kSIST FprEN 1793-5:2025

SLOVENSKI STANDARD
oSIST prEN 1793-5:2023
01-november-2023
Nadomešča:
SIST EN 1793-5:2016/AC:2018
Protihrupne ovire za cestni promet - Preskusna metoda za ugotavljanje akustičnih
lastnosti - 5. del: Bistvene lastnosti - Terenske vrednosti odboja zvoka z uporabo
usmerjenega zvočnega polja
Road traffic noise reducing devices - Test method for determining the acoustic
performance - Part 5: Intrinsic characteristics - In situ values of sound reflection under
direct sound field conditions
Lärmschutzvorrichtungen an Straßen - Prüfverfahren zur Bestimmung der akustischen
Eigenschaften - Teil 5: Produktspezifische Merkmale - In-situ-Werte der Schallreflexion
in gerichteten Schallfeldern
Dispositifs de réduction du bruit du trafic routier - Méthode d'essai pour la détermination
de la performance acoustique - Partie 5: Caractéristiques intrinsèques - Valeurs in situ
de réflexion acoustique dans des conditions de champ acoustique direct
Ta slovenski standard je istoveten z: prEN 1793-5
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
oSIST prEN 1793-5:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN 1793-5:2023
oSIST prEN 1793-5:2023
CEN/TC 226
Date: 2022-09-19
prEN 1793-5:2022
CEN/TC 226
Secretariat: AFNOR
Road traffic noise reducing devices — Test method for determining the acoustic
performance — Part 5: Intrinsic characteristics — Sound absorption under direct sound
field conditions
Lärmschutzeinrichtungen an Straßen — Prüfverfahren zur Bestimmung der akustischen
Eigenschaften — Teil 5: Produktspezifische Merkmale — Schallabsorption in gerichteten
Schallfeldern
Dispositifs de réduction du bruit du trafic routier — Méthode d’essai pour la détermination
de la performance acoustique — Partie 5 : Caractéristiques intrinsèques — Absorption
acoustique dans des conditions de champ acoustique direct

ICS: 17.140.30, 93.080.30
Descriptors:
Document type: European Standard
Document subtype:
Document stage:  CEN Enquiry
Document language: E
C:\Users\massimo.garai\Documents\CEN TC226 WG6\EN 1793-5 2018-2022\EN 1793-5 2022-09-19\TG1
N619 prEN 1793-5 2022-09-19.docx STD Version 2.5a

oSIST prEN 1793-5:2023
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Contents Page
European foreword . 4
Introduction . 5
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 8
4 Symbols and abbreviations . 13
5 Sound reflection index measurements . 15
5.1 General principle . 15
5.2 Measured quantity . 15
5.3 Test arrangement . 19
5.3.1 Tests on purposely built full -size samples . 19
5.3.2 Installed road traffic noise reducing devices . 20
5.3.3 Inclined or curve road traffic noise reducing devices . 21
5.4 Measuring equipment . 25
5.4.1 Components of the measuring system . 25
5.4.2 Sound source . 25
5.4.3 Test signal . 26
5.5 Data processing . 27
5.5.1 Calibration . 27
5.5.2 Sample rate and filtering . 28
5.5.3 Background noise . 29
5.5.4 Signal subtraction technique . 30
5.5.5 Accurate alignment procedure . 31
5.5.6 Adrienne temporal window . 33
5.5.7 Placement of the Adrienne temporal window . 35
5.5.8 Maximum sampled area. 37
5.6 Positioning of the measuring equipment . 37
5.6.1 General . 37
5.6.2 Selection of the measurement positions. 38
5.6.3 Consideration of relevant and parasitic reflections . 46
5.6.4 Low-frequency limit . 49
5.6.5 Reflecting objects . 49
5.6.6 Safety considerations. 50
5.7 Sample surface and meteorological conditions . 50
5.7.1 Condition of the sample surface . 50
5.7.2 Wind . 50
5.7.3 Air temperature . 50
5.8 Single-number rating of sound absorption under a direct sound field DL . 50
RI
5.9 Measurement uncertainty . 51
5.10 Measuring procedure . 51
5.11 Test report . 52
Annex A (informative) Low-frequency limit and window width . 54
A.1 General . 54
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Annex B (informative) Measurement uncertainty . 59
B.1 General . 59
B.2 Measurement uncertainty based upon reproducibility data . 59
B.3 Standard deviation of repeatability and reproducibility of the sound reflection index . 59
Annex C (normative) Template of test report on sound reflection index of road traffic noise
reducing devices . 61
C.1 General . 61
C.2 Test setup (example) . 64
C.3 Test object and test situation (example) . 65
C.4 Test Results (example) . 67
C.4.1 Part 1 – Results in tabular form . 67
C.4.2 Part 2 – Results in graphic form. 68
C.5 Uncertainty (example) . 68
Annex D (informative) Indoor measurements for product qualification . 70
D.1 General . 70
D.2 Parasitic reflections . 70
D.3 Reverberation time of the room . 70
Bibliography . 71

