EN 16272-5:2023

SLOVENSKI STANDARD
01-februar-2024
Železniške naprave - Infrastruktura - Protihrupne ovire in pripadajoče naprave, ki
vplivajo na širjenje zvoka v zraku - Preskusna metoda za ugotavljanje akustičnih
lastnosti - 5. del: Posebne karakteristike - Absorpcija zvoka pri usmerjenem
zvočnem polju
Railway applications - Infrastructure - Noise barriers and related devices acting on
airborne sound propagation - Test method for determining the acoustic performance -
Part 5: Intrinsic characteristics - Sound absorption under direct sound field conditions
Bahnanwendungen - Oberbau - Lärmschutzwände und verwandte Vorrichtungen zur
Beeinflussung der Luftschallausbreitung - Prüfverfahren zur Bestimmung der
akustischen Eigenschaften - Teil 5: Intrinsische Merkmale - In-situ-Werte zur
Schallreflexion in gerichteten Schallfeldern
Applications ferroviaires - Voie - Dispositifs de réduction du bruit - Méthode d'essai pour
la détermination des performances acoustiques - Partie 5 : Caractéristiques intrinsèques
- Absorption acoustique dans des conditions de champ acoustique direct
Ta slovenski standard je istoveten z: EN 16272-5:2023
ICS:
17.140.30 Emisija hrupa transportnih Noise emitted by means of
sredstev transport
93.100 Gradnja železnic Construction of railways
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 16272-5
EUROPEAN STANDARD
NORME EUROPÉENNE
November 2023
EUROPÄISCHE NORM
ICS 93.100 Supersedes CEN/TS 16272-5:2014
English Version
Railway applications - Infrastructure - Noise barriers and
related devices acting on airborne sound propagation -
Test method for determining the acoustic performance -
Part 5: Intrinsic characteristics - Sound absorption under
direct sound field conditions
Applications ferroviaires - Infrastructure - Dispositifs Bahnanwendungen - Oberbau - Lärmschutzwände und
de réduction du bruit - Méthode d'essai pour la verwandte Vorrichtungen zur Beeinflussung der
détermination de la performance acoustique - Partie 5 : Luftschallausbreitung - Prüfverfahren zur Bestimmung
Caractéristique intrinsèques - Absorption acoustique der akustischen Eigenschaften - Teil 5:
dans des conditions de champ acoustique direct Produktspezifische Merkmale - In-situ-Werte zur
Schallreflexion in gerichteten Schallfeldern
This European Standard was approved by CEN on 8 October 2023.

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
© 2023 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 16272-5:2023 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
Introduction . 4
1 Scope . 8
2 Normative references . 8
3 Terms, definitions, symbols and abbreviations . 9
3.1 Terms and definitions . 9
3.2 Symbols and abbreviations . 13
4 Sound reflection index measurements . 15
4.1 General principle . 15
4.2 Measured quantity . 16
4.3 Test arrangement . 19
4.3.1 General . 19
4.3.2 Tests on purposely built full -size samples . 19
4.3.3 Installed noise barriers and related devices . 19
4.3.4 Inclined or curve noise barriers and related devices . 21
4.4 Measuring equipment . 24
4.4.1 Components of the measuring system . 24
4.4.2 Sound source . 25
4.4.3 Test signal . 25
4.5 Data processing . 26
4.5.1 Calibration . 26
4.5.2 Sample rate and filtering . 27
4.5.3 Background noise . 28
4.5.4 Signal subtraction technique . 29
4.5.5 Accurate alignment procedure . 29
4.5.6 Adrienne temporal window . 31
4.5.7 Placement of the Adrienne temporal window . 33
4.5.8 Maximum sampled area. 36
4.6 Positioning of the measuring equipment . 36
4.6.1 General . 36
4.6.2 Selection of the measurement positions. 37
4.6.3 Consideration of relevant and parasitic reflections . 44
4.6.4 Low-frequency limit . 47
4.6.5 Reflecting objects . 48
4.6.6 Safety considerations. 48
4.7 Sample surface and meteorological conditions . 48
4.7.1 Condition of the sample surface . 48
4.7.2 Wind . 48
4.7.3 Air temperature . 48
4.8 Single-number rating of sound absorption under a direct sound field DL . 48
RI
5 Measurement uncertainty . 48
6 Measuring procedure . 49
7 Test report . 50
Annex A (informative)  Low-frequency limit and window width . 51
A.1 General . 51
Annex B (informative)  Measurement uncertainty . 55
B.1 General . 55
B.2 Measurement uncertainty based upon reproducibility data . 55
B.3 Standard deviation of repeatability and reproducibility of the sound reflection index . 55
Annex C (normative)  Template of test report on sound reflection index of railway noise
barriers and related devices acting on airborne sound propagation . 57
C.1 General . 57
C.2 Test setup (example) . 60
C.3 Test object and test situation (example) . 61
C.4 Test Results (example) . 63
C.4.1 Part 1 – Results in tabular form . 63
C.4.2 Part 2 – Results in graphic form. 64
C.5 Uncertainty (example) . 64
Annex D (informative) Indoor measurements for product qualification . 66
D.1 General . 66
D.2 Parasitic reflections . 66
D.3 Reverberation time of the room . 66
Bibliography . 67

