kHz.

d) The results shall be presented graphically as a function of frequency. The value of

signal voltage or current shall be stated.
3.2.3 Rated source impedance (this is a rated condition)
3.2.3.1 Characteristic to be specified
The source impedance, specified by the manufacturer, with which the headphone is
intended to operate.
NOTE - See note to 2.1.
3.3 Input voltage
3.3.1 Rated source e.m.f. (this is a rated condition)
3.3.1.1 Characteristic to be specified

The maximum r.m.s. voltage (on peaks of programme signal), specified by the manu-

facturer, which should be applied to the headphone through the rated source impedance,

during the reproduction of normal programme signals.
NOTES

1 For headphones intended to comply with the matching requirements at present in IEC 268-15, the rated

source e.m.f. should be 5 V. See also 1.6 and the note to 2.1.

2 Attention is drawn to the need for discouraging the use of headphones at sound pressures that might

cause damage to hearing. The rated input voltage should, preferably, not exceed the characteristic voltage

(see 3.3.3) by more than 10 dB to 15 dB. See also note 2 to 3.3.4.1.
3.3.2 Limiting values of input voltage
3.3.2.1 Characteristics to be specified

The rated long-term maximum source e.m.f. (a rated condition) is the maximum voltage,

applied through the rated source impedance, which the headphone can tolerate without

permanent damage, when the signal is a noise signal simulating normal programme

material (see IEC 268-1), with additional clipping, and is applied for 10 periods of 60 s,

separated by periods of zero signal of 120 s duration.

The rated maximum permanent noise source e.m.f. (a rated condition) is the maximum

voltage, applied through the rated source impedance, which the headphone can tolerate

without permanent damage, when the signal is a noise signal simulating normal
with additional clipping, and is applied for a continuous
programme material (see IEC 268-1),
period of 100 h.
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SIST EN 60268-7:1999
– 31 –
268-7 © IEC:1996
3.3.2.2 Methods of measurement
NOTE — Since these are rated conditions, they are not,
...

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