oSIST prEN 1793-5:2023
prEN 1793-5:2023 (E)
European foreword
This document (prEN 1793-5:2023) has been prepared under the direction of Technical Committee
CEN/TC 226 “Road equipment”, by Working Group 6 “Noise reducing devices”, the secretariat of which is
held by AFNOR.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 1793-5:2016.
EN 1793-5:2023 includes the following significant technical changes with respect to EN 1793-5:2016:
— The definitions from 3.1 to 3.7 have been updated to be in accordance to the last version of EN 14388.
— The single number rating DL is now reported with one decimal digit.
RI
— Annex A on the low-frequency limit and the window width has been added.
— One value for the standard deviation of reproducibility and repeatability in each one-third octave
frequency band has been retained, in place of three values (min, max and median) as before (see
Table B.1).
— Annex C (template of the test report) is now normative.
— The example in C.5 on the declaration of the measurement uncertainty has been updated accordingly.
— Annex C of EN 1793-5:2016 has been deleted.
EN 1793-5:2023 is part of a series and should be read in conjunction with the the following:
EN 1793-1:2023, Road traffic noise reducing devices - Test method for determining the acoustic performance –
Part 1: Sound absorption under diffuse sound field conditions
EN 1793-2:2023, Road traffic noise reducing devices - Test method for determining the acoustic performance –
Part 2: Intrinsic characteristics - Airborne sound insulation under diffuse sound field conditions
EN 1793-3:2023, Road traffic noise reducing devices - Test method for determining the acoustic performance –
Part 3: Normalized noise spectrum
EN 1793-4:2023, Road traffic noise reducing devices - Test method for determining the acoustic performance –
Part 4: Intrinsic characteristics – Intrinsic sound diffraction
EN 1793-5:2023, Road traffic noise reducing devices - Test method for determining the acoustic performance –
Part 5: Intrinsic characteristics –Sound absorption under direct sound field conditions
EN 1793-6:2023, Road traffic noise reducing devices - Test method for determining the acoustic performance –
Part 6: Intrinsic characteristics – Airborne sound insulation under direct sound field conditions
oSIST prEN 1793-5:2023
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Introduction
This document describes a test method for determining the intrinsic characteristics of sound absorption of
road traffic noise reducing devices designed for roads in non-reverberant conditions (a measure of intrinsic
performance). The methodology assesses indirectly sound absorption by measuring sound reflection (the
complementary characteristics). It can be applied indoors or outdoors. Indoors, it can be applied in a
purposely built test facility (under direct sound field conditions). Outdoors, it can be applied in a purposely
built test facilities, e.g. near a laboratory or a factory, as well as in situ, i.e. where the road traffic 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 devices 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 measurement results of this method for sound absorption are not comparable with the results obtained
under diffuse sound field conditions (EN 1793-1:2023), mainly because the present method uses a
directional sound field, not a diffuse sound field. The test method described in the present document should
not be used to determine the intrinsic characteristics of sound absorption of road traffic noise reducing
devices to be installed in reverberant conditions, e.g. claddings inside tunnels or deep trenches.
For the purpose of this document reverberant conditions are defined based on the envelope, e, across the
road formed by the device under test, trench sides or buildings (the envelope does not include the road
surface) as shown by the dashed lines in Figure 1. Conditions are defined as being reverberant when the
percentage of open space in the envelope is less than or equal to 25 %, i.e. reverberant conditions occur
when w/e ≤ 0,25, where e = (w+h +h ).
1 2
This method introduces a specific quantity as a function of frequency, called reflection index, to define the
sound reflection in front of a road traffic noise reducing device and then calculate a single-number rating for
sound absorption from it, while the measurements under diffuse sound field conditions (according to
EN 1793-1:2023) gives a sound absorption coefficient as a function of frequency and then calculate a single-
number rating for sound absorption from it. Values of the sound absorption coefficient measured under
diffuse sound field conditions can be converted to conventional values of a reflection coefficient taking the
