IEC 60268-4:2010

IEC 60268-4 ®
Edition 4.0 2010-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Sound system equipment –
Part 4: Microphones
Équipements pour systèmes électroacoustiques –
Partie 4: Microphones
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IEC 60268-4 ®
Edition 4.0 2010-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Sound system equipment –
Part 4: Microphones
Équipements pour systèmes électroacoustiques –
Partie 4: Microphones
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
X
CODE PRIX
ICS 33.160.50 ISBN 978-2-88912-156-4
– 2 – 60268-4 © IEC:2010
CONTENTS
FOREWORD.6

1 Scope.8

2 Normative references.8

3 General conditions.9

3.1 General .9

3.2 Measurement conditions .9

3.2.1 General .9

3.2.2 Rated conditions .10
4 Particular conditions .11
4.1 Pre-conditioning .11
4.2 Sound source .11
4.3 Measurement of sound pressure.11
4.4 Voltage measuring system .11
4.5 Acoustical environment.11
4.5.1 General .11
4.5.2 Free-field conditions .11
4.5.3 Diffuse field conditions.13
4.5.4 Microphone coupled to a sound source by means of a small cavity
coupler .14
4.6 Methods of measuring frequency response .14
4.6.1 Point-by-point and continuous sweep frequency methods .14
4.6.2 Calibration methods .15
4.7 Overall accuracy.15
4.8 Graphical presentation of results.15
5 Type description (acoustical behaviour).16
5.1 Principle of the transducer .16
5.2 Type of microphone .16
5.3 Type of directional response characteristics.16
6 Terminals and controls.16
6.1 Marking .16
6.2 Connectors and electrical interface values .16
7 Reference point and axis .16

7.1 Reference point .16
7.2 Reference axis .16
8 Rated power supply .17
8.1 Characteristic to be specified.17
8.2 Method of measurement .17
9 Electrical impedance.17
9.1 Internal impedance .17
9.1.1 Characteristic to be specified .17
9.1.2 Methods of measurement.17
9.2 Rated impedance.18
9.3 Minimum permitted load impedance .18
10 Sensitivity.18
10.1 General .18
10.2 Sensitivities with respect to acoustical environment.19

60268-4 © IEC:2010 – 3 –
10.2.1 Free-field sensitivity.19

10.2.2 Diffuse-field sensitivity .19

10.2.3 Close-talking sensitivity.20

10.2.4 Pressure sensitivity.21

10.3 Sensitivities with respect to nature of signal .21

10.3.1 Rated sensitivity .21

10.3.2 Characteristic sensitivity for speech .21

11 Response .22

11.1 Frequency response .22

11.1.1 Characteristic to be specified .22
11.1.2 Method of measurement .23
11.2 Effective frequency range .23
11.2.1 Characteristic to be specified .23
11.2.2 Method of measurement .23
12 Directional characteristics .23
12.1 Directional pattern .23
12.1.1 Characteristic to be specified .23
12.1.2 Methods of measurement.23
12.2 Directivity index .25
12.2.1 Characteristic to be specified .25
12.2.2 Method of measurement .25
12.3 Front-to-rear sensitivity index (0° – 180°) .25
12.3.1 Characteristic to be specified .25
12.3.2 Method of measurement .25
12.4 Noise-cancelling index .25
12.4.1 Characteristic to be specified .25
12.4.2 Method of measurement .26
12.5 Special characteristics for stereo microphones.26
12.5.1 General .26
12.5.2 Included angle of an XY (left-right) microphone .26
12.5.3 Acceptance angle .26
12.5.4 Threshold angle.27
13 Amplitude non-linearity .27
13.1 General .27
13.2 Total harmonic distortion .27

13.2.1 Characteristics to be specified .27
13.2.2 Method of measurement .27
th
13.3 Harmonic distortion of the n order (n = 2, 3,.) .28
13.3.1 Characteristic to be specified .28
13.3.2 Method of measurement .28
13.4 Difference frequency distortion of second order.29
13.4.1 Characteristic to be specified .29
13.4.2 Method of measurement .29
14 Limiting characteristics .29
14.1 Rated maximum permissible peak sound pressure.29
14.2 Overload sound pressure.30
14.2.1 Characteristic to be specified .30
14.2.2 Method of measurement .30
15 Balance .30

