IEC 60500:2017

IEC 60500 ®
Edition 2.0 2017-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Underwater acoustics – Hydrophones – Properties of hydrophones in the
frequency range 1 Hz to 500 kHz

Acoustique sous-marine – Hydrophones – Propriétés des hydrophones dans la
bande de fréquences de 1 Hz à 500 kHz

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
ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie
et les microfilms, sans l'accord écrit de l'IEC ou du Comité national de l'IEC du pays du demandeur. Si vous avez des
questions sur le copyright de l'IEC ou si vous désirez obtenir des droits supplémentaires sur cette publication, utilisez
les coordonnées ci-après ou contactez le Comité national de l'IEC de votre pays de résidence.

IEC Central Office Tel.: +41 22 919 02 11
3, rue de Varembé Fax: +41 22 919 03 00
CH-1211 Geneva 20 info@iec.ch
Switzerland www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.

IEC Catalogue - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
The stand-alone application for consulting the entire The world's leading online dictionary of electronic and
bibliographical information on IEC International Standards, electrical terms containing 20 000 terms and definitions in
Technical Specifications, Technical Reports and other English and French, with equivalent terms in 16 additional
documents. Available for PC, Mac OS, Android Tablets and languages. Also known as the International Electrotechnical
iPad. Vocabulary (IEV) online.

IEC publications search - www.iec.ch/searchpub IEC Glossary - std.iec.ch/glossary
The advanced search enables to find IEC publications by a 65 000 electrotechnical terminology entries in English and
variety of criteria (reference number, text, technical French extracted from the Terms and Definitions clause of
committee,…). It also gives information on projects, replaced IEC publications issued since 2002. Some entries have been
and withdrawn publications. collected from earlier publications of IEC TC 37, 77, 86 and

CISPR.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Customer Service Centre - webstore.iec.ch/csc
details all new publications released. Available online and If you wish to give us your feedback on this publication or
also once a month by email. need further assistance, please contact the Customer Service
Centre: csc@iec.ch.
A propos de l'IEC
La Commission Electrotechnique Internationale (IEC) est la première organisation mondiale qui élabore et publie des
Normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications IEC
Le contenu technique des publications IEC est constamment revu. Veuillez vous assurer que vous possédez l’édition la
plus récente, un corrigendum ou amendement peut avoir été publié.

Catalogue IEC - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
Application autonome pour consulter tous les renseignements
Le premier dictionnaire en ligne de termes électroniques et
bibliographiques sur les Normes internationales,
électriques. Il contient 20 000 termes et définitions en anglais
Spécifications techniques, Rapports techniques et autres
et en français, ainsi que les termes équivalents dans 16
documents de l'IEC. Disponible pour PC, Mac OS, tablettes
langues additionnelles. Egalement appelé Vocabulaire
Android et iPad.
Electrotechnique International (IEV) en ligne.

Recherche de publications IEC - www.iec.ch/searchpub
Glossaire IEC - std.iec.ch/glossary
65 000 entrées terminologiques électrotechniques, en anglais
La recherche avancée permet de trouver des publications IEC
en utilisant différents critères (numéro de référence, texte, et en français, extraites des articles Termes et Définitions des
comité d’études,…). Elle donne aussi des informations sur les publications IEC parues depuis 2002. Plus certaines entrées
projets et les publications remplacées ou retirées. antérieures extraites des publications des CE 37, 77, 86 et

CISPR de l'IEC.
IEC Just Published - webstore.iec.ch/justpublished

Service Clients - webstore.iec.ch/csc
Restez informé sur les nouvelles publications IEC. Just
Published détaille les nouvelles publications parues. Si vous désirez nous donner des commentaires sur cette
Disponible en ligne et aussi une fois par mois par email. publication ou si vous avez des questions contactez-nous:
csc@iec.ch.
IEC 60500 ®
Edition 2.0 2017-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Underwater acoustics – Hydrophones – Properties of hydrophones in the

frequency range 1 Hz to 500 kHz

Acoustique sous-marine – Hydrophones – Propriétés des hydrophones dans la

bande de fréquences de 1 Hz à 500 kHz

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.140.50 ISBN 978-2-8322-4049-6