complement to one. In this case, research studies suggest that some correlation exists between diffuse sound
field data, measured according to EN 1793-1:2023 and direct sound field data, measured according to the
method described in this document [6] [9] [17] [18] [19].
NOTE This method can be used to qualify noise reducing devices for other applications, e.g. to be installed nearby
industrial sites. In this case, the single-number ratings can preferably be calculated using an appropriate spectrum.
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(a) Partial cover on both sides of the road; (b) Partial cover on one side of the road;
envelope, e = w+h +h . e = w+h . h = 0.
1 2 1 2
(c) Deep trench envelope, e = w+h +h . (d) Tall barriers or buildings; envelope,
1 2
e = w+h +h . In all cases r: road surface; w: width
1 2
of open space
Figure 1 — (not to scale) Sketch of the reverberant condition check in four cases
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1 Scope
This document describes a test method for measuring a quantity representative of the intrinsic
characteristics of sound reflection from road noise reducing devices, the sound reflection index, and then
calculate a single-number rating for sound absorption from it.
The test method is intended for the following applications:
— determination of the intrinsic characteristics of sound absorption of noise reducing devices to be
installed along roads, to be measured either on typical installations alongside roads or on a relevant
sample section;
— determination of the intrinsic characteristics of sound absorption of road traffic noise reducing devices
in actual use under direct sound field conditions;
— comparison of design specifications with actual performance data after the completion of the
construction work;
— verification of the long-term performance of road traffic noise reducing devices (with a repeated
application of the method).
The test method is not intended for the following applications:
— determination of the intrinsic characteristics of sound absorption of road traffic noise reducing devices
to be installed in reverberant conditions, e.g. inside tunnels or deep trenches.
Results for the sound reflection index are expressed as a function of frequency, in one-third octave bands,
where possible, between 100 Hz and 5 kHz. If it is not possible to get valid measurements results over the
whole frequency range indicated, the results should be given in a restricted frequency range and the reasons
of the restriction(s) should be clearly reported.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
EN 1793-3:2023, Road traffic noise reducing devices - Test method for determining the acoustic performance -
Part 3: Normalized traffic noise spectrum
EN 14389:2022, Road traffic noise reducing devices - Procedures for assessing long-term performance
EN 61672-1:2013, Electroacoustics - Sound level meters - Part 1: Specifications
ISO/IEC Guide 98-3:2008, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
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3 Terms and definitions
For the purposes of this document the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp/
— IEC Electropedia: available at https://www.electropedia.org/
3.1
road traffic noise reducing device
RTNRD
device designed to reduce the propagation of traffic noise away from the road environment
Note 1 to entry: An RTNRD can comprise acoustic elements (3.2) only or both structural (3.3) and acoustic elements.
Note 2 to entry: Applications of RTNRDs include noise barriers (3.5), claddings (3.6), covers (3.7) and added devices
(3.8).
3.2
acoustic element
element whose primary function is to provide the acoustic performance of the device
3.3
structural element
element whose primary function is to support or hold in place the parts of the RTNRD.
3.4
self-supporting acoustic element
acoustic element including its own structural element to support itself
3.5
noise barrier
road traffic noise reducing device which obstructs the direct transmission of airborne sound emanating
from road traffic
3.6
cladding
road traffic noise reducing device which is attached to a wall or other structure and reduces the amount of
sound reflected
3.7
cover
road traffic noise reducing device which either spans or overhangs the road
3.8
added device
additional component that influences the acoustic performance of the original road traffic noise reducing
device
Note 1 to entry: The added device is acting primarily on the diffracted energy.
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3.9
roadside exposure
use of the product as a noise reducing device installed alongside roads
3.10
sound reflection index
