SIST EN 61043:2000

SLOVENSKI STANDARD
SIST EN 61043:2000
01-december-2000
Electroacoustics - Instruments for the measurement of sound intensity -
Measurement with pairs of pressure sensing microphones
Electroacoustics - Instruments for the measurement of sound intensity - Measurement
with pairs of pressure sensing microphones
Elektroakustik - Geräte für die Messung der Schallintensität - Messungen mit Paaren von
Druckmikrofonen
Electroacoustique - Instruments pour la mesure de l'intensité acoustique - Mesure au
moyen d'une paire de microphones de pression
Ta slovenski standard je istoveten z: EN 61043:1994
ICS:
17.140.50 Elektroakustika Electroacoustics
SIST EN 61043:2000 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 61043:2000

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SIST EN 61043:2000

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SIST EN 61043:2000

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SIST EN 61043:2000

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SIST EN 61043:2000

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SIST EN 61043:2000
NORME
CEI
INTERNATIONALE IEC
1043
INTERNATIONAL
Première édition
STANDARD
First edition
1993-12
Electroacoustique — Instruments pour la mesure
de l'intensité acoustique — Mesure au moyen
d'une paire de microphones de pression
Electroacoustics — Instruments for the
measurement of sound intensity —
Measurement with pairs of pressure
sensing microphones
© CEI 1993 Droits de reproduction réservés — Copyright — all rights reserved
Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in
utilisée sous quelque forme que ce soit et par aucun pro- any form or by any means, electronic or mechanical,
cédé, électronique ou mécanique, y compris la photocopie et including photocopying and microfilm, without permission
les microfilms, sans l'accord écrit de l'éditeur in writing from the publisher.
Bureau Central de la Commission Electrotechnique Internationale 3, rue de Varembe Genève, Suisse
Commission Electrotechnique Internationale CODE PRIX "
International Electrotechnical Commission PRICE CODE V
Meie yHapoAHaa 3netmporexuHueasaa HoMHCCHR
IEC
Pour prix, voir catalogue en vigueur
•
For price, see current catalogue

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SIST EN 61043:2000
1043 ©IEC:1993 — 3 —
CONTENTS
Page
FOREWORD 7
INTRODUCTION 9
Clause
1 Scope 11
2 Normative references 11
Definitions
3 13
4 Grades of accuracy 17
5 Reference environmental conditions 19
6 Sound intensity processors: requirements 19
6.1 Frequency range 19
6.2 Filtering 19
6.3 A-weighting 19
6.4 Indicator accuracy 21
6.5 Provision for microphone separation 21
6.6 Presentation of results 21
6.7 Time averaging 21
6.8 Crest factor handling 23
6.9 Pressure-residual intensity index 23
6.10 Provision for phase compensation 23
6.11 Provision for range setting 23
6.12 Provision for overload indication 25
6.13 Provision for corrections for atmospheric pressure and temperature 25
6.14 Operating environment 25
7 Sound intensity probes: requirements 25
7.1 Mechanical construction 25
7.2 Response to sound pressure 27
7.3 Response to sound intensity 27
7.4 Directional response characteristics 29
7.5 Pe rformance in a standing wave field 31
7.6 Pressure-residual intensity index 31
7.7 Environmental conditions 33
8 Sound intensity instruments: requirements 33
9 Power supplies: requirements 33

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SIST EN 61043:2000
1043 ©IEC:1993 – 5
Clause Page
10 Sound intensity probe calibrators: requirements 33
10.1 Sound pressure calibrators 33
10.2 Residual intensity testing devices 33
10.3 Sound intensity calibrators 35
11 Sound intensity processors: performance verification 35
11.1 Octave and one-third octave filters 35
11.2 Sound intensity indication 37
11.3 Time averaging 37
11.4 Crest factor handling 39
11.5 Pressure-residual intensity index and operating range 39
12 Sound intensity probes: performance verification 41
12.1 Frequency response 41
12.2 Directional response 43
12.3 Performance in a standing wave field 43
12.4 Pressure-residual intensity index 43
13 Calibrators: performance verification 45
13.1 Sound pressure calibrators 45
13.2 Residual intensity testing devices 45
13.3 Sound intensity calibrators 45
14 Field calibration and checks 47
15 Marking and instruction manuals 49
15.1 Marking 49
15.2 Instruction manuals 49
Annexes
A Periodic verification procedures 53
B Sound intensity processors employing autoranging 57
C Sound intensity processors based on DFT analysers converting narrow bands
to one-octave or one-third octave 59
D
RC networks for generating known phase shifts 65
E Dynamic capability index 67