– 4 – 60268-4 © IEC:2010
15.1 Balance of the microphone output.30

15.2 Balance under working conditions .30

16 Equivalent sound pressure level due to inherent noise.31

16.1 Characteristic to be specified.31

16.2 Method of measurement .31

17 Ambient conditions .32

17.1 General .32

17.2 Pressure range.32

17.3 Temperature range .32

17.4 Relative humidity range .32
18 External influences .32
18.1 General .32
18.1.1 Specification and measuring methods .32
18.1.2 Other external interferences.32
18.2 Equivalent sound pressure due to external magnetic fields.33
18.2.1 Characteristic to be specified .33
18.2.2 Method of measurement .33
18.3 Equivalent sound pressure due to mechanical vibration.33
18.3.1 Characteristic to be specified .33
18.3.2 Method of measurement .34
18.4 Equivalent sound pressure due to wind .34
18.4.1 Characteristic to be specified .34
18.4.2 Method of measurement .34
18.5 Transient equivalent sound pressure due to "pop" effect .37
18.5.1 Characteristic to be specified .37
18.5.2 Method of measurement .38
18.6 Equivalent sound pressure due to electromagnetic interference.39
18.6.1 General .39
18.6.2 Characteristic to be specified .39
18.6.3 Method of measurement .39
18.7 Electrostatic discharge.40
19 Magnetic stray field.40
19.1 Characteristic to be specified.40
19.2 Method of measurement .40
20 Physical characteristics.40

20.1 Dimensions .40
20.2 Weight.40
20.3 Cables and connectors .40
21 Classification of the characteristics to be specified.40
21.1 General .40
Annex A (normative) Sound insulation device .43
Annex B (informative) Simplified procedure for “pop” measurements .44
Annex C (informative) Supplement for digital microphones .47
Bibliography .49

Figure 1 – Balance of the output.30
Figure 2 – Balance under working conditions .31

60268-4 © IEC:2010 – 5 –
Figure 3 – Measurement set-up for wind influence .35

Figure 4 – Wind generators, type 1 (Figure 4a) and type 2 (Figure 4b)).36

Figure 5 – Electrical and mechanical set-up for the measuring of the "pop" effect .38

Figure A.1 – Sound insulation device.43

Figure B.1 – Measurement set-up.45

Figure B.2 – Test fixture for the sound field sensitivity .46

Table 1 – Reverberation time of the empty room.14

Table 2 – Speech power weighting factor at octave-band centre frequencies .22
Table 3 – Reference signal and characteristics.39
Table 4 – Classification of characteristics .42
Table C.1 – Classification of the characteristics to be specified .47
Table C.2 – Additional digital characteristics to be specified .48

– 6 – 60268-4 © IEC:2010
INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
SOUND SYSTEM EQUIPMENT –
Part 4: Microphones
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
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Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
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governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60268-4 has been prepared by IEC technical committee 100: Audio,
video and multimedia systems and equipment.
This fourth edition cancels and replaces the third edition published in 2004, and constitutes a
technical revision.
The main changes with respect to the previous edition are the following:
– correction of noise measurement,
– added annex for digital microphones,
– added requirement for tolerances in data to be specified.

60268-4 © IEC:2010 – 7 –
This bilingual version (2010-09) replaces the English version.

The text of this standard is based on the following documents:

FDIS Report on voting
100/1678/FDIS 100/1707/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.

The French version of this standard has not been voted upon.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 60268 series, under the general title “Sound system equipment”,
can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until the
stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to
the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 8 – 60268-4 © IEC:2010
SOUND SYSTEM EQUIPMENT –
Part 4: Microphones
1 Scope
This part of IEC 60268 specifies methods of measurement for the electrical impedance,