quantity representing the amount of sound not absorbed by the device under test
Note 1 to entry: Formula (1) specifies how to calculate the sound reflection index.
Note 2 to entry: The sound reflection index values in one-third octave bands are the result of a test according to the
present document.
3.11
measurement grid for sound reflection index measurements
measurement grid constituted of nine equally spaced microphones in a 3x3 squared configuration
Note 1 to entry: The orthogonal spacing between two subsequent microphones, either vertically or horizontally, is
s = 0,40 m.
Note 1 to entry: See Figure 3, 5 and 6.
Note 2 to entry: Microphones are numbered like in Figure 3.
3.12
reference height
height h equal to half the height, h , of the road traffic noise reducing device under test: h = h /2
S B S B
Note 1 to entry: When the height of the device under test is greater than 4 m and, for practical reasons, it is not
advisable to have a height of the source hS = hB/2, it is possible to have hS = 2 m, accepting the corresponding low
frequency limitation (see 5.6.2 and 5.6.4).
Note 2 to entry: See Figures 2 and 3.
3.13
source and microphone reference surface for sound reflection index measurements
ideal, smooth surface facing the sound source side of the road traffic noise reducing device under test and
just touching the most protruding and significant parts of it within the tested area
Note 1 to entry: The reference surface is as smooth as possible, and follows the inclination or curve of the device
under test within the tested area. For vertical and flat road traffic noise reducing devices, the reference surface is a
vertical plane. For inclined and flat road traffic noise reducing devices, the reference surface is a plane with the same
inclination. For curve and flat noise reducing devices, the reference surface is a curve surface with the same curvature.
Note 2 to entry: See Figures 2, 4, 7, 8, and 9.
3.14
source reference position
position facing the side to be exposed to noise when the road traffic noise reducing device is in place, located
at the reference height h and placed so that the horizontal distance of the source front panel to the
S
reference surface is d = 1,50 m
S
Note 1 to entry: See Figures 2 and 3.
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3.15
measurement grid reference position
position of the measurement grid during the test
Note 1 to entry: the conditions and distances for a correct measurement reference position are specified in 5.6.2.1.
Note 2 to entry: for flat noise reducing devices, see Figures 2, and 3. For non-flat noise reducing devices, see Figure 7.
For inclined or curved noise reducing devices, see Figures 8 and 9.
3.16
reference loudspeaker-measurement grid distance
distance between the front panel of the loudspeaker and the central microphone (microphone n. 5) of the
measurement grid
Note 1 to entry: The reference loudspeaker-measurement grid distance is equal to dSM = 1,25 m (see Figures 2 and
4).
3.17
free-field measurement for sound reflection index measurements
measurement taken with the loudspeaker and the measurement grid in an acoustic free field in order to
avoid reflections from any nearby object, including the ground, keeping the same geometry as when
measuring in front of the noise reducing device under test
Note 1 to entry: See Figure 4.
3.18
maximum sampled area
surface area, projected on a front view of the road traffic noise reducing device under test for reflection
index measurements, which must remain free of reflecting objects causing parasitic reflections
3.19
Adrienne temporal window
analysis window in the time domain to be used for the data processing
Note 1 to entry: Data processing according to the present document.
Note 1 to entry: The Adrienne temporal window is described in 5.5.6.
3.20
background noise
noise coming from sources other than the sound source emitting the test signal
3.21
signal-to-noise ratio
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)
3.22
impulse response
time signal at the output of a system when a Dirac function is applied to the input
Note 1 to entry: The Dirac function, also called δ function, is the mathematical idealisation of a signal infinitely short
in time that carries a unit amount of energy.
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Note 2 to entry: It is impossible in practice to create and radiate true Dirac delta functions. Short transient sounds
can offer close enough approximations but are not very repeatable. An alternative measurement technique, generally
more accurate, is to use a period of deterministic, flat-spectrum signal, like maximum-length sequence (MLS) or
exponential sine sweep (ESS), and transform the measured response back to an impulse response.