– 2 – IEC 60500:2017 © IEC 2017
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Symbols . 11
5 Hydrophone characteristics . 12
5.1 General . 12
5.2 Basic requirements . 12
5.3 Sensitivity . 12
5.4 Frequency response . 13
5.4.1 Stated operating frequency band . 13
5.4.2 Frequency dependence . 13
5.5 Directional response . 13
5.6 Dynamic range . 13
5.6.1 Linearity and overload sound pressure level . 13
5.6.2 Equivalent noise pressure spectral density level . 14
5.6.3 Conditions required . 14
5.7 Electrical requirements . 14
5.7.1 Electromagnetic interference . 14
5.7.2 Electrical characteristics . 14
5.8 Mechanical requirements . 14
5.9 Environmental aspects . 15
5.10 Stability of the sensitivity . 15
5.10.1 Temperature stability . 15
5.10.2 Depth stability . 15
5.10.3 Time stability . 15
6 Information to be supplied by the manufacturer . 16
Annex A (informative) Recommendations for selecting hydrophones . 18
A.1 General . 18
A.2 Sensitivity . 18
A.3 Self–noise performance . 19
A.4 Frequency response . 19
A.5 Directional response . 20
A.6 Dynamic range . 20
A.7 Electrical connection . 21
A.8 Stability of the sensitivity . 21
A.8.1 Temperature stability . 21
A.8.2 Depth stability . 21
A.8.3 Time stability . 21
Bibliography . 22

Figure 1 – Angular co-ordinate system . 6

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
UNDERWATER ACOUSTICS – HYDROPHONES – PROPERTIES OF
HYDROPHONES IN THE FREQUENCY RANGE 1 Hz TO 500 kHz

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 Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
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 60500 has been prepared by IEC technical committee 87:
Ultrasonics.
This second edition cancels and replaces the first edition published in 1974. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition.
a) The format and scope of IEC 60500 have been changed to be compatible with
IEC 62127-3:2007 in accordance with ISO/IEC Directives, and has a good conformity with
IEC 60565:2006, making the suite of available standards for underwater sound a more
coordinated and coherent system.
b) The upper limit of the frequency range of hydrophones has been expanded from 100 kHz
to 500 kHz.
c) Technical requirements of hydrophone selecting are provided in Annex A, and the depth
range of the static pressure range of hydrophones has been expanded from 10 m to 100 m.

– 4 – IEC 60500:2017 © IEC 2017
The text of this International Standard is based on the following documents:
FDIS Report on voting
87/644/FDIS 87/649/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
UNDERWATER ACOUSTICS – HYDROPHONES – PROPERTIES OF
HYDROPHONES IN THE FREQUENCY RANGE 1 Hz TO 500 kHz

1 Scope
This document specifies the relevant characteristics and properties of hydrophones in the
frequency range 1 Hz to 500 kHz, and specifies how to report these characteristics. It does
not cover performance requirements for specific hydrophone types, or for specific hydrophone
applications. However, guidance on the choice of a hydrophone with appropriate performance
for a specific application is given in an informative annex.
This document is applicable to:
• hydrophones employing piezoelectric sensor elements, designed to respond to sound
pressure in water and measure underwater acoustical signals;
• hydrophones with or without an integral pre-amplifier.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements 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.
ISO 266:1997, Acoustics – Preferred frequencies
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
angular co-ordinate system
system used to designate the directional response pattern of the hydrophone
Note 1 to entry: The terms “horizontal directional response” and “vertical directional response” are often used for
representation of directional response in the xy-plane, and xz- (or yz-) planes respectively.
Note 2 to entry: “+z” is coincident with an axis of the hydrophone, and “−z” is in the direction of the hydrophone
cable.
– 6 – IEC 60500:2017 © IEC 2017
z
θ
r
y
φ
x
IEC
Key
r radial distance
θ polar angle
ϕ azimuthal angle
Figure 1 – Angular co-ordinate system
3.2
end-of-cable capacitance
C
H
electrical capacitance measured at the end of the integral cable of a
hydrophone at a frequency well below any pronounced resonance
Note 1 to entry: End-of-cable capacitance is expressed in farad, F.
Note 2 to entry: The frequency is stated along with the value of end-of-cable capacitance. The end-of cable
capacitance is typically measured at a frequency of 1 kHz.
3.3
diffraction factor
ratio of the root-mean-square sound pressure averaged over the part of the hydrophone
designed to receive an incident plane wave sound pressure from a given direction to the free-
field root-mean-square sound pressure that would exist at the reference centre of the
hydrophone if the hydrophone was removed
[SOURCE: IEC 60565:2006 [1] , 3.4, modified – Replace “averaged pressure” with “root-
mean-square sound pressure averaged”, “receive sound” with “receive an incident plane wave
sound pressure from a given direction”, “free-field sound pressure” with “free-field root-mean-
square sound pressure”, and add “if the hydrophone was removed”.]
3.4
directional response
description, generally presented graphically, of the response of a
hydrophone, as a function of the direction of propagation of the incident plane sound wave, in
a specified plane through the reference centre, at a specified frequency
Note 1 to entry: The directional response pattern is usually presented in the form of a two dimensional polar
graph. The scale of the polar may be in terms of sensitivity level or as relative values normalized to the sensitivity
in a specified direction (often the direction of the principal axis). The relative values are sometimes presented in
decibels as a relative directional response level. See Figure 1 for description of angular co-ordinate system.
___________
Numbers in square brackets refer to the Bibliography.