sensitivity, directional response pattern, dynamic range and external influences of sound
system microphones, and also details the characteristics to be specified by the manufacturer.
It applies to sound system microphones for all applications for speech and music. It does not
apply to measurement microphones, but it does apply to each audio channel of microphones
having more than one channel, for example for stereo or similar use. It is also applicable to
flush-mounted microphones and to the analogue characteristics of microphones with digital
audio output.
For the purposes of this International Standard, a microphone includes all such devices as
transformers, pre-amplifiers, or other elements that form an integral part of the microphone, up
to the output terminals specified by the manufacturer.
NOTE The characteristics specified in this standard do not completely describe the subjective response of the
microphone. Further work is necessary to find new definitions and measurement procedures for a later replacement
by objective characteristics of at least some of the subjective descriptions used to describe microphone
performance.
2 Normative references
The following referenced documents are indispensable for the application of this document. For
dated references, only the edition cited applies. For undated references, the latest edition of
the referenced document (including any amendments) applies.
IEC 60065:2001, Audio, video and similar electronic apparatus – Safety requirements
Amendment 1 (2005)
IEC 60268-1:1985, Sound system equipment – Part 1: General
Amendment 1 (1988)
Amendment 2 (1988)
IEC 60268-2:1987, Sound system equipment – Part 2: Explanation of general terms and
calculation methods
Amendment 1 (1991)
IEC 60268-3:2000, Sound system equipment – Part 3: Amplifiers
IEC 60268-5:2003, Sound system equipment – Part 5: Loudspeakers
Amendment 1 (2007)
IEC 60268-11:1987, Sound system equipment – Part 11: Application of connectors for the
interconnection of sound system components
Amendment 1 (1989)
Amendment 2 (1991)
60268-4 © IEC:2010 – 9 –
IEC 60268-12:1987, Sound system equipment – Part 12: Application of connectors for
broadcast and similar use
Amendment 1 (1991)
Amendment 2 (1994)
IEC 61000-4-2:1995, Electromagnetic compatibility (EMC) – Part 4-2: Testing and measure-

ment techniques – Electrostatic discharge immunity test

IEC 61000-4-3:2006, Electromagnetic compatibility (EMC) – Part 4-3: Testing and

measurement techniques – Radiated, radio-frequency, electromagnetic field immunity test

Amendment 1 (2007)
IEC 61265:1995, Electroacoustics – Instruments for measurement of aircraft noise – Perform-
ance requirements for systems to measure one-third-octave-band sound pressure levels in
noise certification of transport-category aeroplanes
IEC 61938:1996, Audio, video and audiovisual systems – Interconnections and matching
values – Preferred matching values of analogue signals
ISO 354:2003, Acoustics – Measurement of sound absorption in a reverberation room
ITU-T Recommendation P.51:1996, Artificial mouth
3 General conditions
3.1 General
Special reference is made to IEC 60268-1, concerning:
• units and system of measurement;
• frequencies of measurement;
• quantities to be specified and their accuracy (see also 4.7);
• marking (see also 6.1);
• ambient conditions;
• filters, networks and measuring instruments for noise specification and measurement;
• individual specifications and type specifications;
• graphical presentation of characteristics;

• scales for graphical presentation;
• personal safety and prevention of spread of fire;
• method of producing a uniform alternating magnetic field;
• search coils for measuring the magnetic field strength,
and to IEC 61938 concerning powering of microphones.
3.2 Measurement conditions
3.2.1 General
For convenience in specifying how microphones shall be set up for measurement, a set of
conditions has been defined in this recommendation under the title of "rated conditions".
Three ratings are basic to the formulation of these concepts:

– 10 – 60268-4 © IEC:2010
– rated impedance (see 9.2);
– rated power supply (see 8.1);

– rated sensitivity (see 10.3.1).

To obtain the correct conditions for measurement, the above mentioned ratings shall be taken

from the specifications supplied by the manufacturer of the equipment.

The term "rated" applied to other characteristics relates to the specification or measurement of

the particular characteristic under rated conditions or under conditions unambiguously

connected to them. This applies, for example, to the following two characteristics:

