EN 60268-7:1996

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

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
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268-7 © IEC:1996 - 3 -
CONTENTS
Page
FOREWORD
Clause
1 General 7
1.1 Scope 7
1.2 Normative references
1.3 Definitions
13 1.4 Classification, designation and coding
Marking of terminals, controls and polarity
1.5
21 1.6 User instructions
21 Conditions for specifications and measurements
Rated conditions 2.1
23 2.2 Standard conditions for measurement
2.3 Couplers and ear simulators
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
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
3.11 Sound attenuation
3.12 Crosstalk attenuation for multi-channel headphones
3.13 Application force (this is a rated condition)
53 3.14 Physical characteristics, cables and connectors
4 Classification of characteristics
Annexes
A Specification and conditions of use of a microphone for use inside the ear canal
Practical details of free-field comparison conditions
B
61 Practical details of diffuse-field comparison conditions
C
Practical details of the subjective comparison and ear canal sound pressure level
D
conditions
Bibliography E
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
1)
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.

-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
rt
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.

- 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

268-7 ©IEC:1996 - 11 -
Definitions
1.3
of IEC 268, the following definitions apply:
rt
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-
rt
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.

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.

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
I
A
IIII:' Rostral Ih Rostral '''/ Rostral
EARPAD
EARPAD
TRANSDUCER
TRANSDUCER
TRANSDUCER
EARPAD
EARPAD
al
/ Caudal }
Caud
ÿ 1 back
-'^
Supra-aural
back /
^/,/,^
7^
i^l I% front
.
front \ ^^i^
G 1,
Rostral
1f
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

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
j
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
p
earpad to accomplish
e PROTECTOR PROTECTOR
controlled leakage
hearing aid) HOUSING
HOUSING
TRANSDUCER TRANSDUCER
Figure 1 (continued)
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
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.

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.

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;

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.

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.
– 31 –
268-7 © IEC:1996
3.3.2.2 Methods of measurement
NOTE — Since these are rated conditions, they are not, strictly, subject to measurement, except by the
manufacturer. The following method is standardized to encourage all manufacturers to use the same method,
and it may be used by test houses for verification of manufacturers' specifications.
a) The following equipment is required:
a source of the weighted noise signal, which can be switched on and off for
–
specified short periods of time;
– a clipping network;
a power amplifier;
–
any auxiliary equipment which is normally connected between the amplifier and
–
the headphone;
a resistor equal to the rated source impedance, if not included in the amplifier or
–
the auxiliary equipment;
the headphone under test, which should be allowed to radiate freely in an un-
–
obstructed space.
The clipped noise signal at the output of the amplifier shall have a frequency distri-
2,2. The
and a peak-to-r.m.s ratio between 1,8 and
bution as specified in IEC 268-1,
amplifier shall be capable of supplying an output voltage of at least twice the rated
value of the long-term maximum source e.m.f., without clipping, and with a total
harmonic distortion of less than 10 %.
To verify the rated long-term maximum source e.m.f., that e.m.f. shall be applied to
b)
the headphone through the rated source impedance, under stated climatic conditions,
s duration. The head-
for 10 periods of 60 s, separated by periods of zero signal of
4 h.
phone shall then be stored under similar climatic conditions for at least
To verify the rated noise e.m.f., that e.m.f. shall be applied to the headphone
c)
through the rated source impedance, under static climatic conditions, for a continuous
period of 100 h. The headphone shall then be stored under similar climatic conditions
for at least 24 h.
The rated value of long-term maximum source e.m.f., or rated noise voltage, has
d)
been verified if, after the storage period, there is no significant change in any of the
characteristics of the headphone, so that it no longer complies with its specification.
NOTE — It may be inadvisable to use the same sample headphone to verify both characteristics, since the
application of both tests could be considered too severe.
3.3.3 Characteristic voltage
3.3.3.1 Characteristic to be specified
The sinusoidal source e.m.f. at 500 Hz which, when applied to the headphone through the
rated source impedance, produces a sound pressure level in the coupler or ear simulator
of 94 dB (ref 20 µPa).
NOTE — The frequency of 500 Hz is chosen to avoid the effects of diaphragm resonance, leakage and
standing waves that may occur in the coupler or ear simulator at other frequencies.