[SOURCE: IEC 62127-3:2007 [2], 3.1, modified – Add the specific context " hydrophone>" and Note 1 to entry.]
3.5
dynamic range
twenty times the logarithm to the base 10 of the ratio of the overload sound pressure in a
specified frequency band that produces an undistorted hydrophone output to the equivalent
bandwidth noise pressure at the hydrophone
Note 1 to entry: Dynamic range is expressed in decibel, dB.
[SOURCE: IEC 60565:2006 [1], 3.6, modified – Replace “ratio” with “twenty times the
logarithm to the base 10 of the ratio”, “maximum free-field sound pressure” with “overload
sound pressure in a specified frequency band”, and “equivalent noise pressure” with
“equivalent bandwidth noise pressure”.]
3.6
electrical impedance
Z
complex valued quantity, the modulus of which is the ratio of the root-
mean-square voltage applied across the electrical terminals of a hydrophone to the resulting
root-mean-square current, and the argument of which is the phase difference between voltage
and current, at a specified frequency
Note 1 to entry: Electrical impedance of a hydrophone is expressed in ohm, Ω.
Note 2 to entry: Because the electrical impedance depends on the hydrostatic pressure, water temperature and
the length of the cable attached to the hydrophone, these parameters, as well as the frequency and the electrical
terminals where the electrical impedance is measured, should be specified.
3.7
electrical terminals
terminals across which the open-circuit voltage of a hydrophone is
measured
3.8
end-of-cable
specification that relates to the end of the integral cable of a hydrophone with or without an
integral pre-amplifier
Note 1 to entry: If the hydrophone is not provided with an integral cable, the specification relates to the output
connector firmly connected with the hydrophone, not any additional extension cable.
[SOURCE: IEC 62127-3:2007 [2], 3.4, modified – Replace “integral output cable if the
hydrophone or hydrophone assembly is provided with such a cable; if the hydrophone or
hydrophone assembly is not provided with an integral output cable, the specification relates to
the output connector firmly connected with the hydrophone or hydrophone assembly, not to an
extra cable” with “integral cable of a hydrophone with or without an integral pre-amplifier”. Add
Note 1 to entry.]
3.9
end-of-cable leakage resistance
R
L
ratio of the root-mean-square voltage across the end-of-cable electrical terminals of a
hydrophone to the direct root-mean-square current flowing through these terminals
Note 1 to entry: End-of-cable leakage resistance is expressed in ohm, Ω.
Note 2 to entry: The value of the voltage used during the determination of the end-of-cable leakage resistance
should be stated.
– 8 – IEC 60500:2017 © IEC 2017
[SOURCE: IEC 60866:1987 [3], 3.13, modified – Replace “voltage across the electrical
terminals at the end of the hydrophone cable to the direct current” with “root-mean-square
voltage across the end-of-cable electrical terminals of a hydrophone to the direct root-mean-
square current”.]
3.10
equivalent bandwidth noise pressure
p
W
ratio of the root-mean-square noise voltage in the relevant frequency band present at the
electrical terminals of the hydrophone, in the absence of sound pressure or pressure
fluctuations at the hydrophone input, to its sensitivity in a specified frequency band
Note 1 to entry: Equivalent bandwidth noise pressure is expressed in pascal, Pa.
3.11
equivalent noise pressure spectral density
p
s
equivalent bandwidth noise pressure when its bandwidth is 1 Hz
Note 1 to entry: Equivalent noise pressure spectral density is expressed in pascal per square root of hertz,
-1/2
Pa ⋅ Hz .
3.12
equivalent noise pressure spectral density level
twenty times the logarithm to the base 10 of the ratio of the equivalent noise pressure spectral
density of a hydrophone, p , to a reference pressure spectral density, p
s s0
Note 1 to entry: Equivalent noise pressure spectral density level of a hydrophone is expressed in decibel, dB.
-1/2
Note 2 to entry: The value of reference pressure spectral density, p , is 1 µPa ⋅ Hz .
s0
3.13
free field
sound field in a homogeneous and isotropic medium in which the effects of the boundaries are
negligible
[SOURCE: IEC 60565:2006 [1], 3.13]
3.14
free-field open-circuit complex sensitivity
M
f
complex valued quantity, the modulus of which is the free-field open-circuit sensitivity and the
argument of which is the sensitivity phase angle, for specified frequency and specified
direction of sound incidence at the position of the reference centre of the hydrophone if the
hydrophone was removed from the sound field
3.15
free-field open-circuit sensitivity
M
f
modulus of the free-field open-circuit complex sensitivity, which is equal to the ratio of the
open-circuit root-mean-square voltage at the end-of-cable of a hydrophone to the root-mean-
square sound pressure for specified frequency and specified direction of plane wave sound
incident on the position of the reference centre of the hydrophone in the undisturbed free field
if the hydrophone was removed
Note 1 to entry: Free-field open-circuit sensitivity is expressed in volt per pascal, V/Pa.
Note 2 to entry: The term ‘response’ is sometimes used instead of ‘sensitivity’.

