EN 61043:1994
(Main)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
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
Standards Content (Sample)
SLOVENSKI STANDARD
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
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
NORME
CEI
INTERNATIONALE IEC
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
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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
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
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.
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".
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)
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.
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.
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-
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.
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.
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
19 13 25 19 18 12
250 20 14 26 20 19 13
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
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.
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.
1043 ©I EC:1993 - 27 -
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
±0,5 ±0,7 ±0,7 ±1,0 0,0
400 ±0,5 ±0,7 ±0,7 ±1,0
0,0
±0,5 ±0,7 ±0,7 ±1,0 0,0
630 ±0,5 ±0,7 ±0,7
±1,0 - 0,1
±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
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 response at 0° plus 10 Ig(cos 4)) dB.
The response at angles 90° < 4) < 270° shall be the response at 180° plus 10 Ig (-cos 4)) dB.
The minimum response shall occur within ±5° for Class 1 and ±7° for Class 2 of 90° and
270°. The angle 4) is the angle between the direction of incidence and the probe axis in
the ZX and ZY planes.
±2
Tolerances shall be ±1,5 dB for a class 1 probe and dB for a class 2 probe within 60°
of the reference direction, i.e. within angles 300° - 0° - 60° and 120° - 180° - 240°.
NOTE — Requirements for responses at angles between 60° and 90° from the reference direction are not
given, due to difficulties in their verification.
1043 © IEC:1993
-31 -
1EC 1233193
Figure 3 - Axes for specifying the Figure 4 -Axes for specifying the
directional response of a
directional response of a
face to face p-p probe
side by side p-p probe
7.5 Performance in a standing wave field
Probes shall be constructed to ensure the correct measurement of sound intensity in
standing wave fields. Performance requirements are only specified in the low end of the
audio frequency range where low vent pressure attenuation and poor phase matching
between the microphones are known to lead to measurement errors. Errors due to the
probe sensing the pressure and particle velocity at different points will also be detected in
this frequency range.
In standing waves of 24 dB for class 1 probes and 20 dB for class 2 probes (difference
between pressure maxima and minima) generated in a duct or a tube, the intensity
measured with a probe shall be correct within +1,3 and - 1,75 dB for class 1 and within
+1,6 and -2,5 dB for class 2 probes. The tolerances apply at 125 Hz, or the lowest
specified frequency for the probe, if it falls between 125 Hz and 400 Hz.
NOTES
1 The correct value for the sound intensity level may be calculated by subtracting half the standing wave
ratio from the sound pressure level at a node in the standing wave field and applying the correction
between sound pressure level and sound intensity level given in clause 5 above.
2 To meet these requirements a probe may require a nominal microphone separation greater than the
25 mm used as an example in table 2.
7.6
Pressure-residual intensity index
Probes shall meet the requirements given in table 2.
1043 ©IEC:1993 - 33 -
7.7 Environmental conditions
Probe testing shall be done at reference environmental conditions, or as close to the refer-
ence environmental conditions as is practical. The actual environmental conditions during
the test shall be stated.
8 Sound intensity instruments: requirements
When a probe and processor are supplied together as an instrument of a specified class,
the resulting instrument shall perform at least as well as the combination of a probe and
processor, both of that same specified class.
When a probe and processor are supplied separately, a class 1 instrument shall consist of
a class 1 processor and a class 1 probe. A class 2 instrument shall consist of either
a class 1 processor and a class 2 probe, a class 2 processor and a class 1 probe, or a
class 2 processor and a class 2 probe. A class 2X instrument shall consist of either
a class 2X processor and a class 1 probe, or a class 2X processor and a class 2 probe.
9 Power supplies: requirements
Power supplies, whether external or incorporated in the processor, shall ensure adequate
supplies for the correct operation of the equipment, for operation within an ambient
temperature range of at least 5 °C to 40 °C and, if mains operated, for mains voltage
variations of 10 % around nominal.
Battery operated power supplies shall be equipped with an indicator to show that the bat-
tery voltage is sufficient for the correct operation of the equipment.
10 Sound intensity probe calibrators: requirements
Calibrators intended for use with specific types of probes shall have markings to that
effect or full information shall be given in the instruction manual.
10.1 Sound pressure calibrators
Sound pressure calibrators shall meet the requirements of IEC 942 for class 0, 1 or 2
calibrators.
10.2 Residual intensity testing devices
Residual intensity testing devices shall operate over the whole or part of the frequency
range from 45 Hz to 7,1 kHz, providing pink or white noise.
