CEN/TS 1793-5:2003

SLOVENSKI STANDARD
01-junij-2004
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Road traffic noise reducing devices - Test method for determining the acoustic
performance - Part 5: Intrinsic characteristics - In situ values of sound reflection and
airborne sound insulation
Lärmschutzeinrichtungen - Prüfverfahren für die Lärmmessung
Dispositifs de réduction du bruit du trafic routier - Méthode d'essai pour la détermination
de la performance acoustique - Partie 5: Caractéristiques intrinseques - Valeurs in situ
de réflexion acoustique et d'isolation aux bruits aériens
Ta slovenski standard je istoveten z: CEN/TS 1793-5:2003
ICS:
17.140.30 Emisija hrupa transportnih Noise emitted by means of
sredstev transport
93.080.30 Cestna oprema in pomožne Road equipment and
naprave installations
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL SPECIFICATION
CEN/TS 1793-5
SPÉCIFICATION TECHNIQUE
TECHNISCHE SPEZIFIKATION
March 2003
ICS 17.140.30, 93.080.30
English version
Road traffic noise reducing devices — Test method for
determining the acoustic performance — Part 5: Intrinsic
characteristics - In situ values of sound reflection and airborne
sound insulation
Lärmschutzeinrichtungen an Straßen - Prüfverfahren zur
Bestimmung der akustichen Eigenschaften - Teil 5:
Produktspezifische Merkmale - In-situ-Werte der
Schallreflexion und der Luftschalldämmung
This Technical Specification (CEN/TS) was approved by CEN on 27 October 2002 for provisional application.
The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to submit their
comments, particularly on the question whether the CEN/TS can be converted into a European Standard.
CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS available. It
is permissible to keep conflicting national standards in force (in parallel to the CEN/TS) until the final decision about the possible
conversion of the CEN/TS into an EN is reached.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2003 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TS 1793-5:2003 E
worldwide for CEN national Members.

Contents
Foreword. 4
Introduction . 5
1 Scope. 6
2 Normative references . 7
3 Terms and definitions. 7
4 Reflection index measurements. 10
4.1 General principle. 10
4.2 Measured quantity. 13
4.3 Measuring equipment . 15
4.3.1 Components of the measuring system. 15
4.3.2 Sound source . 16
4.3.3 Test signal. 16
4.4 Data processing . 17
4.4.1 Calibration. 17
4.4.2 Sample rate. 17
4.4.3 Background noise. 17
4.4.4 Signal subtraction technique. 17
4.4.5 Adrienne temporal window . 18
4.4.6 Placement of the Adrienne temporal window . 19
4.4.7 Low frequency limit and sample size. 20
4.5 Positioning of the measuring equipment . 21
4.5.1 Maximum sampled area. 21
4.5.2 Selection of the measurement positions. 22
4.5.2.1 Flat homogeneous samples . 22
4.5.2.2 Non flat or non homogeneous samples in one direction. 22
4.5.2.3 Non flat or non homogeneous samples in two directions . 25
4.5.3 Reflecting objects . 26
4.5.4 Safety considerations. 26
4.6 Sample surface and meteorological conditions . 26
4.6.1 Condition of the sample surface . 26
4.6.2 Wind. 26
4.6.3 Air temperature. 26
4.7 Single-number rating of sound reflection DL . 27
RI
4.8 Measuring procedure. 27
4.9 Test report. 28
5 Sound insulation index measurements . 29
5.1 General principle. 29
5.2 Measured quantity. 29
5.3 Measuring equipment . 32
5.3.1 Components of the measuring system. 32
5.3.2 Sound source . 33
5.3.3 Test signal. 33
5.4 Data processing . 33
5.4.1 Calibration. 33
5.4.2 Sample rate. 33
5.4.3 Background noise. 33
5.4.4 Scanning technique . 34
5.4.5 Adrienne temporal window . 34
5.4.6 Placement of the temporal window. 34
5.4.7 Low frequency limit and sample size. 35
5.5 Positioning of the measuring equipment . 36
5.5.1 Selection of the measurement positions.36
5.5.2 Post measurements.36
5.5.3 Additional measurements .37
5.5.4 Reflecting objects .37
5.5.5 Safety considerations.37
5.6 Sample surface and meteorological conditions .37
5.6.1 Condition of the sample surface .37
5.6.2 Wind .37
5.6.3 Air temperature .37
5.7 Single-number rating of airborne sound insulation DL .37
SI
5.7.1 Elements .38
5.7.2 Posts.38
5.8 Measuring procedure.38
5.9 Test report .39
Annex A (informative)  Definition and usage of the MLS signal .41
A.1 The MLS test signal .41
A.2 Recovering of the overall impulse response .41
A.3 Sample rate and MLS time length .41
A.4 Improvement of the signal-to-noise ratio .42
Bibliography .43
Foreword
This document (CEN/TS 1793-5:2003) has been prepared by Technical Committee CEN/TC 284 “Road
equipment”, the secretariat of which is held by AFNOR.