Key
1 Source and microphone reference 2 Reference height hS [m]
surface
3 Loudspeaker front panel 4 Distance between the loudspeaker front panel and the reference
surface, dS [m]
5 Distance between the loudspeaker 6 Distance between the measurement grid and the reference
front panel and the measurement surface, d [m]
M
grid, dSM [m]
7 Measurement grid 8 Road traffic noise reducing device height, hB [m]
Figure 2 — (not to scale) Sketch of the sound source and the measurement grid in front of the road
traffic noise reducing device
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Key
1 road traffic noise reducing device height hB [m] 2 Reference height hS [m]
3 Orthogonal spacing between two subsequent
microphones s [m]
Figure 3 — (not to scale) Measurement grid for sound reflection index measurements in front of the
device under test (sound source side); the yellow circles indicate the microphone positions, labelled
from M1 to M9
Key
1 Reference height hS [m] 2 Distance between the loudspeaker front panel and the
[m]
measurement grid dSM
3 Loudspeaker front panel 4 Measurement grid
Figure 4 — (not to scale) Sketch of the set-up for the reference “free-field” sound measurement for
the determination of the sound reflection index
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4 Symbols and abbreviations
For the purposes of this document, the following symbols and abbreviations apply.
Table 1 – Symbols and abbreviations
Symbol or Designation Unit
abbreviation
a major axis of the ellipsoid of revolution used to define the maximum sampled m
area at oblique incidence
a , a , a , a Coefficient for the expression of the four-term full Blackman-Harris window -
0 1 2 3
b Depth of the surface structure of the sample under test m
s
α Angle between the line connecting the centre of the front panel of the -
k
loudspeaker to microphone 5 and the line connecting the centre of the front
panel of the loudspeaker to microphone k
β Angle between the line connecting the centre of the front panel of the -
k
loudspeaker to microphone 5 and the line connecting the centre of the front
panel of the loudspeaker to the specular reflection path to microphone k
bm Width of a portion of material of the sample under test m
c Speed of sound in air m/s
C Correction factor for the geometrical divergence -
geo,k
C Correction factor for the sound source directivity -
dir,k
C Correction factor for changes in the sound source gain -
gain,k
d Horizontal distance from the source and microphone reference surface to the m
M
measurement grid; it is equal to d = 0,25 m
M
d Horizontal distance from the front panel of the loudspeaker to the source and m
S
microphone reference surface; it is equal to: d = 1,50 m
S
d Horizontal distance from the front panel of the loudspeaker to the measurement m
SM
grid; it is equal to: d = 1,25 m
SM
DL Single number rating of sound reflection dB
RI
δ Any input quantity to allow for uncertainty estimates -
i
Δf Frequency range encompassing the one-third octave frequency bands between Hz
g
500 Hz and 2 kHz
Δf Width of the j-the one-third octave frequency band Hz
j
Δt temporal step between the discrete points of the acquired data (linked to the ms
given sample rate by Δt = 1/f )
s
Δτ moving step of the free field impulse response in the adjustment procedure ms
included in the generalized signal subtraction technique (see 5.5.4)
Δt Time delay gap between the arrival of direct sound at microphone k (k ≠ 5) and s
k5
microphone 5
Δt Time delay gap between the arrival of direct and reflected sound at microphone k s
k
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Symbol or Designation Unit
abbreviation
Δd Path length difference between the arrival of direct sound at microphone k (k ≠ m
k5
5) and microphone 5
Δd Path length difference between the arrival of direct and reflected sound at m
k
microphone k
ε Tolerance on the path length difference at microphone k m
k
F Symbol of the Fourier transform -
f Frequency Hz
fmin Low frequency limit of sound reflection index measurements Hz
f Sample rate Hz
s
f cut-off frequency of the anti-aliasing filter Hz
co
h Noise reducing device height m
B
h Reference height m
S
h (t) Incident reference component of the free-field impulse response at the k-th -
i,k
measurement point
h (t) Reflected component of the impulse response at the k-th measurement point -
r,k
j Index of the j-th one-third octave frequency band (between 100 Hz and 5 kHz) -
hi,k,FF (t) Incident reference component of the impulse response taken in front of the -
sample under test at the k-th measurement point (before the signal subtraction)
h (t) Residual incident reference component of the impulse response taken in front of -
i,k,RES
the sample under test at the k-th measurement point (after the signal
subtraction)
k Index of the k-th measurement point (k = 1 … n ) -
j
k Coverage factor -
p
k Constant used for the anti-aliasing filter -
f
L Sample period length of a non-homogeneous noise reducing device m
p
n Number of measurement points on which to average -
j
n Number of reference positions of the measurement grid -
R
q Number of discrete data points of the acquired data used in the accurate -
alignment procedure to define the range where to apply the least square
procedure (see 5.5.5)
r Radius of the maximum sampled area at normal incidence m
R Reduction factor dB
sub
RI Sound reflection index in the j-th one-third octave frequency band -
j
RI Sound reflection index in the j-th one-third octave frequency band when the -
i,j
measurement grid is in the i-th reference position
s Orthogonal spacing between two subsequent microphones m
s Standard deviation of repeatability -
r
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Symbol or Designation Unit
abbreviation
s Standard deviation of reproducibility -
R
S/N Signal to noise ratio dB
t Time s
t Air temperature °C
C
T Length of the Blackman-Harris trailing edge of the Adrienne temporal window s
W,BH
T Total length of the Adrienne temporal window s
W,ADR
u Standard uncertainty -
U Expanded uncertainty -
w (t) Reference free-field component time window (Adrienne temporal window) at the -
i,k
k-th measurement point
w (t) Time window (Adrienne temporal window) for the reflected component at the k- -
r,k
th measurement point
5 Sound reflection index measurements
5.1 General principle
The sound source emits a transient sound wave that travels past the measurement grid (microphone)
position to the device under test and is then reflected on it (Figures 2 and 3). Each microphone, being 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 direct sound pressure wave can be better acquired with a separate
free field measurement (see Figure 4). The ratio of the power spectra of the direct and the reflected
components gives the basis for calculating the sound reflection index.
The measurement shall 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.
5.2 Measured quantity
The expression used to compute the reflection index RI as a function of frequency, in one-third octave bands,
is:


F h t ⋅w t df
( ) ( )
rk,,rk

∫
n
j
∆f

j
RI ⋅C⋅C∆⋅f C∆f (1)
( ) ( )
j geo,,k dir k j gain,k g
∑
n
j

k=1 Fh t ⋅w t df
( ) ( )
ik,,ik
∫ 

∆f
j

=
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where
h (t) is the incident reference component of the free-field impulse response at the k-th
i,k
measurement point;
h (t) is the reflected component of the impulse response taken in front of the sample under test
r,k
at the k-th measurement point;
w (t) is the time window (Adrienne temporal window) for the incident reference component of
i,k
the free-field impulse response at the k-th measurement point;
w (t) is the time window (Adrienne temporal window) for the reflected component at the k-th
r,k
measurement point;
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, where
possible);
∆f is the width of the j-th one-third octave frequency band;
j
k is the microphone number according to Figure 3.b (k = 1, ., 9);
n is the number of microphone positions on which to average (n ≥ 6; see 5.6);
j
j
C is the correction factor for geometrical divergence at the k-th measurement point;
geo,k
C (Δf ) is the correction factor for sound source directivity at the k-th measurement point.
dir,k j
C (Δf ) is the correction factor to account for a change in the amplification settings of the
gain,k g
loudspeaker and in the sensitivity settings of the individual microphones when changing
the measurement configuration from free field to in front of the sample under test or vice
versa, if any (see 5.5.1 and Formula (4));
is the frequency range encompassing the one-third octave frequency bands between
∆f
g
500 Hz and 2 kHz.
The correction factors for geometrical divergence, C , are given by:
geo,k
d
rk,
C = (2)
geo,k

d
ik,

where
d is the distance from the front panel of the loudspeaker to the k-th measurement point;
i,k
d is the distance from the front panel of the loudspeaker to the source and microphone
r,k
reference plane and back to the k-th measurement point following specular reflection;
k is the microphone number according to Figure 3 (k = 1, ., 9).
NOTE 1 For the microphone n. 5, d = d = 1,25 m
i,5 SM
The distances d , d and the correction factors C are given in Table 2 for a plane reference surface.
geo,k
i,k r,k
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Table 2 – Distances d , d and correction factors C for a plane reference surface
geo,k
i,k r,k
k d , m d , m C
i,k r,k geo,k
1 1,37 1,84 1,80
2 1,31 1,80 1,87
3 1,37 1,84 1,80
4 1,31 1,80 1,87
5 1,25 1,75 1,96
6 1,31 1,80 1,87
7 1,37 1,84 1,80
8 1,31 1,80 1,87
9 1,37 1,84 1,80
NOTE 2 The reflections from different portions of the surface of the device 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 positions, is attenuated in a manner inversely proportional to the travel time. For non-flat,
complex devices it is difficult to predict the exact travel path of each wave, considering also non specular scattering;
therefore, the geometrical divergence correction factors are calculated on the basis of specular reflection on an ideal
flat reflecting surface.
The correction factors for sound source directivity are given by:
 