1043 ©IEC:1993 - 35 -
At least in the frequency range of 45 Hz to 1 000 Hz, the testing device shall apply sound
pressure to the two microphones at the same level within ±0,1 dB and the phase angle
difference, in degrees, between the two acoustic signals shall be less than
-6
f x 10
54,2° x
1 Hz
where
f is the frequency, in hertz.
10.3 Sound intensity calibrators
Calibrators for direct sound intensity calibration shall deliver to the probe microphones the
simulated sound intensities specified by the manufacturer within a tolerance of ±0,5 dB at
a specified temperature, atmospheric pressure and nominal microphone separation.
Dependence on atmospheric pressure, temperature and humidity shall be stated by the
manufacturer.
11 Sound intensity processors: performance verification
11.1
Octave and one-third octave filters
The filter attenuation characteristics of both channels of the processor shall be tested for
compliance with the requirements of IEC 1260 (under consideration). The processor
should be tested in pressure mode with sinusoidal input signals. One-third octave filter
bands between 50 Hz and 6,3 kHz shall be tested. If only octave band filtering is imple-
mented, octave bands from 63 Hz to 4 kHz shall be tested. Tolerances apply around
reference attenuation or input (if, for example, the processor has a direct voltage reading
facility, 1 V input becomes the reference value).
Linearity shall be tested in each of these bands by applying sinusoidal input signals to the
processor in pressure mode. Set the processor for microphone sensitivities of 12 mV/Pa,
or the nearest available setting. Set the processor to indicate 100 dB full-scale indication,
or the highest full-scale range available if this is lower than 100 dB. Adjust the input to the
processor to give an output 22 dB lower than that which causes an overload indication in
the processor. Record the sound pressure level indicated by the processor at this refer-
ence point. Increase the input to the processor in four steps of 5 dB and record the sound
pressure level indicated by the processor after each step. For class 1 instruments reduce
the input to the processor in four steps of 5 dB from the reference point and record the
sound pressure level indicated by the processor after each step. For class 2 instruments
reduce the input to the processor in two steps of 5 dB from the reference point and record
the sound pressure level indicated by the processor after each step. The indication of the
instrument shall be correct within ±0,2 dB at each step.
1043 ©IEC:1993 - 37 -
A-weighting, if provided, shall be verified at the band centre frequencies for compliance
with 6.3 above.
11.2
Sound intensity indication
Test the processor electrically, with sinusoidal signals fed into the two channels simul-
taneously from a generator system which provides an accurately known phase difference
between the two signals. The test signal levels shall be the same (±0,1 dB), and chosen to
represent sound pressure levels 20 dB below full-scale indication of a convenient range.
Use test frequencies of 63 Hz, 250 Hz, 1 kHz and 4 kHz. Set the instrument to read sound
pressure level in octave or one-third octave bands, average the signal and record this
reading. Set the processor to intensity mode, calculating intensity for a probe separation
of 10 mm to 100 mm, and, if possible, calculating for an atmospheric pressure of
101,3 kPa and a temperature of 20 °C. Set the phase angle a, in degrees, between the
input signals to be
dr x f x 360°
a =
cx 10 1'2
where
dr is the microphone separation, in metres;
f is the frequency, in hertz; and
c is the speed of sound at reference conditions, in metres per second (343,37).
The phase angle between the two inputs shall be accurately known to ±2 % when verifying
class 1 instruments and ±3,5 % when verifying class 2 instruments. Record the intensity
indicated by the processor. Interchange the two inputs to the processor and record the
new intensity indicated by the processor. The mean of the two recorded intensity levels
shall be L I = Lp — 12 , 15 dB within the tolerance in table 1 for "indicator accuracy".
With the same input signal, a change in the probe microphone separation setting shall
result in a change of sound intensity reading of 10 Ig (dri /dr2) dB where drt and dr2 are
the original and subsequent microphone separation settings. The change of reading shall
be within the tolerances for "microphone separation setting accuracy" in table 1.
NOTE — Electrical signals with accurately known phase differences can be generated by a single channel
generator and the RC networks described in annex D.
11.3
Time averaging
With the processor in pressure mode, apply a 6,3 kHz sinusoidal signal (or 4 kHz if the
processor only has one octave analysis) simultaneously to both inputs. Average the signal
for a time T, equal to the longest averaging time required by this Standard for the class of
processor (see table 1), and record the result L 1 . Then apply the signal for a time T/10
while still averaging for a time T and record the result L2. The two results shall be related
by L2 = L 1 - 10 dB within ±0,3 dB for class 1 processors and ±0,5 dB for class 2 and 2X
processors.