3.16
free-field open-circuit sensitivity level
twenty times the logarithm to the base 10 of the ratio of the free-field open-circuit sensitivity,
M , to a reference sensitivity, M
f ref
Note 1 to entry: Free-field open-circuit sensitivity level is expressed in decibel, dB.
Note 2 to entry: The value of reference sensitivity, M , is 1 V/µPa.
ref
3.17
hydrophone
electroacoustic transducer that produces electrical signals in response to water borne
pressure signals
Note 1 to entry: A hydrophone is designed to respond principally to underwater sound pressure.
Note 2 to entry: In general, a hydrophone may also produce a signal in response to non-acoustic pressure
fluctuations (for example, those existing in a turbulent boundary layer during conditions of high water flow).
Note 3 to entry: Hydrophone types include reference hydrophones and measuring hydrophones. Measuring
hydrophones are used in general measurements of sound fields, and reference hydrophones are principally used
for calibration purposes (for example in comparison calibrations with measuring hydrophones).
Note 4 to entry: Hydrophones are principally used for listening devices, but in reciprocity calibration, a
hydrophone is used as reciprocal transducer, not only acting as a hydrophone, but also as a projector (sound
source).
Note 5 to entry: A hydrophone which is integrated with a digital acquisition system is sometimes termed a “digital
hydrophone”, but the combination is best considered as a measuring system, not a hydrophone alone.
Note 6 to entry: If a hydrophone is connected to a charge amplifier, the sensitivity of the hydrophone is
sometimes described in terms of charge sensitivity, which is related to the voltage sensitivity of the hydrophone by
its electrical capacitance.
[SOURCE: IEC 60565:2006 [1], 3.16, modified – Replace “transducer” with “electroacoustic
transducer”, and “water borne acoustic signals” with “water borne pressure signals”. Replace
the note with Notes 1 to 6 to entry.]
3.18
open-circuit voltage
U
H
voltage appearing at the electrical terminals of a hydrophone when no current passes through
the terminals
Note 1 to entry: Open-circuit voltage at hydrophone is expressed in volt, V.
[SOURCE: IEC 60565:2006 [1], 3.19, modified – Delete "at hydrophone" from the term.]
3.19
overload sound pressure
p
o
ratio of the maximum root-mean-square sound pressure applied at the hydrophone to cause a
distorted voltage output with specified criteria (linearity) to a reference sound pressure at a
specified frequency
Note 1 to entry: Overload sound pressure is expressed in pascal, Pa.
Note 2 to entry: The distortion tolerance criteria should be specified.
3.20
overload sound pressure level
twenty times the logarithm to the base 10 of the ratio of the overload sound pressure, p , to a
o
reference sound pressure, p
o0
Note 1 to entry: Overload sound pressure level is expressed in decibel, dB.