This Technical Specification has been prepared, under the direction of Technical Committee CEN/TC 226 “Road
equipment”, by Working Group 6 “Anti noise devices”.
It should be read in conjunction with :
EN 1793-1, Road traffic noise reducing devices - Test method for determining the acoustic performance –
Part 1 : Intrinsic characteristics of sound absorption
EN 1793-2, Road traffic noise reducing devices - Test method for determining the acoustic performance –
Part 2 : Intrinsic characteristics of airborne sound insulation
EN 1793-3, Road traffic noise reducing devices - Test method for determining the acoustic performance –
Part 3 : Normalized traffic noise spectrum
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to anounce this Technical Specification: Austria, Belgium, Czech Republic, Denmark, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal,
Slovakia, Spain, Sweden, Switzerland and the United Kingdom.
Introduction
This document describes a test method for determining the intrinsic characteristics of sound reflection and airborne
sound insulation of traffic noise reducing devices. It can be applied in situ, i.e. where the noise reducing devices
are installed. The method can be applied without damaging the surface.
The method can be used to qualify products to be installed along roads as well as to verify the compliance of
installed noise reducing device to design specifications. Regular application of the method can be used to verify the
long term performance of noise reducing devices.
The method requires the average of results of measurements taken in different points in front of the device under
test and/or for specific angles of incidences. The method is able to investigate flat and non flat products.
The method uses the same principles and equipment for measuring sound reflection and airborne sound insulation.
The measurements results of this method for sound reflection are not directly comparable with the results of the
laboratory method (EN 1793-1), mainly because the present method uses a directional sound field, while the
laboratory method assumes a diffuse sound field. Moreover, this method introduces a specific quantity, called
reflection index, to define the sound reflection in front of a noise reducing device, while the laboratory method gives
a sound absorption coefficient. Laboratory values of the sound absorption coefficient can be converted to
conventional values of a reflection coefficient taking the complement to one. In this case, research studies suggest
that a quite good correlation exists between laboratory data, measured according to EN 1793-1 and field data,
measured according to the method described in the present document.
The measurements results of this method for airborne sound insulation are comparable but not identical with the
results of the laboratory method (EN 1793-2), mainly because the present method uses a directional sound field,
while the laboratory method assumes a diffuse sound field. This method introduces a specific quantity, called
sound insulation index, to define the airborne sound insulation of a noise reducing device. This quantity should not
be confused with the sound reduction index used in building acoustics, sometimes also called transmission loss.
Research studies suggest that a very good correlation exists between laboratory data, measured according to
EN 1793-2, and field data, measured according to the method described in the present document.
NOTE – This method may be used to qualify noise reducing devices for other applications, e.g. to be installed along railways or
nearby industrial sites. In this case the single-number ratings should be calculated using an appropriate spectrum.
1 Scope
The present document describes a test method for measuring two quantities representative of the intrinsic
characteristics of traffic noise reducing devices : the reflection index for sound reflection and the sound insulation
index for airborne sound insulation.
The test method is intended for the following applications :
 determination of the intrinsic characteristics of sound reflection and airborne sound insulation of noise reducing
devices to be installed along roads, to be measured either in situ or in laboratory conditions ;
 determination of the in situ intrinsic characteristics of sound reflection and airborne sound insulation of noise
reducing devices in actual use ;
 comparison of design specifications with actual performance data after the completion of the construction
work ;
 verification of the long term performance of noise reducing devices (with a repeated application of the method).
