Electroacoustics - Instruments for the measurement of sound intensity - Measurement with pairs of pressure sensing microphones

Applies to instruments which detect sound intensity by pairs of spatially separated pressure sensing microphones and specifies performance requirements for instruments used for the measurement of sound intensity, and their associated calibrators. The 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. 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.

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

S'applique uniquement aux instruments qui mesurent l'intensité acoustique au moyen d'une paire de micropones de pression séparés dans l'espace et donne les prescriptions concernant les caractéristiques des instruments utilisés pour la mesure de l'intensité acoustique, ainsi que celles des calibbreurs associés. Le but de cette norme est d'assurer l'exactitude des mesures de l'intensité acoustique, appliquées à la détermination de la puissance acoustique, conformément à l'ISO 9614. Pour satisfaire aux prescriptions de l'ISO 9614, les instruments doivent analyser l'intensité acoustique en bandes d'octaves, ou de tiers d'octaves, et peuvent éventuellement indiquer des niveaux correspondant à la pondération fréquentielle A.

Electroacoustics - Instruments for the measurement of sound intensity - Measurement with pairs of pressure sensing microphones

General Information

Status
Published
Publication Date
30-Nov-2000
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
01-Dec-2000
Due Date
01-Dec-2000
Completion Date
01-Dec-2000

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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
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

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.

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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SIST EN 61043:2000
1043 ©IEC:1993 - 13 -
Definitions
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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1043 ©
IEC:1993 - 19 -

ments which, in the frequency range required in this standard, do not operate in real time.

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
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
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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1043 ©IEC:1993 - 25 -

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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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
±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
1043 ©IEC:1993 - 29 -
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
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