– 33 –
268-7 © IEC:1996
3.3.3.2 Method of measurement
The headphone is brought under standard conditions for measurement.
a)
The sinusoidal source e.m.f. at 500 Hz, applied through the rated source imped-
b)
ance, is then adjusted until a sound pressure level of 94 dB (ref 20 µPa) is obtained in
the coupler or ear simulator.
The source e.m.f. is then noted, and stated as the result.
c)
3.3.4 Protective devices
Characteristics to be specified
3.3.4.1
The protection voltage, which is the sinusoidal source e.m.f., applied through the
a)
rated source impedance, at which a device operates to protect the headphone from
damage or the user from excessive sound pressure level, (see also 1.6).
NOTES
If this voltage depends on frequency, the dependence should be presented graphically.
2 The limitation of excessive sound pressure level ("acoustic shock") in public telephone systems occurs at
a sound pressure level of 126 dB (ref 20 µPa) in some countries.
b) The effect (if any) of the operation of the device on the sound pressure produced by
the headphone.
c) The effect (if any) of the operation of the device on the impedance of the
headphone.
d) The damage limited source e.m.f., which is the maximum source e.m.f. that the
protective device can tolerate without damage. This is a rated condition.
3.3.4.2 Method of measurement
The headphone is brought under standard measuring conditions, and the signal is
a)
changed to a sinusoidal signal of variable voltage and frequency.
The source e.m.f., at the standard reference frequency, is increased until operation
b)
of the protective device causes a change of at least 1 dB in the sensitivity of the head-
phone. This voltage is noted, and measurements are then made of the impedance and
sound pressure level at voltages 1 dB lower and 1 dB higher than the noted voltage.
NOTE — At the 1 dB higher level, the impedance may be very high or very low, and the sound pressure may
be very low.
The measurements are then repeated, if necessary, at other frequencies.
c)
d) The source e.m.f. is then increased to the rated value of damage limited source
e.m.f., and any damage which results in a deviation from the specification is noted.
The measurements are then repeated, if necessary, at other frequencies. It may be
e)
necessary to repair damage or test other samples.
f) The results of the tests may be tabulated or expressed graphically.

268-7 © IEC:1996 - 35 -
3.4 Input power
For headphones in which the signal from the source equipment is directly applied to the
earphone(s), there is a characteristic expressed in terms of power corresponding to each
of the characteristics given in 3.3:
rated input power;
- rated long-term maximum input power;
rated noise power;
- characteristic power;
- characteristics a) and d) relating to protective devices (see 3.3.4.1).
Specifications in terms of power can be derived from the corresponding voltages (3.3) and
the rated impedance.
3.5 Sound pressure (level)
NOTE — To avoid continuous repetition of "sound pressure and/or sound pressure level", the abbreviation
"sound pressure (level)" is used.
3.5.1 Characteristics to be specified
a) The maximum sound pressure (level), which is the sound pressure (level) produced
in the coupler or ear simulator when the headphone is supplied with a sinusoidal
voltage of the rated source e.m.f. at 500 Hz, in series with the rated source impedance.
b) The working sound pressure (level), which is the sound pressure (level) produced in
the coupler or ear simulator, when the headphone is supplied with a sinusoidal voltage
at 500 Hz, in series with the rated source impedance, of such value that 1 mW would
be dissipated in a pure resistance equal to the rated impedance of the headphone,
connected in place of it.
NOTE — This characteristic is not relevant for headphones in which the signal from the source equipment is
not directly applied to the earphone(s).
3.5.2 Method of measurement
a) The headphone is brought under standard conditions for measurement, and a
sinusoidal signal of the rated source e.m.f. at 500 Hz is then applied in series with the
rated source impedance.
b) The sound pressure (level) in the coupler or ear simulator is then noted, and stated
as the result a) in 3.5.1.
The source e.m.f. is then adjusted so that the voltage across the input connector of
c)
the headphone is such that it would cause 1 mW to be dissipated in a pure resistance
equal to the rated impedance of the headphone.
d) The sound pressure (level) in the coupler or ear simulator is then noted, and stated
as the result b) in 3.5.1.
268-7 © IEC:1996 - 37 -
3.6 Frequency response
NOTE – Several different methods of measuring frequency response are specified in this standard because
no method has yet been developed that is universally applicable. Coupler or ear simulator measurements are
relatively simple, but the results bear little relation to those from subjective assessments.
They are most useful for production testing, quality control and commercial specifications. The two types of
subjective assessment themselves produce different results, as do the two types of ear canal sound pressure
level measurement. These methods are more time-consuming than coupler measurements, and are most
useful in product development and for small batch production of special products. No known objective method
produces a flat frequency response characteristic from an earphone which is subjectively judged to produce
wide band uncoloured reproduction.
3.6.1 Coupler or ear simulator (including HATS) frequency response
3.6.1.1 Characteristic to be specified
The variation of the sound pressure (level) in the coupler or ear simulator as a function of
frequency, when a sinusoidal voltage of variable frequency, under standard measuring
conditions, is applied to the headphone in series with the rated source impedance. The
type of coupler or ear simulator used shall be stated in the results.
NOTE – The value of this characteristic may also be deduced from measurements using narrowband or
wideband noise signals, or impulse signals. If one of these types of signal is used, it is the responsibility of
the test house to show that the results are equivalent to those obtained with sinusoidal signals.
3.6.1.2 Method of measurement
a) The headphone is brought under standard conditions for measurement, and a
sinusoidal source of variable frequency, at the rated source e.m.f., is applied in series
with the rated source impedance.
b) The frequency is then varied over at least the rated frequency range of the head-
phone (see 3.6.4), and the sound pressure (level) at each frequency is noted. This
should be done automatically, using a swept- or stepped-frequency source, and a chart
recorder or plotter. The chart speed and resolution, which should be stated by the
manufacturer, shall be chosen so that the specified accuracy of the results is obtained.
NOTE – If the direction of frequency sweep affects the results, the results with the frequency sweeping from
low to high should be used, and this should be stated in the results.
The results are presented graphically. If sound pressure level in decibels is
c)
plotted against frequency on a logarithmic scale, the preferred scale has the same
length representing 50 dB as represents one decade of frequency (see IEC 268-1 and
IEC 263).
3.6.2 Free-field comparison frequency response
3.6.2.1 Characteristic to be specified
The quotient, as a function of frequency, of the sound pressure of the reference-free
sound field by the source e.m.f. to the headphone which is required to produce a sound
subjectively equal in loudness to the free sound field. It is normally expressed in decibels
referred to the value at the standard reference frequency.