The test method can be applied both in situ and on barriers purposely built to be tested using the method described
here. In the second case the sample shall be built as follows (see Figure 1) :
 a part, composed of acoustic elements, that extends 4 m and is 4 m high ;
 a post 4 m high (if applicable for the specific noise reducing device under test) ;
 a part, composed of acoustic elements, that extends at least 2 m and is 4 m high ;
NOTE For qualifying the reflection index only, it is only necessary to have acoustic elements that extend 4 m or more.
NOTE For qualifying the sound insulation index of posts only, it is only necessary to have acoustic elements that extend
2 m or more on either side of the post (see Figure 1).
Results are expressed as a function of frequency, in one-third octave bands between 100 Hz and 5 kHz. If it is not
possible to get valid measurements results over the whole frequency range indicated, the results shall be given in
the restricted frequency range and the reasons of the restriction(s) shall be clearly reported.
4 m 2 m 2 m 2 m
4 m
4 m
Figure 1 (a) Figure 1 (b)
Figure 1 — Sketch of the sample required for measuremnts in laboratoy conditions - (a) : Reflection index
and sound insulation index measurements (elements and posts) - (b) : sound insulation index
measurements in front of a post only
2 Normative references
This Technical Specification incorporates by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate place in the text and the publications are listed hereafter. For
dated references, subsequent amendments to or revisions of any of these publications apply to this Technical
Specification only when incorporated in it by amendment or revision. For undated references, the latest edition of
the publication applies (including amendments).
EN 1793-3, Road traffic noise reducing devices - Test method for determining the acoustic performance –
Part 3: Normalized traffic noise spectrum.
EN 60651, Sound level meters.
3 Terms and definitions
For the purposes of this Technical Specification the following terms and definitions apply.
3.1
structural elements
those elements whose primary function is to support or hold in place acoustic elements
3.2
acoustical elements
those elements whose primary function is to provide the acoustic performance of the device
3.3
roadside exposure
use of the product as a noise reducing device installed alongside roads
3.4
reflection index
result of a sound reflection test described by formula (1)
3.5
reference height
height h equal to half the height h of the noise reducing device under test : h = h /2 (see Figure 2)
S B S B
3.6
reference axis of rotation-front panel distance for the loudspeaker
distance between the centre of rotation of the loudspeaker cabinet and its front panel ; it is equal to : d = 0,15 m
RS
(see Figure 2)
NOTE The actual dimensions of the loudspeaker used for the background research on which this Technical Specification is
based are : 0,40 x 0,285 x 0,285 m (length x width x height)
3.7
reference loudspeaker-microphone distance
distance between the front panel of the loudspeaker and the microphone ; it is equal to : d = 1,25 m (see
SM
Figure 2)
3.8
reference circle for reflection index measurements
circle of radius equal to 1,65 m (= d + d + d ) with centre at the reference height, drawn so that is just touches
RS SM M
the noise reducing device under test. The centre of the circle lies on the axis of rotation of the sound source (see
Figure 2)
3.9
reference microphone position for reflection index measurements
point where the microphone is located when the loudspeaker-microphone assembly is horizontal normal to the noise reducing
device under test at the reference height (see Figure 2) and as far as possible from the edges of the sample ; additional
reference positions can be defined for non flat or non homogeneous samples (see 4.5.2.2 and 4.5.2.3)
3.10
rotation of the loudspeaker-microphone assembly
set of nine measurement positions, including the reference position, reached rotating the loudspeaker-microphone
assembly, around the axis of rotation R (see Figure 2), on the same plane in steps of 10° (Figure 4.a, 5, 6)
3.11
free-field measurement for reflection index measurements
measurement taken moving and/or rotating the loudspeaker-microphone assembly in order to avoid to face any
nearby object, including the ground (Figure 4.b)
3.12
maximum sampled area
surface area, projected on a front view of the noise reducing device under test for reflection index measurements,
which must remain free of reflecting objects causing parasitic reflections
1 Reference circle
Figure 2 — (not to scale) Sketch of the loudspeaker-microphone assembly in front of the noise reducing
device under test for reflection index measurements - R : axis of rotation. S : loudspeaker front panel.