– rated output voltage;
– rated equivalent sound pressure level due to inherent noise.
Methods of measurement are given in this standard for electrical impedance, sensitivity,
directional pattern, dynamic range and external influences. Where alternative methods are
given, the chosen method shall be specified.
3.2.2 Rated conditions
The microphone is understood to be working under rated conditions when the following
conditions are fulfilled:
– the microphone shall operate under no-load conditions (see 9.2);
– if the microphone needs a power supply, this shall be the rated power supply;
– the microphone (except a close-talking microphone) shall be placed in a sound field
meeting the free-field conditions in 4.5.2, the waves having zero degree incidence with
respect to the reference direction;
– the undisturbed sound pressure (in the absence of the microphone) in the sound field at the
reference point of the microphone shall be sinusoidal and set at a level of 1 Pa (94 dB SPL);
– for close-talking microphones, the microphone shall be placed at a stated distance, no
more than 25 mm from the artificial mouth complying with ITU-T P.51, and the undisturbed
sound pressure in the sound field at the reference point of microphone shall be sinusoidal
and set at a level of 3 Pa (104 dB SPL);
– if a special microphone needs a different measurement level, this shall be stated in the
technical data together with the reason for this. Levels related to the normal reference level
of 94 dB by multiples of 10 dB are preferred;
– controls, if any, shall be set to the position recommended by the manufacturer;
– in the absence of a clear reason to the contrary, the measurement frequency shall
be 1 000 Hz (see IEC 60268-1);

– the ambient pressure, the relative humidity and the ambient temperature shall be within the
limits given in IEC 60268-1, and shall be stated;
– measurements may be made at a sound pressure of 0,3 Pa if this is necessary due to
limitations of the performance of the loudspeaker.
NOTE 1 An artificial voice which emits a signal simulating that emitted by the nose should be used for measuring
pressure-gradient close-talking microphones to ensure that nasal sounds are adequately reproduced. The absence
of such sounds in the reproduction may give rise to unnatural speech quality.
NOTE 2 Limitations of the measurement site or the measurement equipment may also require the use of other
than the given measurement sound pressure levels. This is acceptable only if any change in performance between
the level used and the reference level are known with the necessary accuracy for the relevant characteristics.

60268-4 © IEC:2010 – 11 –
4 Particular conditions
4.1 Pre-conditioning
A microphone with preamplifier shall be switched on for the period of time specified by the

manufacturer, before measurements are made, to allow the components to reach the stationary

temperature for rated conditions. If the manufacturer specifies no period, a period of 10 s shall

be allowed for stabilization. If the microphone contains a vacuum tube or other heating device

the time shall be 10 min.
4.2 Sound source
The sound source shall be capable of producing at the microphone position the sound pressure
level as defined for rated conditions. The amplitude non-linearity of the sound source shall be
held to such a value that the effect on the measured response does not exceed 0,5 dB. If the
conditions of measurement preclude the possibility of securing sufficiently low distortion, a
narrow-band filter may be used at the microphone output terminals, which allows the response
at the fundamental frequency to be measured.
For free-field calibration and calibration of performance microphones, the sound source shall
be contained in an enclosure which radiates sound from one well-defined opening only, and
such an opening shall be radially symmetrical with respect to the axis of the reference direction
of the microphone.
4.3 Measurement of sound pressure
A calibrated reference pressure microphone shall be used to measure the sound pressure. The
reference microphone should be calibrated with an accuracy of ±1 dB or better.
4.4 Voltage measuring system
The electromotive force (e.m.f.) generated by the microphone, when in a sound field, shall be
determined by measuring the open-circuit voltage of the microphone using a voltmeter with an
input impedance of at least 100 times the rated impedance of the microphone. If external
equipment, such as a power supply, places a load on the microphone, the true e.m.f. shall be
calculated by correcting for the effect of this load.
4.5 Acoustical environment
4.5.1 General
The microphone can be measured in different acoustical environments:

a) in a free field or similar with neglectable boundary effects, e.g. by using special computer-
generated sound source signals:
– spherical waves, or
– plane waves, or
– waves produced by a specific sound source (artificial mouth or artificial head);
b) in a diffuse field;
c) coupled to a sound source by means of a small cavity (coupler).
4.5.2 Free-field conditions
4.5.2.1 General
A free-field sound wave is normally divergent in character. In certain circumstances it can
approximate an ideal plane wave.

– 12 – 60268-4 © IEC:2010
Free-field conditions can be obtained:

– in open air, ambient noise and wind permitting, or

– in an anechoic room, or
– in a duct.
A sound source of small dimensions with respect to the wavelength produces a spherical wave

in these environments. The spherical wave can be approximated to a plane wave in a region of

measurement located at a sufficient distance from the source. Spherical waves can be used to

measure pressure microphones but it is necessary to use almost perfect plane waves in the

low frequency range for the measurement of pressure gradient microphones.

