EN 1793-5:2025

SLOVENSKI STANDARD
01-februar-2026
Nadomešča:
SIST EN 1793-5:2016
SIST EN 1793-5:2016/AC:2018
Protihrupne ovire za cestni promet - Preskusna metoda za ugotavljanje akustičnih
lastnosti - 5. del: Bistvene značilnosti - Absorpcija zvoka v pogojih usmerjenega
zvočnega polja
Road traffic noise reducing devices - Test method for determining the acoustic
performance - Part 5: Intrinsic characteristics - Sound absorption under direct sound field
conditions
Lärmschutzvorrichtungen 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
Ta slovenski standard je istoveten z: EN 1793-5:2025
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.

EN 1793-5
EUROPEAN STANDARD
NORME EUROPÉENNE
December 2025
EUROPÄISCHE NORM
ICS 17.140.30; 93.080.30 Supersedes EN 1793-5:2016, EN 1793-
5:2016/AC:2018
English Version
Road traffic noise reducing devices - Test method for
determining the acoustic performance - Part 5: Intrinsic
characteristics - Sound absorption under direct sound field
conditions
Dispositifs de réduction du bruit du trafic routier - Lärmschutzvorrichtungen an Straßen - Prüfverfahren
Méthode d'essai pour la détermination de la zur Bestimmung der akustischen Eigenschaften - Teil
performance acoustique - Partie 5: Caractéristiques 5: Produktspezifische Merkmale - Schallabsorption in
intrinsèques - Absorption acoustique dans des gerichteten Schallfeldern
conditions de champ acoustique direct
This European Standard was approved by CEN on 17 November 2025.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 1793-5:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
Introduction . 6
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 8
4 Symbols and abbreviations . 14
5 Sound reflection index measurements . 16
5.1 General principle . 16
5.2 Measured quantity . 17
5.3 Test arrangement . 20
5.3.1 General. 20
5.3.2 Tests on purposely built full-size test specimens . 20
5.3.3 Installed road traffic noise reducing devices . 21
5.3.4 Inclined or curved road traffic noise reducing devices . 23
5.4 Measuring equipment . 26
5.4.1 Components of the measuring system . 26
5.4.2 Sound source . 27
5.4.3 Test signal . 27
5.5 Data processing . 28
5.5.1 Calibration . 28
5.5.2 Sample rate and filtering. 29
5.5.3 Background noise . 30
5.5.4 Signal subtraction technique . 31
5.5.5 Accurate alignment procedure . 32
5.5.6 Adrienne temporal window . 34
5.5.7 Placement of the Adrienne temporal window . 36
5.5.8 Maximum sampled area . 38
5.6 Positioning of the measuring equipment . 39
5.6.1 General. 39
5.6.2 Selection of the measurement positions . 39
5.6.3 Consideration of relevant and parasitic reflections. 47
5.6.4 Low-frequency limit . 50
5.6.5 Reflecting objects . 51
5.6.6 Safety considerations . 51
5.7 Test specimen surface and meteorological conditions . 51
5.7.1 Condition of the test specimen surface . 51
5.7.2 Wind. 51
5.7.3 Air temperature. 51
5.8 Single-number rating of sound absorption under a direct sound field DL . 51
RI
6 Measurement uncertainty . 52
7 Measuring procedure . 52
8 Test report . 53
Annex A (informative) Low-frequency limit and window width . 55
Annex B (normative) Measurement uncertainty . 60
Annex C (normative) Template of test report on sound reflection index of road traffic noise
reducing devices . 62
Annex D (normative) Indoor measurements for product qualification . 71
Bibliography . 72