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SIST EN 61043:2000
1043 ©I EC:1993 - 7 -
INTERNATIONAL ELECTROTECHNICAL COMMISSION
ELECTROACOUSTICS -
INSTRUMENTS FOR THE MEASUREMENT OF SOUND INTENSITY -
MEASUREMENT WITH PAIRS OF PRESSURE SENSING MICROPHONES
FOREWORD
1)
The IEC (International Electrotechnical Commission) is a worldwide organization for standardization
comprising all national electrotechnical committees (IEC National Committees). The object of the IEC is to
promote international cooperation on all questions concerning standardization in the electrical and
electronic fields. To this end and in addition to other activities, the IEC publishes International Standards.
Their preparation is entrusted to technical committees; any IEC National Committee interested in
the subject dealt with may participate in this preparatory work. International, governmental and
non-governmental organizations liaising with the IEC also participate in this preparation. The IEC
collaborates closely with the International Organization for Standardization (ISO) in accordance with
conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of the IEC on technical matters, prepared by technical committees on
which all the National Committees having a special interest therein are represented, express, as nearly as
possible, an international consensus of opinion on the subjects dealt with.
3) They have the form of recommendations for international use 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.
International Standard IEC 1043 has been prepared by IEC technical committee 29:
Electroacoustics.
This standard completes the series of International Standards already prepared or in
preparation by subcommittee 1 of ISO committee 43: Acoustics/noise, ISO/TC 43/SC1.
The text of this standard is based on the following documents:
Six Months' Rule Report on Voting
29(CO)185 29(CO)211
Full information on the voting for the approval of this standard can be found in the repo rt
on voting indicated in the above table.
Annex A forms an integral pa rt of this standard.
Annexes B, C, D and E are for information only.

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SIST EN 61043:2000
1043 ©IEC:1993 - 9 -
INTRODUCTION
This International Standard specifies the requirements for sound intensity instruments,
comprising sound intensity probes and processors, which detect sound intensity by pairs
of spatially separated pressure sensing microphones. These instruments, and others
employing different detection methods, are still the subject of development.
Sound intensity instruments have two main applications. The first is the investigation of
the radiation characteristics of sound sources. The second is the determination of the
sound power of sources, especially in situ, where sound intensity measurement enables
sound power determination to be made under acoustical conditions which render determi-
nation by sound pressure measurement impossible.
This International Standard applies to instruments to be used for the determination of
sound power in accordance with the requirements of ISO 9614-1 and ensures well-defined
performance for instruments used in other applications.
Specifications and tolerances are based on current instrument technology and on typical
industrial requirements for dynamic capability index.
Requirements for the verification of pe rformance of probes and processors are written in
terms of type tests. A scheme for periodic verification, serving as the basis of the periodic
recalibrations required in many countries, is given in annex A.
Probes and processors are treated separately and together; in the latter case they are
called "instruments".

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SIST EN 61043:2000
1043 ©IEC:1993 -11 -
ELECTROACOUSTICS -
INSTRUMENTS FOR THE MEASUREMENT OF SOUND INTENSITY -
MEASUREMENT WITH PAIRS OF PRESSURE SENSING MICROPHONES
1 Scope
The primary purpose of this Standard is to ensure the accuracy of measurements of sound
intensity applied to the determination of sound power in accordance with ISO 9614-1.
To meet the requirements of that standard, instruments are required to analyse the sound
intensity in one-third octave or octave bands, and optionally to provide A-weighted band
levels. They are also required to measure sound pressure level in addition to sound
intensity level to facilitate the use of the field indicators described in ISO 9614-1.
This International Standard only applies to instruments which detect sound intensity by
pairs of spatially separated pressure sensing microphones.
This International Standard specifies performance requirements for instruments used for
the measurement of sound intensity, and their associated calibrators.
The requirements are intended to reduce to a practical minimum any differences in equi-
valent measurements made using different instruments, including instruments comprising
probes and processors from different manufacturers.
2 Normative references
The following normative documents contain provisions which, through reference in this
text, constitute provisions of this International Standard. At the time of publication, the
editions indicated were valid. All normative documents are subject to revision, and parties
to agreements based on this International Standard are encouraged to investigate the
possibility of applying the most recent editions of the normative documents listed below.
Members of IEC and ISO maintain registers of currently valid International Standards.
ISO 9614-1: 1993,
Acoustics - Determination of sound power levels of noise sources
using sound intensity - Part 1: Measurement at discrete points
IEC 651: 1979, Sound level meters
IEC 942: 1988, Sound calibrators
IEC 1260: 19XX, Specification for octave-band and fractional octave-band filters
(under
consideration). (Revision of IEC 225: 1966)