– 10 – IEC 60500:2017 © IEC 2017
Note 2 to entry: The value of reference sound pressure, p , is 1 µPa.
o0
3.21
phase angle
argument of the free-field open-circuit complex sensitivity, which is equal to the phase
difference between open-circuit voltage at the end-of-cable of a hydrophone and sound
pressure for specified frequency and specified direction of plane-wave sound incident on the
position of the reference centre of the hydrophone in the undisturbed free field if the
hydrophone was removed
3.22
pre-amplifier
active electronic device, often integrated into a particular hydrophone design, reducing the
hydrophone output impedance and amplifying the hydrophone output signal
Note 1 to entry: A pre-amplifier requires an electrical power supply voltage.
Note 2 to entry: The pre-amplifier may have a forward voltage transmission factor of less than one, i.e. it need not
necessarily be a voltage amplifier in the strict sense.
Note 3 to entry: If a differential amplifier is used as the pre-amplifier, its gain is usually termed a differential
output gain, and this will be a factor of 2 higher than for an equivalent single-ended pre-amplifier (6 dB increase in
level). The sensitivity of the hydrophone and pre-amplifier combination is then termed the differential output
sensitivity.
[SOURCE: IEC 62127-3:2007 [2], 3.12, modified – Delete "hydrophone" from the term.
Replace “connected to, or to be connected to, a particular hydrophone” with “, often integrated
into a particular hydrophone design,”, and add “and amplifying the hydrophone output signal”.
Replace the notes with Notes 1 to 3 to entry.]
3.23
pressure sensitivity
M
p
ratio of the root-mean-square output voltage to the root-mean-square
sound pressure averaged over the active element of the hydrophone designed to receive
sound, at a specified frequency
Note 1 to entry: Pressure sensitivity of a hydrophone is expressed in volt per pascal, V/Pa.
Note 2 to entry: The term ‘response’ is sometimes used instead of ‘sensitivity’.
[SOURCE: IEC 60565:2006 [1], 3.22, modified – Replace “output voltage” with “root-mean-
square output voltage”, “actual sound pressure existing over the region of hydrophone” with
“root-mean-square sound pressure averaged over the active element of the hydrophone”, and
add “at a specified frequency”. Replace the notes with Notes 1 and 2 to entry.]
3.24
pressure sensitivity level
twenty times the logarithm to the base 10 of the ratio of the pressure sensitivity, M , to a
p
reference sensitivity of M
ref
Note 1 to entry: Pressure sensitivity level is expressed in decibel, dB.
Note 2 to entry: The value of reference sensitivity M is 1V/µPa.
ref
[SOURCE: IEC 60565:2006 [1], 3.21].
3.25
principal axis
reference direction serving as an origin for the angular co-ordinate system used in describing
the directional characteristics of the hydrophone

Note 1 to entry: Generally, the axis of structural symmetry or the direction of maximum response is chosen for the
principal axis. See Figure 1 for description of angular co-ordinate system.
Note 2 to entry: The direction of maximum response may vary with the frequency of the sound.
[SOURCE: IEC 60565:2006 [1], 3.23, modified – Replace “transducer” with “hydrophone”.]
3.26
reference centre
point on, within or near a hydrophone about which its geometrical electroacoustic
characteristics are defined
Note 1 to entry: The reference centre often corresponds to the geometrical centre of a hydrophone, unless
otherwise stated.
[SOURCE: IEC 60565:2006 [1], 3.25, modified – Replace “point on or near a transducer” with
“point on, within or near a hydrophone”, and “acoustic receiving sensitivity and transmitting
responses” with “geometrical electroacoustic characteristics”. Replace note with Note 1 to
entry.]
3.27
sound pressure
p
difference between total pressure and pressure that would exist in the absence of sound
Note 1 to entry: Sound pressure is expressed in pascal, Pa.
Note 2 to entry: This definition follows the convention adopted with ISO for the definition of sound pressure such
that it is an instantaneous quantity. Note that in IEC 60050-801-21 [4] (IEV), this term is called “instantaneous
sound pressure”. In this document, where the root-mean-square sound pressure is intended, this is explicitly
referred to as “root-mean-square sound pressure”.
Note 3 to entry: See also ISO 80000-8:2007 [5], 8.9.2.
[SOURCE: ISO 18405:— [6], 2.1.2.1]
3.28
uncertainty
parameter, associated with the result of a measurement, that
characterizes the dispersion of the values that could reasonably be attributed to the
measurand
[SOURCE: ISO/IEC Guide 98-3:2008 [7], 2.2.3]
4 Symbols
C end-of-cable capacitance
H
f frequency
M free-field open-circuit complex sensitivity
f
M free-field open-circuit sensitivity
f
M pressure sensitivity
p
p sound pressure
p overload sound pressure
o
___________
Under preparation. Stage at the time of publication: ISO/DIS 18405:2016.