M : microphone
3.13
sound insulation index
result of airborne sound insulation test described by formula (7)
3.14
measurement grid for sound insulation index measurements
vertical measurement grid constituted by nine equally spaced points. This measurement grid shall be squared, with
a side length 2 s of 0,80 m. Its centre shall be located at the reference height. The grid shall be placed facing the
side of the noise reducing device under test opposite to the side to be exposed to noise when the device is in
place, so that its horizontal distance to the closest point of the device is 0,25 m (see Figure 3). The grid shall be
placed at a distance as large as possible from the edges of the noise reducing device under test
3.15
source reference position for sound insulation index measurements
position facing the side to be exposed to noise when the device is in place, located at the reference height and
placed so that its horizontal distance to the closest point of the device is d = 1 m (see Figure 3)
s
s
1 2 3
4 5 6
s
7 8 9
h
S
Figure 3 (a) Figure 3 (b)
d
S
s
d
h
B M
h
S
Figure 3 (c)
Figure 3 — (not to scale) (a) : Measurement grid for sound insulation index measurements (front view,
receiver side) - (b) : Numbering of the measurement points - (c) : placement of the measurement grid
(side view)
3.16
free-field measurement for sound insulation index measurements
measurement taken displacing the loudspeaker and the microphone in the free field in order to avoid to face any
nearby object, including the ground (Figure 13.b)
3.17
adrienne temporal window
composite temporal window described in 4.4.5
3.18
background noise
noise coming from sources other than the source emitting the test signal
3.19
signal-to-noise ratio, S/N
difference in decibels between the level of the test signal and the level of the background noise at the moment of
detection of the useful event (within the Adrienne temporal window)
3.20
impulse response
time signal at the output of a system when a Dirac function is applied to the input. The Dirac function, also called d
function, is the mathematical idealisation of a signal infinitely short in time that carries a unit amount of energy
4 Reflection index measurements
4.1 General principle
The sound source emits a transient sound wave that travels past the microphone position to the device under test
and is then reflected on it (Figures 4.a, 5, 6). The microphone placed between the sound source and the device
under test receives both the direct sound pressure wave travelling from the sound source to the device under test
and the sound pressure wave reflected (including scattering) by the device under test. The power spectra of the
direct and the reflected components, corrected to take into account the path length difference of the two
components, gives the basis for calculating the reflection index.
The measurement must take place in an essentially free field in the direct surroundings of the device, i.e. a field
free from reflections coming from surfaces other than the surface of the device under test. For this reason, the
acquisition of an impulse response having peaks as sharp as possible is recommended : in this way, the reflections
coming from other surfaces than the tested device can be identified from their delay time and rejected.
d
S
50°
R S
M
h
B
90°
d d
SM M
h
S
130°
Figure 4 (a)
S M
d
SM
h
S
Figure 4 (b)
Figure 4 — Sketch of the set-up for the reflection index measurement (example for rotation in vertical
direction) - R : axis of rotation - S : loudspeaker front panel - M : microphone - (a) : Reflected sound
measurements, from 50° to 130° in step of 10° on the same rotation plane, in front of a non flat noise
reducing device - (b) : Reference “free-field” sound measurement
d
S
50°
R S
M
h
B
90°
d d
SM M
h
S
130°
Figure 6 (a)
d
S
50°
R
S M
h
B
90°
d d
SM M
h
S
130°
Figure 6 (b)
Figure 6 — Sketch of the set-up for the reflection index measurement (example for rotation in vertical
direction) - R : axis of rotation - S : loudspeaker front panel - M : microphone - (a) : Reflected sound
measurements, from 50° to 130° in step of 10° on the same rotation plane, in front of a concave noise
reducing device - (b) : Reflected sound measurements, from 50° to 130° in step of 10° on the same rotation
plane, in front of a convex noise reducing device
4.2 Measured quantity
The expression used to compute the reflection index RI as a function of frequency, in one-third octave bands, is :
F[]t ⋅ h ()t ⋅ w ()t df
r,k r
∫
n
j
Df
j
RI = (1)
j ∑
n
j
F[]t ⋅ h ()t ⋅ w ()t df
k=1
i i
∫
Df
j
where
h (t) is the incident reference component of the free-field impulse response ;
i
h (t) is the reflected component of the impulse response at the k-th angle ;
rk
w (t) is the incident reference free-field component time window (Adrienne temporal window) ;
i
w (t) is the reflected component time window (Adrienne temporal window) ;
r
F is the symbol of the Fourier transform ;
j is the index of the one-third octave frequency bands (between 100 Hz and 5 kHz) ;
Df is the width of the j-th one-third octave frequency band ;
j
n is the number of angles on which to average (n £ 9 per rotation ; see 4.5.2 and Table 1) ;
j
t is a time whose origin is at the beginning of the impulse response acquired by the measurement
chain.