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1043 ©IEC:1993 - 13 -
Definitions
3
For the purpose of this International Standard, the following definitions apply.
3.1 sound intensity probe:
Transducer system from which signals may be processed
to obtain the sound intensity component in a specific direction.
3.2 p-p probe (also known as a two
microphone probe): Probe composed of two
pressure sensing microphones spaced apart by a fixed and known distance, in which the
sound pressure component is measured by the two microphones and the mean value is
considered as the sound pressure existing at the reference point of the probe, while the
sound pressure differential is used for the purpose of deriving the sound particle velocity
component.
NOTES
1 A side-by-side p-p probe has the two microphones arranged as shown in figuret.
2 A face-to-face p-p probe has the two microphones facing each other and separated by a spacer as
shown in figure 2.
lEC 1232/93
1EC 1231/93
Figure 1 - A side-by-side p-p probe Figure 2 -A face-to-face p-p probe
3.3 reference point of a probe:
Point at which the sound intensity is deemed to be
measured.
NOTE — The reference point of a probe is not necessarily the physical midpoint, but occurs halfway
between the effective microphone centres.
3.4 probe axis: Axis passing through the reference point and along which a component
of particle velocity is sensed.
3.5 reference direction:
Direction of incidence of plane progressive waves on the
probe, parallel to the probe axis, for which the sound intensity response of the probe is
specified.

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SIST EN 61043:2000
1043 ©IEC:1993 - 15 -
3.6 phase difference between probe channels for a p-p probe: Difference in phase
response between the channels in a p-p probe, including microphones, preamplifiers and
cables, if they are an integral part of the probe, when subjected to the same input. It is a
function of frequency.
3.7 nominal separation of microphones in a p-p probe: Fixed value of separation
used for the purpose of computing sound intensity directly in an instrument. It is the mean
value of the effective separation of the microphones in a specified frequency range.
3.8 sound intensity processor:
Device whose function is the determination of sound
intensity in conjunction with a specified probe. The processor presents results in one
octave or one-third octave bands, in terms of sound intensity and sound pressure, or
sound intensity level and sound pressure level.
3.9 sound intensity instrument: Comprises a sound intensity probe and a compatible
sound intensity processor.
3.10 residual intensity: False intensity produced by phase differences between
measurement channels, which occurs when the processor is subjected to identical elec-
trical inputs to the two channels, or when the transducers in the probe connected to the
processor are subjected to identical sound pressure inputs.
3.11 pressure-residual intensity index: Difference between the indicated sound
pressure levels and the indicated residual intensity levels, calculated with air density of
1,2048 kg/m3, in one octave or one-third octave bands, when the processor is subjected to
identical electrical pink noise inputs to the two channels, or when the transducers
connected to the inputs are subjected to identical pink noise sound pressure inputs. This
index applies only where it is essentially independent of indicated sound pressure level.
3.12 dynamic capability index: Difference between pressure-residual intensity index
found in an instrument and K factor, described as bias error factor, in ISO 9614. It signi-
fies the maximum difference between sound pressure level and sound intensity level
within which measurements according to ISO 9614 can be made for different grades of
measurement accuracy.
3.13 operating range: Range of sound pressure levels, in decibels, between the highest
and lowest levels of pink noise indicated by a processor or instrument, within which the
pressure-residual intensity index meets the requirements of this standard.
3.14 electrostatic actuator: Device used for electrical measurements of the frequency
response of condenser microphones. It is a metallic grid which is held close and parallel to
the microphone diaphragm. An alternating test voltage, normally superimposed on a high
static voltage, is applied between the actuator and the diaphragm. The resulting electro-
static forces mimic the effect of a sound pressure on the microphone.
3.15 real time operation: Mode of operation of a processor such that all pertinent data
appearing at inputs within the total averaging time are used in computing sound pressure
and sound intensity.