European foreword
This document (EN 1793-5:2025) has been prepared by Technical Committee CEN/TC 226 “Road
equipment”, the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by June 2026, and conflicting national standards shall be
withdrawn at the latest by June 2026.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 1793-5:2016.
— the definitions from 3.1 to 3.8 have been updated to be in accordance with all other parts of the
series of standards;
— 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.
The EN 1793 series, under the general title Road traffic noise reducing devices — Test method for
determining the acoustic performance, consists of the following parts:
— Part 1: Intrinsic characteristics — Sound absorption under diffuse sound field conditions;
— Part 2: Intrinsic characteristics — Airborne sound insulation under diffuse sound field conditions;
— Part 3: Normalized traffic noise spectrum;
— Part 4: Intrinsic characteristics — Intrinsic sound diffraction;
— Part 5: Intrinsic characteristics — Sound absorption under direct sound field conditions;
— Part 6: Intrinsic characteristics — Airborne sound insulation under direct sound field conditions.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
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 1793-1:2025), 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 geometric envelope,
e, across the road formed by the barriers, 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 sound 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 1793-1:2025) 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 1793-1:2025
and direct sound field data, measured according to the method described in this document [6], [9], [17],
[18], [19], [23].
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.
(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
1 2
Key
r road surface
w width of open space
h1 developed length of the construction, e.g. cover, trench side, barrier or building
h developed length of the construction, e.g. cover, trench side, barrier or building
NOTE Figure 1 is not to scale.
Figure 1 — (not to scale) Sketch of the reverberant condition check in four cases
1 Scope
This document specifies 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.
This document is applicable to:
— the 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 test specimen section;
— the determination of the intrinsic characteristics of sound absorption of road traffic noise reducing
devices in actual use under direct sound field conditions;
— the comparison of design specifications with actual performance data after the completion of the
construction work;
— the verification of the long-term performance of road traffic noise reducing devices (with a repeated
application of the method).
This document does not apply to:
— the 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 between 200 Hz and 5 kHz, for qualification purposes. If it is not possible to get valid
measurement results over the whole frequency range indicated, the results are given in a restricted
frequency range, and the reasons for the restriction(s) are clearly reported.
For indoor measurements, see Annex D.
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, Road traffic noise reducing devices — Test method for determining the acoustic performance
— Part 3: Normalized traffic noise spectrum
EN 14389:2023, Road traffic noise reducing devices — Procedures for assessing long term performance
EN 61672-1, 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)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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 sound energy.
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 2 to entry: See Figures 3, 5 and 6.
Note 3 to entry: Microphones are numbered like in Figure 3.
3.12
reference height for the microphone grid
height h equal to half the height, h , of the road traffic noise reducing device under test: h = h /2
M B M B
Note 1 to entry: When the road traffic noise reducing device under test is not vertical, the microphone grid is
inclined so as to be parallel to the source and microphone reference surface. See 3.14 and Figure 8.
3.13
reference height for the sound source
height at which the sound source is placed
Note 1 to entry: For vertical road traffic noise reducing devices, h is equal to the reference height for the
S
microphone grid h . For inclined road traffic noise reducing devices, h is different from h . See 3.14, 3.15 and
M S M
Figure 8.
Note 2 to entry: For inclined road traffic noise reducing devices, the sound source position is in line with the
central microphone (microphone 5) of the microphone grid at a 1,50 m distance from the source and microphone
reference surface in the direction normal to it. See Figure 8.
Note 3 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 sound source h > 2 m, it is possible to have h = 2 m, accepting the corresponding
S S
low-frequency limitation. See 5.6.2 and 5.6.4.
Note 4 to entry: See Figures 2 and 4.
3.14
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, 7, 8, and 9.
3.15
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 distance of the source front panel to the
S
reference surface is d = 1,50 m
S
Note 1 to entry: For vertical road traffic noise reducing devices, See Figures 2 and 4. For inclined road traffic noise
reducing devices, See Figure 8.
3.16
measurement grid reference position
position of the measurement grid during the test
Note 1 to entry: the conditions and distances for a correct measurement grid 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.
3.17
reference loudspeaker-measurement grid distance
distance between the front panel of the loudspeaker and the central microphone (microphone 5) of the
measurement grid
Note 1 to entry: The reference loudspeaker-measurement grid distance is equal to d = 1,25 m (see Figures 2 and
SM
4).
3.18
free-field measurement for sound reflection index measurements
measurement taken with the loudspeaker and the measurement microphones in an acoustic free-field
in order to avoid reflections from any nearby object, including the ground and the noise reducing device
under test, keeping the same geometry as when measuring in front of the noise reducing device under
test
Note 1 to entry: See Figure 4.
3.19
maximum sampled area
surface area, projected on a front view of the road traffic noise reducing device under test for reflection
index measurements, which remains free of reflecting objects causing parasitic reflections
3.20
Adrienne temporal window
analysis window in the time domain to be used for the data processing according to the present
document
Note 1 to entry: The Adrienne temporal window is described in 5.5.6.
3.21
background noise
noise coming from sources other than the sound source emitting the test signal
3.22
signal-to-noise ratio
S/N 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)
3.23
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.
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 surface 2 reference heights h and h [m]
S M
3 loudspeaker front panel 4 distance between the loudspeaker front panel and
the reference surface, dS [m]
distance between the loudspeaker front distance between the measurement grid and the
5 6
panel and the measurement grid, d [m] reference surface, d [m]
SM 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 a
vertical road traffic noise reducing device
Key
1 road traffic noise reducing device height h [m] 2 reference height h [m]
B S
3 orthogonal spacing between two subsequent M1…M9 microphone positions
microphones s [m]
Figure 3 — (not to scale) Measurement grid for sound reflection index measurements in front of
a vertical road traffic noise reducing device (sound source side)