F h t ,α ⋅w t df
( ) ( )
ik,,k ik
 
∫
∆f
j
C ∆f = (3)
( )
dir ,k j

F h t ,β ⋅w t df
( ) ( )
ik,,k ik
∫ 
∆f
j
where
α is the angle between the line connecting the centre of the front panel of the loudspeaker to
k
microphone 5 and the line connecting the centre of the front panel of the loudspeaker to
microphone k (see Figure 6.a);
β is the angle between the line connecting the centre of the front panel of the loudspeaker to
k
microphone 5 and the line connecting the centre of the front panel of the loudspeaker to the
specular reflection path to microphone k (see Figure 6.a);
h (t,α ) is the incident reference component of the free-field impulse response at the k-th
k
i,k
measurement point;
h (t,β ) is the incident reference component of the free-field impulse response at a point on the
k
i,k
specular reflection path for microphone k and at distance d from the centre of the front
i,k
panel of the loudspeaker;
w (t) is the time window (Adrienne temporal window) for the incident reference component of
i,k
the free-field impulse response at the k-th measurement point;
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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, where
possible);
∆f is the width of the j-th one-third octave frequency band;
j
k is the microphone number according to Figure 3 (k = 1, ., 9).
When measuring the sound source directivity correction factors, the numerator and denominator of the
ratio in Formula (3) shall be measured in two different points at the constant distance d (see Table 2) from
i,k
the centre of the front panel of the loudspeaker. The first point is placed at the microphone position and the
second point is placed on the specular reflection travel path of the sound emitted by the loudspeaker (see
Figure 5).
NOTE 3 For non-flat complex devices it is difficult to predict the exact travel path of each wave, considering also non
specular scattering; therefore, the correction factors for sound source directivity are calculated on the basis of specular
reflection on an ideal flat reflecting surface.
The sound source directivity correction factors shall be measured in the free field. The sound source
directivity correction factors shall be measured only once for each sound source, assuming that the source
directivity patterns don’t change. For the sake of accuracy, they may be measured again from time to time
(e.g. once a year).
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(a) microphone positions 4, 5, and 6 (white (b) front view of the nine microphone positions
circles), angles α and β for microphone 4 and (white circles) and the nine positions where the
4 4
the point, at a distance d from the loudspeaker specular reflection travel path of the sound
i,4
centre plate, where measurements to get the emitted by the loudspeaker intersect the plane of
correction factor C shall be done (grey circle) the measurement grid (black circles)
dir,4
Key
1 Loudspeaker 2 Sample under test
3 Horizontal distance from the source and 4 Microphone 4
microphone reference surface to the
measurement grid, dM [m]
5 Microphone 5 6 Microphone 6
7 Orthogonal spacing between two subsequent 8 Distance d from the loudspeaker centre plate to mic.
i,4
microphones, s [m] n. 4, where measurements to get the correction
factor Cdir,4 shall be done [m]
9 Angle α between the line connecting the centre of 10 Angle β between the line connecting the centre of the
4 4
the front panel of the loudspeaker to front panel of the loudspeaker to microphone n. 5
microphone n. 5 and the line connecting the and the line connecting the centre of the front
centre of the front panel of the loudspeaker to panel of the loudspeaker to the specular reflection
microphone n. 4 path to microphone n. 4
Figure 5 (not to scale) — Sketch showing microphone positions and angles for the calculation of the
correction factor C
dir,k
5.3 Test arrangement
The test method can be applied either on noise reducing devices installed alongside roads or on full-size
samples purposely assembled to be tested (indoors or outdoors) using the method described here.
5.3.1 Tests on purposely built full -size samples
For applications on full-size samples purposely built to be tested using the method described here, e.g. in an
outdoor test facility, the specimen shall be built as follows (see Figure 6):
— a part, composed of acoustic e
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