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SIST EN 61043:2000
1043 © IEC:1993 - 17 -
NOTE – Depending upon particular characteristics of the processor, even in real time operation some
pertinent data can be effectively lost or not fully taken into account, as described in annex C.
3.16 phase difference compensation:
Function provided in some processors which, by
applying corrections for phase difference, offers an increase in the pressure-residual inten-
sity index found during the process of calibration.
NOTE – Application of this function does not reduce the component of residual intensity caused by elec-
trical noise.
3.17 autoranging: Function provided in some processors which automatically selects
the optimum range for accuracy, linearity and pressure-residual intensity index.
NOTE – The use of an autoranging function is described in annex B.
3.18 sound pressure calibrator: Calibrator suitable for the pressure calibration of
microphones or sound pressure measuring/analysing channels in a sound intensity instru-
ment.
3.19 residual intensity testing device: Device which, by application of identical sound
pressure simultaneously to the microphones of a p-p probe, allows direct computation of
pressure-residual intensity index in a frequency band and at one or more sound pressure
levels.
3.20 sound intensity calibrator: Calibrator which allows direct calibration of the sound
intensity indication of an instrument.
3.21 type test: Examination of one or more measuring instruments or transducers of the
same type which are submitted to a national service of legal metrology; this examination
includes the tests necessary for the approval of the type.
3.22 verification: All the operations carried out by an organ of the national service of
legal metrology (or other legally authorized organisation) having the object of ascertaining
and confirming that the measuring instrument entirely satisfies the requirements of the
regulations for verification.
3.23 initial verification: Verification of a measuring instrument which has not been
verified previously.
3.24 periodic
verification: Subsequent verification of a measuring instrument carried
out periodically at intervals and according to the procedures laid down by regulations.
4 Grades of accuracy
Instruments, processors and probes are classified according to the measurement accuracy
achieved. There are two degrees of accuracy, designated as class 1 and class 2. The
same requirements apply to both classes, the differences are only in the tolerances
allowed, and in pressure-residual intensity indices, where class 2 requirements are less
stringent than those for class 1.
There is an additional class, designated as 2X, which applies to processors and instru-

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SIST EN 61043:2000
1043 ©
IEC:1993 - 19 -
ments which, in the frequency range required in this standard, do not operate in real time.
5
Reference environmental conditions
The reference environmental conditions are:
- Temperature 20 °C
- Static pressure 101,325 kPa
-
Relative humidity 65 %
NOTE - The difference between the sound pressure level and sound intensity level in a plane progressive
wave is given by
Li = LP+ 10Ig ( P^) dB
where
p is the density of the air, in kilogrammes per cubic metre;
c is the speed of sound, in metres per second.
At reference environmental conditions this relationship is L i = Lp - 0,15 dB.
6 Sound intensity processors: requirements
6.1 Frequency range
Class 1 processors shall, at least, cover the range from 45 Hz to 7,1 kHz in one-third
octave bands. Class 2 processors shall, at least, cover the range from 45 Hz to 7,1 kHz in
one-third octave bands, or the range from 45 Hz to 5,6 kHz in one octave bands.
6.2 Filtering
Filtering shall be in accordance with the requirements of table 1. Filters may be analogue
or digital, or bands may be synthesized from narrower band analysis and shall meet the
requirements of IEC 1260 (under consideration).
Processors class 1 and 2 shall operate in real time. Overlap signal processing (see
annex C) is required for Fast Fourier Transform (FFT) analysers.
Processors not operating in real time shall be classified as class 2X and meet the require-
ments specified in table 1.
6.3 A-weighting
Processors may provide A-weighted octave and one-third octave band results. The weight-
ing shall be in accordance with the requirements of IEC 651. The tolerance on
the weighting shall be 0,5 times the tolerance limits given for a type 1 sound level meter in
table V of IEC 651.