NOTE The reflections from different portions of the surface under test arrive at the microphone position at different times,
depending on the travel path from the loudspeaker to the position of each test surface portion and back. The longer the travel
path from the loudspeaker to a specific test surface portion and back, the greater the time delay. Thus, the amplitude of the
reflected sound waves from different test surface portions, as detected at the microphone position, is attenuated in a manner
inversely proportional to the travel time. In order to compensate for this effect, t is included as a factor in both numerator and
denominator in formula (1).
NOTE Part of these devices can be integrated into a frequency analyser or a personal computer equipped with specific
add-on board(s).
The essential components of the measuring system are shown in figure 7.
The complete measuring system shall meet the requirements of at least a type 1 instrument in accordance with
EN 60651, except for the microphone which shall meet the requirements for type 2 and have a diameter of ½”
maximum.
NOTE The measurement procedure here described is based on ratios of the power spectra of signals extracted from
impulse responses sampled with the same equipment in the same place under the same conditions within a short time. Also, a
high accuracy in measuring sound levels is not of interest here. Strict requirements on the absolute accuracy of the
measurement chain are, therefore, not needed. Anyway, the requirement for a type 1 instrument is maintained for compatibility
with other European Standards. The microphone should be sufficiently small and lightweight in order to be fixed in front of the
loudspeaker without moving : the signal subtraction technique (see 4.4.4) requires the loudspeaker and microphone relative
position be kept strictly constant. It is difficult to find on the market type1 microphones meeting this requirement. For this reason,
the microphone is allowed to meet the requirements for type 2.
4.3.2 Sound source
The electro-acoustic sound source shall meet the following characteristics :
 have a single loudspeaker driver ;
 be constructed without any port, e.g. to enhance low frequency response ;
 be constructed without any electrically active or passive components (such as crossovers) which can affect the
frequency response of the whole system ;
 have a smooth magnitude of the frequency response without sharp irregularities throughout the measurement
frequency range, resulting in an impulse response under free-field conditions with a length not greater than
3 ms.
NOTE As the reflection index is calculated from the ratio of energetic quantities extracted from impulse responses taken
using the same loudspeaker-microphone assembly within a short time period, the characteristics of the loudspeaker frequency
response are not critical, provided a good quality loudspeaker meeting the above prescriptions is used.
4.3.3 Test signal
The electro-acoustic source shall receive an input electrical signal consisting of an MLS signal (see Annex A). The
input signal has to be set in order to avoid any non-linearity of the loudspeaker.
The S/N ratio is improved by repeating the same test signal and synchronously averaging the microphone
response (see Annex A). At least 16 averages must be kept (see 4.8.h).
NOTE This Technical Specification recommends the use of a MLS signal as test signal. Anyway, a different test signal may
be used, provided that the results are exactly the same. This means that it must be clearly demonstrated that :
 the generation of the test signal is deterministic and exactly repeatable ;
 impulse responses are accurately sampled (without distorsions) on the whole frequency range of interest (one-third octave
bands between 100 Hz and 5 kHz) ;
 the test method maintains a good background noise immunity, i.e. the effective S/N ratio can be made higher than 10 dB
on the whole frequency range of interest within a short measurement time (no more than 5 minutes per impulse response) ;
 the sample rate can be chosen high enough to allow an accurate correction of possible time shifts in the impulse
responses between the measurement in front of the sample and the free-field measurement due to temperature changes
(see 4.4.2) ;
 the test signal is easy-to-use, i.e. it can be conveniently generated and fed to the sound source using only equiment which
is available on the market.