– 12 – IEC 60500:2017 © IEC 2017
equivalent bandwidth noise pressure
p
w
p equivalent noise pressure spectral density
s
R end-of-cable leakage resistance
L
U open-circuit voltage
H
Z electrical impedance
5 Hydrophone characteristics
5.1 General
The hydrophones used in underwater acoustics shall be generally of the piezoelectric type,
with or without an integral pre-amplifier. In order to fully characterize the performance of a
hydrophone, the information given in 5.2 to 5.10 is required. The recommended information to
be supplied by the manufacturer is simply summarized in Clause 6.
5.2 Basic requirements
The following shall be briefly stated:
• the basic physical principle of the transduction process;
• the type of element material, its form and the element size;
• the electrical capacitance of the sensor element;
• the type, configuration and overall size of the hydrophone;
• for a hydrophone with pre-amplifier, a simple circuit diagram, supply power requirements
and the connections of the pre-amplifier shall be given;
• the position of the reference centre of the hydrophone element within the overall
hydrophone body (important for phase measurement considerations);
• the calibrated directional response of a hydrophone;
• the frequency of the fundamental resonance of the hydrophone sensor element;
• the cable length of the hydrophone;
• the mass with or without cable;
• the serial number and the manufacturer’s model number;
• the hydrophone sensitivity, including any frequency dependence over the operating
frequency range.
If phase information is required, the sensitivity phase angle (which equals the argument of the
complex sensitivity) shall be stated in addition to the sensitivity magnitude (which equals the
modulus of the complex sensitivity), as well as the frequency dependence of the phase angle.
5.3 Sensitivity
The sensitivity of a hydrophone shall be expressed in S.I. units of volts per pascal (V/Pa) or
any allowed sub-multiple within the S.I. convention. It shall be stated whether the sensitivity
value given is understood as the free-field open-circuit sensitivity or the pressure sensitivity.
The uncertainty of the stated sensitivity shall be given.
For a hydrophone with pre-amplifier, the gain of the pre-amplifier with the frequency
dependence shall be stated.
The sensitivity level of the hydrophone shall be expressed in decibels, and the reference
value of sensitivity shall be given.
The frequency or frequency interval over which the sensitivity is applicable shall be stated.
The methods by which the sensitivity and its uncertainty have been obtained shall be
described.
A recommended calibration period shall be provided in the instructions for use. This
recommendation shall be followed, unless otherwise stated by specific device application
standards.
A calibration period of one year will be appropriate in most cases. However, if a hydrophone
is used in an application in which the hydrophone is susceptible to damage, the calibration
period should be less than one year.
NOTE The value of reference sensitivity in the calculation of the sensitivity level is 1 V/µPa.
5.4 Frequency response
5.4.1 Stated operating frequency band
The operating frequency band claimed for the hydrophone shall be stated by giving the lower
frequency limit and the upper frequency limit. The sensitivity of the hydrophone shall be
uniform over the stated frequency band, with a tolerance which shall also be stated.
5.4.2 Frequency dependence
The sensitivity or sensitivity level of the hydrophone as a function of frequency shall be stated
either graphically or as a list of values and over a frequency range containing at least the
frequency band claimed under 5.4.1. If it is given as a list of values or as discrete points in a
graph, the frequency interval between adjacent points shall be narrow enough that all
important details of the frequency dependence are shown, and the sensitivity level does not
vary by more than ±1 dB between adjacent points.
If the sensitivity response is given as a list of absolute sensitivity values, the sensitivity
statement in accordance with 5.3 may be omitted.
NOTE 1 The frequency response may depend on the electrical loading conditions.
NOTE 2 If, in a practical application, the hydrophone is used with subsequent electronic components such as an
amplifier, digitizer, etc., the frequency response of the whole system will also be influenced by the frequency
response of these additional components [8, 9].
5.5 Directional response
Usually, the directional response of the hydrophone is stated at the four highest preferred
frequencies of the specified frequency range claimed under 5.4.1 in accordance with ISO 266.
The directional response close to the fundamental resonance shall also be stated if this
resonance is inside the claimed operating frequency band. The method used to determine the
directional response shall be stated.
Each of the resulting directional responses obtained from the measurements shall be stated.
5.6 Dynamic range
5.6.1 Linearity and overload sound pressure level
The linear range of the hydrophone shall be stated, i.e. the sound pressure range in which the
hydrophone behaves in a linear way according to the condition below.