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SIST EN 61043:2000
1043 © IEC:1993
-21 -
Table 1 - Specification and performance requirements for sound intensity processors
Class 1 Class 2
Class 2X
Filter type
One-third octave Octave or one-third octave Octave or one-third octave
IEC 1260, Class 1 IEC 1260, Class 2 IEC 1260, Class 2
Real time signal processing Mandatory. Overlap processing required if bands are Full information required on
synthesized from FFT analysis.
time windows, data acquisi-
tion and processing time.
Indicator accuracy
±0,2 dB ±0,3 dB 1-0,3 dB
Microphone separation set- ±0,1 dB ±0,2 dB
±0,2 dB
ting accuracy
Time averaging
10 s – 180 s continuous or in 10 s –180 s continuous or in 30 s to 600 s
steps of 1 s or less steps
Provision for calculation of Mandatory Optional
Optional
sound intensity at ambient
conditions
6.4 Indicator accuracy
Sound intensity, or sound intensity level, shall be indicated with the accuracy given in
table 1.
6.5 Provision for microphone separation
Provision shall be made in the processors for direct computation of results according to
the nominal microphone separation used in the probe. It shall be possible to set the
nominal separation with sufficient precision to enable the calculation to be performed with
the accuracy given in table 1.
6.6 Presentation of results
The processor shall indicate or provide an output proportional to sound intensity and
sound pressure, or to sound intensity level and sound pressure level.
Processors shall offer a resolution of 0,1 dB.
A means of identifying positive and negative intensity shall be provided. It is recom-
mended that provision be made for the indication of the pressure-residual intensity index.
Provision for spectrum display and hard copy facilities are also recommended.
6.7 Time averaging
The processor shall provide the time averaged value of sound intensity. The integration
time shall be variable in the range, and with the resolution, given in table 1.

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SIST EN 61043:2000
1043 ©IEC:1993 – 23 –
6.8 Crest factor handling
The processor shall be capable of indicating correctly when signals with crest factors of up
to 5 (14 dB) are measured.
6.9 Pressure-residual intensity index
In the operating range, the processor shall have pressure-residual intensity index equal to,
or higher than, that shown in table 2.
6.10 Provision for phase compensation
Provision for phase compensation may be provided in a processor. If it is provided,
full information on its use and limitations shall be included in the instruction manual.
6.11 Provision for range setting
Range setting may be manual or autoranged. It shall be possible to lock any automatically
selected range independently of any other control function, except "reset".
Table 2 – Minimum pressure-residual intensity index requirements for probes,
processors and instruments for 25 mm nominal microphone separation
in decibels
Band centre Probe Processor Instrument
frequency
Hz Class 1 Class 2 Class 1 Class 2 Class 1 Class 2
50 13 7 19 13 12 6
63 14 8 20 14 13 7
80
15 9 21 15 14 8
100 16 10 22 16 15 9
125 17 11 23 17 16 10
160 18 12 24 18 17 11
200
19 13 25 19 18 12
250 20 14 26 20 19 13
315
20 15 26 20 19 14
400 20 16 26 20 19
14,5
500 20 17 26 20 19 15
630 20 18 26 20 19 16
800
20 18 26 20 19 16
1000 20 18 26 20 19
16
1 250 20 18 26 20 19 16
1 600 20 18 26 20 19 16
2 000
20 18 26 20 19 16
2 500 18 26
20 20 19 16
3 150 20 18 26 20 19 16
4 000 20 18 26 19
20 16
5 000 20 18 26 20 19 16
6 300
20 18 26 20 19 16
NOTES
1 For pressure-residual intensity requirements for microphone separations other than 25 mm, add
10 Ig (x/25) where x is the microphone separation in millimetres, to the figures, in decibels, in the table.

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SIST EN 61043:2000
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2 For processors with only octave analysis, the requirements apply only at the octave band centre
frequencies.
6.12 Provision for overload indication
Processors shall be equipped with latching overload indicators. The indication shall occur
when the input signals to the processor are too large for the processor to operate within
the requirements of this standard.
6.13 Provision for corrections for atmospheric pressure and temperature
Class 1 processors shall have provision for entering values of ambient atmospheric
pressure and temperature, or correction factors derived from these, for use in the calcu-
lation of sound intensity.
6.14 Operating environment
Processors shall meet the requirements of tablet in the ambient temperature range of
5 °C to 40 °C.
7 Sound Intensity probes: requirements
7.1 Mechanical. construction
Sound intensity probes shall be constructed to meet the requirements of this Standard
over at least three consecutive octave bands with the same microphones and the same
spacing.
When the full frequency range is covered by different probe configurations, each one
covering part of the whole range, a full octave band overlap is recommended.
The construction of the probes shall give mechanical stability, with a known and fixed
distance between the microphones.
Probes shall be constructed using pairs of microphones of the same type, which means
the same physical dimensions, the same polarization requirements, the same design, the
same temperature, humidity and ageing characteristics, and high phase stability.
Probes shall be marked to allow identification of the two channels so that the direction of
the intensity indicated by the processor can be correctly interpreted.
In probes in which transducers can be removed, transducers used in the probe shall have
identifying marks, e.g. serial numbers, so that (matched) pairs can be easily identified.
In all probes, provision shall be made for the application of a sound pressure calibrator
and a residual intensity testing device.