4.4 Data processing
4.4.1 Calibration
The measurement procedure here described is based on ratios of the power spectra of signals extracted from
impulse responses sampled with the same equipment in the same place under the same conditions. An absolute
calibration of the measurement chain with regard to the sound pressure level is therefore not needed. It is anyway
recommended to check the correct functioning of the measurement chain from the beginning to the end of
measurements.
4.4.2 Sample rate
The frequency at which the microphone response is sampled depends on the specified upper frequency limit of the
measurement and on the anti-aliasing filter type and characteristics.
The sample rate f shall have a value greater than 43 kHz.
s
NOTE Although the signal is already unambiguously defined when the Nyquist criterion is met, higher sample rates
facilitate a clear reproduction of the signal. This document prescribes the use of the signal subtraction technique (see 4.4.4),
which implies knowledge of the exact wave form. Therefore, with the prescribed sample rates errors can be detected and
corrected more easily, such as time shifts in the impulse responses between the measurement in front of the sample and the
free-field measurement due to temperature changes.
The sample rate must be equal to the clock rate of the signal generator.
The cut-off frequency of the anti-aliasing filter, f , shall have a value :
co
f£kf (2)
co s
where k = 1/3 for the Chebyshev filter and k = 1/4 for the Butterworth and Bessel filters.
For each measurement, the sample rate, the type and the characteristics of the anti-aliasing filter shall be clearly
stated in each test report.
4.4.3 Background noise
The effective signal-to-noise ratio S/N, taking into account sample averaging, must be greater than 10 dB over the
frequency range of measurements.
NOTE Coherent detection techniques, such as the MLS cross-correlation, provide high S/N ratios (see Annex A).
4.4.4 Signal subtraction technique
After positioning the loudspeaker-microphone assembly as described in 3.9, the overall impulse response has to be
measured.
It consists of a direct component, a component reflected from the surface under test and other parasitic reflections
(Figure 8.a). The direct component and the reflected component from the device under test must be separated.
This Technical Specification requires this separation be done using the signal subtraction technique : the reflected
component is extracted from the overall impulse response after having removed the direct component by
subtraction of an identical signal (Figures 8.c and 8.d). This means that the direct sound component must be
exactly known in shape, amplitude and time delay. This can be obtained by performing a free-field measurement
using the same geometrical configuration of the loudspeaker and the microphone. In particular, their relative
position must be kept strictly constant. This requirement can be obtained by using a fixed and stable connection
between the source and the microphone. The direct component is extracted from the free-field measurement
(Figure 8.b).
This technique allows broadening of the time window, leading to a lower frequency limit of the working frequency
range, without having very long distances between loudspeaker, microphone and device under test.
The principle of the signal subtraction technique is schematically illustrated in figure 8.
w w
i i’
r
u
time   time
Figure 8 (a) Figure 8 (b)
w w
i
r r
u u
time  time
i’
Figure 8 (c) Figure 8 (d)
Figure 8 — Principle of the signal subtraction technique - (a) : Overall impulse response including : direct
incident component (i), reflected component (r), unwanted parasitic components (u) - (b) : Free-field direct
component (i’) - (c) : Direct component cancellation from the overall impulse response using the free-field
direct component (i’) - (d) : Result
The measurement must take place in a sound field free from reflections coming from objects other than the device
under test. However, the use of a time window cancels out reflections arriving after a certain time delay, and thus
originating from locations further away than a certain distance (see 4.5.3).
4.4.5 Adrienne temporal window
For the purpose of this Technical Specification, windowing operations in the time domain shall be performed using
a temporal window, called Adrienne temporal window, with the following specifications (see Figure 9) :
 a leading edge having a left-half Blackman-Harris shape and a total length of 0,5 ms (“pre-window”) ;
 a flat portion having a total length of 5,18 ms (“main body”) ;
 a trailing edge having a right-half Blackman-Harris shape and a total length of 2,22 ms.