Key
1 reference heights h and h [m] 2 distance between the loudspeaker front panel and the
S M
measurement grid d [m]
SM
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 of a vertical road traffic noise reducing
device
4 Symbols and abbreviations
For the purposes of this document, the symbols and abbreviations in Table 1 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 test specimen 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
b Width of a portion of material of the test specimen m
m
c Speed of sound in air m/s
C Correction factor for the geometrical divergence at the k-th measurement -
geo,k
point
C Correction factor for the sound source directivity at the k-th measurement -
dir,k
point
C Correction factor for changes in the sound source gain at the k-th -
gain,k
measurement point
d Distance from the source and microphone reference surface to the m
M
measurement grid; it is equal to d = 0,25 m
M
d 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 Distance from the front panel of the loudspeaker to the measurement grid; it is m
SM
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-th 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 5.5.5)
Δt Time delay gap between the arrival of direct sound at microphone k (k ≠ 5) s
k5
Symbol or Designation Unit
abbreviation
and microphone 5
Δtk Time delay gap between the arrival of direct and reflected sound at s
microphone k
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
f Low-frequency limit of sound reflection index measurements Hz
min
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 for the microphone grid m
M
hS Reference height for the sound source m
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) -
h (t) Incident reference component of the impulse response taken in front of the -
i,k,FF
test specimen at the k-th measurement point (before the signal subtraction)
h (t) Residual incident reference component of the impulse response taken in front -
i,k,RES
of the test specimen at the k-th measurement point (after the signal
subtraction)
k Index of the k-th measurement point (k = 1 … nj) -
k Coverage factor -
p
k Constant used for the anti-aliasing filter -
f
L Relative A-weighted sound pressure level of the normalized traffic noise dB
i
spectrum in the i-th one-third octave band (see EN 1793-3)
L Spatial period length of a non-homogeneous noise reducing device m
p
n Number of microphone positions 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
Symbol or Designation Unit
abbreviation
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
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) Time window (Adrienne temporal window) for the incident reference -
i,k
component of the free-field impulse response at the k-th measurement point
w (t) Time window (Adrienne temporal window) for the reflected component at the -
r,k
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 surfaces other than the tested device can be identified from
their delay time and rejected.
For measurements carried out indoors or under geometric site conditions that may create a
reverberant field on the emission or reception side (tunnel exits, building facades, etc.), the
requirements of Annex D shall be verified.
5.2 Measured quantity
The expression used to compute the reflection index RI as a function of frequency, in one-third octave
bands, is:

n  
F h ()t ⋅ w ()t df
j
rk,,rk
∫
 
1 ∆ fj
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
∫
 
∆ fj

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 test specimen
r,k
at the k-th measurement point;
w (t) is the time window (Adrienne temporal window) for the incident reference
i,k
component of 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-
r,k
th 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);
is the width of the j-th one-third octave frequency band;
∆ f
j
k is the index of the k-th microphone position (k = 1, ., n ); see Figure 3;
j
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 at the k-th measurement point to account for a change in the
gain,k g
amplification settings of the loudspeaker and in the sensitivity settings of the
individual microphones when changing the measurement configuration from free field
to in front of the test specimen 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 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
Table 2 — Distances d , d and correction factors C for a plane reference surface
geo,k
i,k r,k
k d d C
i,k r,k geo,k
m m
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, also considering 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 (,tα )⋅ w (t) df
ik,,k ik
∫
 
∆ f
j
Cf()∆ = (3)
dri ,k j
 
F h (,tβ )⋅ 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
k
to microphone 5 and the line connecting the centre of the front panel of the
loudspeaker to microphone k (see Figure 5.a);
β is the angle between the line connecting the centre of the front panel of the loudspeaker
k
to 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 5.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
i,k
front panel of the loudspeaker;
w (t) is the time window (Adrienne temporal window) for the incident reference component
i,k
of the free-field impulse response at the k-th 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);
is the width of the j-th one-third octave frequency band;

∆ f
j
k is the microphone number according to Figure 3 (k = 1, ., n ).
j
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)
i,k
from 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 with an Adrienne
window of length 7,9 ms. The sound source directivity correction factors shall be measured only once
for each sound source, assuming that the source directivity patterns do not change. For the sake of
accuracy, they may be measured again from time to time (e.g. once a year).
(a) top view of microphone positions 4, 5, and 6, (b) front view of the nine microphone
angles α and β for microphone 4 and the positions (white circles) and the nine
4 4
point, at a distance d from the loudspeaker positions where the specular reflection travel
i,4
centre plate, where measurements to get the path of the sound emitted by the loudspeaker
correction factor C are done intersect the plane of the measurement grid
dir,4
(black circles)
NOTE to Figure 5.a  Microphone positions 4, 5, and 6 are identified with white circles. The point, at a distance
d from the loudspeaker centre plate, where measurements to get the correction factor C are done is identified
i,4 dir,4
with a grey circle.
Key
1 loudspeaker 2 test specimen
3 distance from the measurement grid to the 4 microphone 4
source and microphone reference surface,
dM [m]
5 microphone 5 6 microphone 6
7 orthogonal spacing between two subsequent 8 distance d from the loudspeaker centre plate to
i,4
microphones, s [m] microphone 4, where measurements to get the
correction factor C shall be done [m]
dir,4
9 angle α between the line connecting the ce
...