– 14 – IEC 60500:2017 © IEC 2017
The condition is as follows: If, on a plot of end-of-cable output voltage against sound pressure,
a straight line can be drawn through the origin in such a way that over a certain sound
pressure range the actual voltage values do not deviate from linear dependence to within
specified tolerance criteria, this range is the linear range of the hydrophone. Otherwise, the
sound pressure level when the actual voltage value deviates from the straight line by the
specified tolerance criteria is termed the overload sound pressure level. This shall be the
case for any frequency within the frequency band claimed under 5.4.1.
The tolerance criteria for the linearity should be specified.
5.6.2 Equivalent noise pressure spectral density level
The value of equivalent noise pressure spectral density level of the hydrophone shall be
stated.
NOTE 1 Usually, the equivalent noise pressure spectral density level of a hydrophone depends on the electronic
noise level across the electrical terminals of the pre-amplifier and the sensitivity of the hydrophone.
NOTE 2 The requirement of equivalent noise pressure spectral density level depends on the environment where
the hydrophone is used [10, 11].
5.6.3 Conditions required
The dynamic range of the hydrophone is usually expressed in decibels. The dynamic pressure
range in which the hydrophone can be used shall meet at least the following conditions:
• no mechanical or electrical damage to the hydrophone;
• no output saturation – the output signal shall be below the value corresponding to the
overload sound pressure level;
• the output signal shall be above the value corresponding to equivalent noise pressure
spectral density level.
NOTE “Output saturation” means that a non-zero pressure increment at the hydrophone does not lead to a
voltage change.
5.7 Electrical requirements
5.7.1 Electromagnetic interference
Information or advice on how to minimize the effects of electromagnetic interference shall be
provided. The design of the structure and the electrical circuit of the hydrophone shall be
considered to minimize the effect of electrical cross-talk interference.
5.7.2 Electrical characteristics
For hydrophones with an integral pre-amplifier, exposed metal parts of the hydrophone
housing and electrostatic shield shall be connected to the cable screen. For a hydrophone
without pre-amplifier, exposed metal parts and electrostatic shield shall not be connected to
the cable screen, and the end-of-cable leakage resistance shall be greater than 100 MΩ in the
frequency range 1 Hz to 100 kHz; at frequencies higher than 100 kHz, the end-of-cable
leakage resistance shall be greater than 100 kΩ.
NOTE Usually, the voltage applied to measure the end-of-cable leakage resistance is 100 V.
5.8 Mechanical requirements
The types of material (which may include metal, rubber, casting resin, polyurethane
encapsulating boot) exposed to the liquid in which the hydrophone is allowed to be used shall
be stated.
For a hydrophone filled with oil, the type of oil used shall be stated, and its acoustic
impedance shall be close to that of water.

All exposed parts of a hydrophone should be made from corrosion-compatible and corrosion-
resistant materials, and have characteristics of good wetting and small acoustic scattering. In
particular, the use of a variety of different metals for exposed components should be avoided
to avert the possible occurrence of galvanic corrosion, and promote long-term stability of
characteristics.
Correct suspension of the sensor element should be achieved to militate against induced
vibration, and the size should not be too large in relation to the acoustic wavelength.
5.9 Environmental aspects
The temperature of the water may affect the sensitivity of a hydrophone. High stresses
developed during deep submergence may change the sensitivity of a piezoelectric ceramic
element permanently [12, 13]. This means that a hydrophone will have limitations for its
operating temperature and depth [14, 15].
The permitted operating temperature range, storage temperature range and maximum
operating depth for the hydrophone shall be stated.
Exposure to sunlight, chemicals, ionizing radiation and mechanical shock may affect the
operational characteristics of the hydrophone. Advice or guidance on how to use and store the
hydrophones to avoid these deleterious effects shall be given.
5.10 Stability of the sensitivity
5.10.1 Temperature stability
The temperature coefficient of sensitivity and the frequency
...