268-7 © IEC:1996 – 39 –
3.6.2.2 Method of measurement (direct)
In order to apply this method, it is necessary for two earphones, with sufficiently similar
frequency response to allow adequate accuracy of measurement, to be worn simulta-
neously by a test person (see annex D).
NOTE — Similarity of response within 2 dB is often sufficient.
a) The headphone is brought under free-field comparison conditions (see 2.4.1 and
annex B).
b) The test signals are 1/3 octave filtered bands of pink noise, covering at least the
rated frequency range (see 3.6.5). For each band, the test person listens alternately to
the free field, with the headphone removed, and then to the headphone, and the source
e.m.f. applied to the headphone, in series with the rated source impedance, is adjusted
until equal loudness is obtained. The adjustment may be performed by the test person
or the test supervisor, or automatically under computer control.
c) It has proved practical to begin the test sequence with the band centred on 1 kHz,
proceed higher in frequency to at least the upper limit of the rated frequency range,
continue the tests with descending centre frequencies, at least to the lower limit of the
rated frequency range, and then with increasing centre frequencies up to the 1 kHz
band.
d) The tests shall be repeated with at least eight test persons. The individual test
results differ due to differences in head and pinna shape and size (see annex D).
e) The results for all the test persons are averaged in each 1 octave band, and the
/3
resulting bar graph is presented as the free-field comparison frequency response of the
headphone. The standard deviation of the results in each band should be indicated on
the graph. The scales for the graph preferably shall be such that 50 dB is represented
by the same length as one decade of frequency.
3.6.2.3 Method of measurement (by substitution)
A headphone, whose free-field comparison frequency response has been measured as
described in 3.6.2.2, using a panel of at least 16 persons, may be used as a loudness
comparison reference for the measurement of other headphones. The reference
headphone shall be supplied with noise voltages equal to those obtained in its direct
measurement. The measurement shall be carried out in a quiet room, and the results,
calculated as described in 3.6.2.2, shall state that a substitution method has been used.
NOTE — The accuracy of this method is greater if the characteristics of the reference headphone and the
headphone being tested are similar.
3.6.3 Diffuse-field comparison frequency response
3.6.3.1 Characteristic to be specified
The quotient, as a function of frequency, of the sound pressure of the reference diffuse
sound field by the source e.m.f. to the headphone required to produce a sound sub-
jectively equal in loudness to the diffuse sound field. It is normally expressed in decibels
referred to the value at the standard reference frequency.

268-7 © I EC:1996 – 41 –
3.6.3.2 Method of measurement (direct)
In order to apply this method, it is necessary for two earphones, with sufficiently similar
frequency response to allow adequate accuracy of measurement, to be worn simulta-
neously by a test person (see annex D).
NOTE - Similarity of response within 2 dB is often sufficient.
a) The headphone is brought under diffuse-field comparison conditions (see 2.4.2 and
annex C).
/3 octave filtered bands of pink noise, covering at least the
b) The test signals are 1
rated frequency range (see 3.6.5). For each band, the test person listens alternately to
the diffuse field, with the headphone removed, then with the headphone, and adjusts
the source e.m.f. applied to the headphone, in series with the rated source impedance,
until equal loudness is obtained. The adjustment may be performed by the test person
or the test supervisor, or automatically under computer control.
c) It has proved practical to begin the test sequence with the band centred on 1 kHz;
proceed higher in frequency to at least the upper limit of the rated frequency range,
continue the tests with descending centre frequencies, at least to the lower limit of the
rated frequency range, and then with increasing centre frequencies up to the 1 kHz
band.
d
...