The total length of the Adrienne temporal window is T = 7,9 ms.
W ,ADR
NOTE A four-term full Blackman-Harris window of length T is :
W,BH
     p2 tp4 tp6 t
     
()
w t = a-a cos + a cos-a cos (3)
0 1 2 3
     
T T T
W ,BH W ,BH W ,BHŁłŁłŁł
where
a = 0,35875 ;
= 0,48829 ;
a
a = 0,14128 ;
a = 0,01168 ;
££0.t T
W ,BH
NOTE If the window length T has to be varied (this occurs only in exceptional cases) the lengths of the flat portion
W ,ADR
and the right-half Blackman-Harris portion shall have a ratio of 7/3. As an example, when testing very large samples the window
length can be enlarged in order to achieve a better low frequency limit.
The point where the flat portion of the Adrienne temporal window begins is called the marker point (MP).
1.2
MP
1.0
0.8
0.6
0.4
0.2
0.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0
t [ms]
Figure 9 — The Adrienne temporal window, with the marker point MP
4.4.6 Placement of the Adrienne temporal window
For the “free-field” direct component, the Adrienne temporal window shall be placed as follows :
 the first peak of the impulse response, corresponding to the direct component, is detected ;
 a time instant preceding the direct component peak of 0,2 ms is located ;
 the direct component Adrienne temporal window is placed so as its marker point corresponds to this time
instant.
w (t )
In other words, the direct component Adrienne temporal window is placed so as its flat portion begins 0,2 ms
before the direct component peak.
For the reflected component, the Adrienne temporal window shall be placed as follows :
 the time instant labelled by the direct component Adrienne temporal window marker point is located ;
 the time delay t= 2d / c is added to this time instant ; the resulting time instant is assumed as the position of
M
the reflected component Adrienne temporal window marker point ;
 the reflected component Adrienne temporal window is placed so as its marker point corresponds to this new
time instant.
In other words, the reflected component Adrienne temporal window is placed so as its flat portion begins 0,2 ms
before the first peak of the reflected component.
In computations involving the sound speed c, its temperature dependent value shall be assumed.
4.4.7 Low frequency limit and sample size
The method described in the present document can be used for different sample sizes.
The low frequency limit f of reflection index measurements depends on the shape and width of the Adrienne
min
temporal window. The width in turn depends on the smallest dimension (height or length) of the noise reducing
device under test and on the rotation angle of the loudspeaker-microphone assembly (see 4.5.2 and figure 2, 4.a,
5, 6). In fact, the following unwanted components must be kept out of the Adrienne temporal window for the
reflected components :
 the sound components diffracted by the edges of the noise reducing device under test ;
 the sound components reflected by the ground on the sound source side of the noise reducing device under
test.
For noise reducing devices having a height smaller than the length, the most critical component is that reflected by
the ground and therefore the critical dimension is the height.
For noise reducing devices having a height smaller than the length, the low frequency limit f for normal incidence
min
measurements as a function of the height of the noise reducing device under test is given in figure 10.
For low barrier heights and/or specific shapes it may be more appropriate to carry out the rotation in the horizontal
plane rather than in the vertical plane.
For qualification tests, the sample shall have minimum dimensions of 4 m in height by 4 m in length (see also
Figure 1). These conditions give a low frequency limit for the reflection index of about 173 Hz, i.e. measurements
are valid down to the 200 Hz one-third octave band. Measurement values below 173 Hz could be kept for
information.
2,000
1,900
1,800
1,700
1,600
1,500
1,400
1,300
1,200
1,100
1,000
h [m]
B
Figure 10 — Low frequency limit of reflection index measurements as a function of the height of the noise
reducing device under test for normal incidence measurements
4.5 Positioning of the measuring equipment
4.5.1 Maximum sampled area
The size of the maximum sampled area is defined by the shortest distances of the loudspeaker front panel and the
microphone to the reference circl
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