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SIST EN 61043:2000
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7.2
Response to sound pressure
For plane progressive waves incident on the probe in the reference direction, the indivi-
dual microphones located in the probe shall have frequency responses to sound pressure,
relative to the response at 250 Hz, within the tolerances given in table 3.
NOTE - Requirements are given for the response of the individual microphones, rather than a pressure
response of a probe, because the latter is dependant on the calculation method in a processor and cannot
be uniquely defined for a probe alone.
Table 3 - Tolerances for sound pressure and sound intensity response
Frequency Microphone response
Probe intensity response
Tolerance Tolerance Tolerance Tolerance Nominal for
Hz class 1 class 2 class 1
class 2 25 mm
separation
dB dB
dB dB dB
50 ±0,5 ±0,7 ±1,0 ±1,5
0,0
63 ±0,5
±0,7 ±1,0 ±1,4 0,0
80
±0,5 ±0,7 ±0,9 ±1,3 0,0
100 ±0,5 ±0,7
±0,8 ±1,2 0,0
125 ±0,5 ±0,7 ±0,7 ±1,1 0,0
160 ±0,5 ±0,7
±0,7 ±1,0 0,0
200 ±0,5 ±0,7 ±0,7 ±1,0 0,0
250 reference reference reference reference reference
315
±0,5 ±0,7 ±0,7 ±1,0 0,0
400 ±0,5 ±0,7 ±0,7 ±1,0
0,0
500
±0,5 ±0,7 ±0,7 ±1,0 0,0
630 ±0,5 ±0,7 ±0,7
±1,0 - 0,1
800
±0,5 ±0,7 ±0,7 ±1,0 - 0,1
1 000 ±0,5 ±0,7 ±0,7 ±1,0
- 0,1
1 250
±0,5 ±0,7 ±0,8 ±1,0 - 0,2
1 600 ±0,6 ±0,8 ±0,9 ±1,1 - 0,4
2 000
±0,7 ±1,0 ±1,0 ±1,3 - 0,6
2 500 ±0,8 ±1,2 ±1,1 ±1,6
- 1,0
3 150 ±0,9
±1,4 ±1,2 ±1,9 - 1,6
4 000 ±1,0 ±1,6 ±1,3 ±2,2 - 2,7
5 000 ±1,2
±1,8 ±1,6 ±2,5 - 4,8
6 300 ±1,4 ±2,0 ±1,9 ±2,8 - 10,5
NOTE - For nominal sound intensity response with microphone separations other than 25 mm, apply the
formula given in 7.3.
7.3 Response to sound intensity
For plane progressive waves incident in the reference direction, the probe shall be
capable of providing signals to a processor meeting class 1 accuracy requirements so that
intensity values may be computed in the processor resulting in an intensity response,
relative to that at a reference frequency of 250 Hz, by the following formula:
sin 0f
0ref
10 Ig
O Sin B
f ref

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SIST EN 61043:2000
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where
ef=drxfx2xn/c radians;
dr is the microphone separation, in metres
f is the frequency, in hertz
c is the speed of sound at reference conditions in metres per second (343,37)
isthe value of of at the reference frequency.
ref
A probe only meets the requirements of this standard in the frequency range where the
nominal response relative to 250 Hz is (0 ± 1) dB.
The response shall be within the tolerances given in table 3. Table 3 also gives the
nominal response of a probe with 25 mm microphone separation, calculated from the
above formula.
7.4 Directional response characteristics
The directional response characteristics are specified in three mutually perpendicular
planes XY, YZ and ZX, as shown in figures 3 and 4. The intensity response in the ZX and
ZY planes shall follow the cosine law over 360° from the reference direction.
The maximum positive response shall be at 0° and the maximum negative response (flow
opposite to reference direction) shall be at 180°.
The response at angles 270° < 4 < 90° shall be the
...