For microphones responding both to pressure and to pressure gradient, having a sufficiently
flat frequency response in a plane-wave free sound field (i.e. at a sufficient distance from the
source), the response as a function of frequency f of distance r from a centre of spherical
diverging waves and of angle of incidence θ of the waves at the microphone, can be given in a
complex form:
⎛ 1 ⎞
(1−B) +B⎜1+ ⎟cosθ
⎜ ⎟
jkr
⎝ ⎠
where
1–B is the contribution of the pressure component;
B is the contribution of the pressure gradient component;
k = 2π/λ or 2πf/v;
B = 0 for the omnidirectional pressure type;
B = 0,5 for the cardioid type;
B = 1 for the bidirectional pressure gradient type.
At low frequencies, it becomes difficult to realize plane wave conditions in an anechoic room. A
plane wave at low frequencies, below the cut-off frequency of the anechoic room, can therefore
be better produced under other conditions.
Free-field conditions are considered to be sufficiently realized in the region around the
microphone if the following conditions are met:
– within a distance of 200 mm in front, behind, right, left, above and below the position of the
microphone the sound pressure level is measured at every measuring frequency by means
of a pressure transducer;
– the axis of the transducer shall point towards the reference point of the loudspeaker (see
IEC 60268-5);
– the corresponding sound pressure levels on axis positioned at different distances from the
loudspeaker shall not differ by more than 0,5 dB from the calculated levels in the ideal
sound field;
– the values at a nearly constant distance to the sound source, right, left, above and below
the microphone shall not differ by more than 1 dB from the level at the reference point of
the microphone.
4.5.2.2 Spherical waves
The sound pressure generated in a free field by an omnidirectional sound source varies
inversely with the distance from the acoustic centre of the sources.

60268-4 © IEC:2010 – 13 –
The output voltage of the microphone varies inversely with the distance between the source

and the microphone when the relevant dimensions of both are small compared with the

wavelength, allowing the results from the measurements made at a certain distance r to be

converted by calculation to results which would be obtained at the reference distance.

When either the circumference of the radiating surface of the source or the circumference of

the principal acoustic entry of the microphone exceeds the wavelength, this computation

applies only when the measuring distance conforms to:

r ≥d
r ≥ d / λ
where
r is the distance from the source to the measuring point;
d is the effective diameter of the sound source;
λ is the sound wavelength.
NOTE It is advisable for the distance from the source to the measuring point to exceed three times the largest
dimension of the radiating surface of the source.
4.5.2.3 Plane progressive waves
A plane progressive wave can be obtained either in a duct or in a free field.
a) In a duct
In designing a duct capable of producing useful results, there are many problems to be
solved such as the design of the terminating impedance, the avoidance of cross-modes, the
shape of the original wavefront and the relative dimensions of the duct and the microphone.
b) In a free field
A spherical wave at a distance of at least half the wavelength from the centre of curvature
at the lowest frequency of measurement is a practical approximation to a plane progressive
wave.
NOTE It should be understood that for measurement of "shotgun" types and pressure zone microphones,
determining the smallest permitted distance is complicated and no exact rules can be given. Therefore, in these
cases the measuring distance used should be stated.
4.5.2.4 Use of an artificial mouth
In order that the conditions of test may be similar to those of actual use, it is necessary to
introduce an obstacle in the shape of a human head when measuring close-talking
microphones by means of an artificial mouth (see Note 1 to 3.2.2).
4.5.3 Diffuse field conditions
Some measurements can be made in a diffuse field in which sound waves are propagated with
random incidence. In this case, bands of noise of third-octave width or broadband signals
together with suitable filtering shall be used.
A diffuse sound field can be approximately realized in a reverberant room characterized by a
sufficiently long duration of reverberation at a sufficiently large distance from the source and
the walls, and above a limiting frequency (see also ISO 354).
The reverberation time T of the empty room is specified in Table 1.

– 14 – 60268-4 © IEC:2010
Table 1 – Reverberation time of the empty room

T > 5 s 5 s 5 s 4,5 s 3,5 s 2 s

at 125 Hz 250 Hz 500 Hz 1 000 Hz 2 000 Hz 4 000 Hz

For the determination of the lower frequency limit, the
...