IEC 61094-2:2009

Electroacoustics - Measurement microphones - Part 2: Primary method for pressure calibration of laboratory standard microphones by the reciprocity technique

IEC 61094-2:2009 is applicable to laboratory standard microphones meeting the requirements of IEC 61094-1 and other types of condenser microphone having the same mechanical dimensions and specifies a primary method of determining the complex pressure sensitivity so as to establish a reproducible and accurate basis for the measurement of sound pressure. This second edition cancels and replaces the first edition published in 1992. This second edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- an update of Clause 6 to fulfil the requirements of ISO/IEC Guide 98-3;
- an improvement of the heat conduction theory in Annex A;
- a revision of Annex F: Physical properties of humid air.

Electroacoustique - Microphones de mesure - Partie 2: Méthode primaire pour l'étalonnage en pression des microphones étalons de laboratoire par la méthode de réciprocité

La CEI 61094-2:2009 est applicable aux microphones étalons de laboratoire répondant aux prescriptions de la CEI 61094-1 et aux autres types de microphones à condensateur présentant les mêmes dimensions mécaniques et spécifie une méthode primaire de détermination de l'efficacité en pression complexe de manière à établir une base reproductible et exacte pour la mesure de la pression acoustique. Cette deuxième édition annule et remplace la première édition publiée en 1992. Cette deuxième édition constitue une révision technique. Cette édition inclut les modification techniques majeures suivantes par rapport à l'édition précédente:
- une mise à jour de l'Article 6 afin d'être en conformité avec les exigences du Guide ISO/CEI 98-3;
- une amélioration de la théorie de la conduction thermique en Annexe A;
- une révision de l'Annexe F: Propriétés physiques de l'air humide.

General Information

• Status: Published
• Publication Date: 03-Feb-2022
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 17.140.50 - Electroacoustics
• Technical Committee: TC 29 - Electroacoustics
• Drafting Committee: WG 5 - TC 29/WG 5
• Current Stage: PPUB - Publication issued
• Start Date: 15-Mar-2009
• Completion Date: 20-Feb-2009

Relations

• Amended By: IEC 61094-2:2009/AMD1:2022 - Amendment 1 - Electroacoustics - Measurement microphones - Part 2: Primary method for pressure calibration of laboratory standard microphones by the reciprocity technique
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 61094-2 ®
Edition 2.0 2009-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electroacoustics – Measurement microphones –
Part 2: Primary method for pressure calibration of laboratory standard
microphones by the reciprocity technique

Electroacoustique – Microphones de mesure –
Partie 2: Méthode primaire pour l’étalonnage en pression des microphones
étalons de laboratoire par la méthode de réciprocité

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by
any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or
IEC's member National Committee in the country of the requester.
If you have any questions about IEC copyright or have an enquiry about obtaining additional rights to this publication,
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IEC 61094-2 ®
Edition 2.0 2009-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electroacoustics – Measurement microphones –
Part 2: Primary method for pressure calibration of laboratory standard
microphones by the reciprocity technique

Electroacoustique – Microphones de mesure –
Partie 2: Méthode primaire pour l’étalonnage en pression des microphones
étalons de laboratoire par la méthode de réciprocité

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
X
CODE PRIX
ICS 17.140.50 ISBN 978-2-88910-410-9
– 2 – 61094-2 © IEC:2009
CONTENTS
FOREWORD.4
1 Scope.6
2 Normative references .6
3 Terms and definitions .6
4 Reference environmental conditions .7
5 Principles of pressure calibration by reciprocity .7
5.1 General principles .7
5.1.1 General .7
5.1.2 General principles using three microphones .7
5.1.3 General principles using two microphones and an auxiliary sound
source .7
5.2 Basic expressions .8
5.3 Insert voltage technique .9
5.4 Evaluation of the acoustic transfer impedance.9
5.5 Heat-conduction correction.11
5.6 Capillary tube correction.11
5.7 Final expressions for the pressure sensitivity .12
5.7.1 Method using three microphones .12
5.7.2 Method using two microphones and an auxiliary sound source .12
6 Factors influencing the pressure sensitivity of microphones.13
6.1 General .13
6.2 Polarizing voltage.13
6.3 Ground-shield reference configuration.13
6.4 Pressure distribution over the diaphragm .13
6.5 Dependence on environmental conditions .14
6.5.1 Static pressure .14
6.5.2 Temperature.14
6.5.3 Humidity .14
6.5.4 Transformation to reference environmental conditions .15
7 Calibration uncertainty components .15
7.1 General .15
7.2 Electrical transfer impedance .15
7.3 Acoustic transfer impedance .15
7.3.1 General .15
7.3.2 Coupler properties.15
7.3.3 Microphone parameters .16
7.4 Imperfection of theory.17
7.5 Uncertainty on pressure sensitivity level.18
Annex A (normative) Heat conduction and viscous losses in a closed cavity .20
Annex B (normative) Acoustic impedance of a capillary tube.23
Annex C (informative) Examples of cylindrical couplers for calibration of microphones .26
Annex D (informative) Environmental influence on the sensitivity of microphones .31
Annex E (informative) Methods for determining microphone parameters .34
Annex F (informative) Physical properties of humid air.37