1043 ©IEC:1993 - 39 -
Apply the signal for a time T/10 and average for a time T/4, record the result
L3. L 1 and L3
shall be related by L3 = L 1 - 4 dB within the above tolerances.
11.4 Crest factor handling
With the processor in pressure mode, apply a steady 2 kHz sinusoidal signal, average for
-<
a time T, where 30 s <_ T 36 s, and record the result in decibels L 1 . Then apply a series
of 2 kHz tone bursts, of 4 ms duration, with a burst repetition rate of 20 Hz. Each burst
shall start and end at zero, include eight complete cycles, and have the same peak ampli-
tude as the steady signal. Average this signal for a time T and record the result L2 for the
2 kHz octave band.
L 1 and L2 shall be related by L2 = L 1 - 11 dB within ±0,3 dB for class 1 processors and
±0,5 dB for class 2 processors.
Repeat the test with tone burst durations of 8 ms (16 complete cycles) and a burst
repetition rate of 10 Hz where the same relationship exists.
If a 2 kHz octave band filter is not available in the processor, tests shall be made with
the 2 kHz one-third octave band filter. In which case L 1 and L2 shall be related by
L2 = L 1 - 11,3 dB within the above tolerances.
11.5
Pressure-residual intensity index and operating range
Set the processor to indicate sound pressure and sound intensity, calculating intensity for
a probe separation of 25 mm (or nearest available), and, if possible, calculating for an at-
mospheric pressure of 101,3 kPa and a temperature of 20 °C. Set the processor for
microphone sensitivities of 12 mV/Pa, or the nearest available setting.
Apply a pink noise electrical signal with a peak to rms ratio of at least 4, into both
channels of the processor, through a calibrated step attenuator. The signal may be band
limited from 20 Hz to 20 kHz. Set the processor to indicate 140 dB full-scale indication or
the highest full-scale range available if this is lower than 140 dB. Adjust the input to the
processor to give an output 2 dB lower than that which causes an overload indication in
the processor.
Determine the pressure-residual intensity index by averaging the signal for at least 60 s
and calculating it from the pressure and intensity indications on the processor.
Reduce the input signal by 10 dB, and without changing the processor range, determine
the pressure-residual intensity index.
Reduce the full-scale indication of the processor by 10 dB and without changing the input
signal, determine the pressure-residual intensity index.
1043 © I EC:1993 - 41 -
Repeat the procedure of reducing the input signal, determining the pressure-residual inten-
sity index reducing the full-scale indication, determining the pressure-residual intensity
index etc. until a pressure-residual intensity index determination, in any band, fails to meet
the requirements of table 2.
The difference between the arithmetic mean of the set of band sound pressure levels,
measured with the highest input signal, and the arithmetic mean of the set of band sound
pressure levels measured with the lowest input signal where the requirements for pressure-
residual intensity were met, is the operating range of the processor.
12 Sound intensity probes: performance verification
For the purpose of these tests, "the probe" means that pa
rt of the probe assembly which
mechanically locates the microphones, together with any components essential to the
probe operation.
In the following tests, if no class 1 processor suitable for use with a particular class 2
probe exists, then a class 2 processor may be used.
12.1
Frequency response
Connect the probe to a class 1 processor appropriate to the probe and adjust the sen-
sitivity of the complete system using the calibration device specified by the probe manu-
facturer, in accordance with the manufacturer's instructions.
Align the probe in a sound field so that plane progressive waves are incident on it from the
reference direction. Determine the free-field sound intensity response of the probe and the
responses of the individual microphones, by comparison with a microphone of known free-
field response.
Determine the responses, for each configuration of the probe, at one-third octave intervals
in the frequency range 500 Hz to 6,3 kHz excluding any frequencies outside the range of
operation claimed by the manufacturer. The responses shall comply with the requirements
of table 3.
As the sound intensity response of the probe is not measured at 250 Hz, the formula in 7.3
above may be used to calculate the nominal response relative to a frequency which is in
the measurement range. The tolerances of table 3 will still apply.
NOTES
1 Testing may be carried out using continuous sinusoidal signals, or tone bursts gated electronically into
the processor. The use of continuous sinusoidal signals places extreme demands on the quality of the free-
field chamber in which testing is carried out, and may not be practicable. Alternatively, testing may be
carried out using pink noise, in which case the demands on the quality of the fre
...
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