61094-2 © IEC:2009 – 3 –
Figure 1 – Equivalent circuit for evaluating the acoustic transfer impedance Z .9
a,12
Figure 2 – Equivalent circuit for evaluating Z’ when coupler dimensions are small
a,12
compared with wavelength.10
Figure 3 – Equivalent circuit for evaluating Z’ when plane wave transmission in the
a,12
coupler can be assumed .10
Figure C.1 – Mechanical configuration of plane-wave couplers .27
Figure C.2 – Mechanical configuration of large-volume couplers .29
Figure D.1 – Examples of static pressure coefficient of LS1P and LS2P microphones
relative to the low-frequency value as a function of relative frequency f/f .32
o
Figure D.2 – General frequency dependence of that part of the temperature coefficient
for LS1P and LS2P microphones caused by the variation in the impedance of the
enclosed air .33

Table 1 – Uncertainty components .19
Table A.1 – Values for E .21
V
Table B.1 – Real part of Z in gigapascal-seconds per cubic metre (GPa⋅s/m ).24
a,C
Table B.2 – Imaginary part of Z in gigapascal-seconds per cubic metre (GPa⋅s/m ).25
a,C
Table C.1 – Nominal dimensions for plane-wave couplers.28
Table C.2 – Nominal dimensions and tolerances for large-volume couplers .29
Table C.3 – Experimentally determined wave-motion corrections for the air-filled large-
volume coupler used with type LS1P microphones.
Table F.1 – Calculated values of the quantities in Clauses F.1 to F.5 for two sets of
environmental conditions .40
Table F.2 – Coefficients used in the equations for humid air properties.41

– 4 – 61094-2 © IEC:2009
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTROACOUSTICS –
MEASUREMENT MICROPHONES –
Part 2: Primary method for pressure calibration of laboratory
standard microphones by the reciprocity technique

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,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). 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. 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 Com
...

IEC 61094-2 ®
Edition 2.1 2022-02
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electroacoustics – Measurement microphones –
Part 2: Primary method for pressure calibration of laboratory standard
microphones by the reciprocity technique

Électroacoustique – Microphones de mesure –
Partie 2: Méthode primaire pour l’étalonnage en pression des microphones
étalons de laboratoire par la méthode de la réciprocité

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite
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International Standards for all electrical, electronic and related technologies.

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IEC 61094-2 ®
Edition 2.1 2022-02
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electroacoustics – Measurement microphones –
Part 2: Primary method for pressure calibration of laboratory standard
microphones by the reciprocity technique
Électroacoustique – Microphones de mesure –
Partie 2: Méthode primaire pour l’étalonnage en pression des microphones
étalons de laboratoire par la méthode de la réciprocité
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.140.50 ISBN 978-2-8322-4761-7

IEC 61094-2 ®
Edition 2.1 2022-02
CONSOLIDATED VERSION
REDLINE VERSION
VERSION REDLINE
colour
inside
Electroacoustics – Measurement microphones –
Part 2: Primary method for pressure calibration of laboratory standard
microphones by the reciprocity technique

Électroacoustique – Microphones de mesure –
Partie 2: Méthode primaire pour l’étalonnage en pression des microphones
étalons de laboratoire par la méthode de la réciprocité

– 2 – IEC 61094-2:2009+AMD1:2022 CSV
 IEC 2022
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Reference environmental conditions . 8
5 Principles of pressure calibration by reciprocity . 8
5.1 General principles . 8
5.1.1 General . 8
5.1.2 General principles using three microphones . 8
5.1.3 General principles using two microphones and an auxiliary sound
source . 8
5.2 Basic expressions . 9
5.3 Insert voltage technique . 10
5.4 Evaluation of the acoustic transfer impedance . 10
5.5 Heat-conduction correction . 12
5.6 Capillary tube correction . 13
5.7 Final expressions for the pressure sensitivity . 13
5.7.1 Method using three microphones . 13
5.7.2 Method using two microphones and an auxiliary sound source . 14
6 Factors influencing the pressure sensitivity of microphones . 14
6.1 General . 14
6.2 Polarizing voltage . 14
6.3 Ground-shield reference configuration . 14
6.4 Pressure distribution over the diaphragm . 15
6.5 Dependence on environmental conditions . 15
6.5.1 Static pressure . 15
6.5.2 Temperature . 15
6.5.3 Humidity . 16
6.5.4 Transformation to reference environmental conditions . 16
6.6 Influence of leakage . 16
7 Calibration uncertainty components . 16
7.1 General . 16
7.2 Electrical transfer impedance . 16
7.3 Acoustic transfer impedance . 17
7.3.1 General . 17
7.3.2 Coupler properties . 17
7.3.3 Microphone parameters . 18
7.4 Imperfection of theory. 19
7.5 Uncertainty on pressure sensitivity level . 19
Annex A (normative) Heat conduction and viscous losses in a closed cavity . 22
A.1 General . 22
A.2 Low frequency solution . 22
A.3 Broad-band solution . 25
A.4 Reference documents. 26
Annex B (normative) Acoustic impedance of a capillary tube. 27

 IEC 2022
B.1 General . 27
B.2 Reference document . 29
Annex C (informative) Examples of cylindrical couplers for calibration of microphones . 30
C.1 General . 30
C.2 Plane-wave couplers . 30
C.3 Large-volume couplers . 32
C.4 Reference documents. 34
Annex D (informative) Environmental influence on the sensitivity of microphones . 35
D.1 General . 35
D.2 Basic relations . 35
D.3 Dependence on static pressure . 35
D.4 Dependence on temperature . 36
D.5 Reference documents. 37
Annex E (informative) Methods for determining microphone parameters . 38
E.1 General . 38
E.2 Front cavity depth . 38
E.3 Front cavity volume and equivalent volume . 38
E.4 Acoustic impedance of the microphone . 39
E.5 Reference documents. 40
Annex F (informative) Physical properties of humid air . 41
F.1 General . 41
F.2 Density of humid air . 42
F.3 Speed of sound in air .
...