European foreword
This document (EN 16272-5:2023) has been prepared by Technical Committee CEN/TC 256 “Railway
applications”, the secretariat of which is held by DIN.
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 May 2024 and conflicting national standards shall be withdrawn at
the latest by May 2024.
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 CEN/TS 16272-5:2014.
With respect to the superseded document, the following changes have been done:
— the references have been updated;
— the rotating loudspeaker/microphone assembly has been replaced by a loudspeaker and a 9-microphone
square array (the measurement grid);
— the definition of RI has been changed;
— the geometrical divergence correction factor has been changed;
— a new correction factor for sound source directivity has been introduced;
— a new correction factor for gain mismatch has been introduced;
— the impulse response alignment for signal subtraction has been specified in more detail;
— the lowest reliable one-third frequency band has been better defined (Annex A);
— the single number rating DL is now reported with one decimal digit;
RI
— the way to evaluate the uncertainty of the measurement method from reproducibility data has been
introduced (Annex B);
— a detailed example is given, including the evaluation of measurement uncertainty (Annex C);
— a new annex on indoor measurements has been added (Annex D).
EN 16272-5 is part of a series and should be read in conjunction with the other parts. All parts are listed
below:
EN 16272-1, Railway applications — Infrastructure — Noise barriers and related devices acting on airborne
sound propagation — Test method for determining the acoustic performance — Part 1: Intrinsic characteristics
- Sound absorption under diffuse sound field conditions
EN 16272-2, Railway applications — Infrastructure — Noise barriers and related devices acting on airborne
sound propagation — Test method for determining the acoustic performance — Part 2: Intrinsic characteristics
- Airborne sound insulation under diffuse sound field conditions (the present document)
EN 16272-3-1, Railway applications — Infrastructure — Noise barriers and related devices acting on airborne
sound propagation — Test method for determining the acoustic performance — Part 3-1: Normalized railway
noise spectrum and single number ratings for diffuse sound field applications
EN 16272-3-2, Railway applications — Infrastructure — Noise barriers and related devices acting on airborne
sound propagation — Test method for determining the acoustic performance — Part 3-2: Normalized railway
noise spectrum and single number ratings for direct sound field applications
EN 16272-4, Railway applications — Track — Noise barriers and related devices acting on airborne sound
propagation — Test method for determining the acoustic performance — Part 4: Intrinsic characteristics - In
situ values of sound diffraction under direct sound field conditions
EN 16272-5, Railway applications — Infrastructure — Noise barriers and related devices acting on airborne
sound propagation — Test method for determining the acoustic performance — Part 5: Intrinsic characteristics
- Sound absorption under direct sound field conditions
EN 16272-6, Railway applications — Infrastructure — Noise barriers and related devices acting on airborne
sound propagation — Test method for determining the acoustic performance — Part 6: Intrinsic characteristics
- Airborne sound insulation under direct sound field conditions
CEN/TS 16272-7, Railway applications — Track — Noise barriers and related devices acting on airborne sound
propagation — Test method for determining the acoustic performance — Part 7: Extrinsic characteristics - In
situ values of insertion loss
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 organizations 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 reflection of
noise barriers and related devices acting on airborne sound propagation designed for railways in non-
reverberant conditions (a measure of intrinsic performance). 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
noise barriers are installed. The method can be applied without damaging the surface.
The method can be used to qualify products to be installed along railways as well as to verify the compliance
of installed noise barriers and related devices acting on airborne sound propagation to design specifications.
Regular application of the method can be used to verify the long-term performance of noise barriers and
related devices acting on airborne sound propagation. 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 directly comparable with the results
obtained under diffuse sound field conditions (e.g. EN 16272-1), mainly because the present method uses a
directional sound field, not a diffuse sound field. The test method specified in the present document should
not be used to determine the intrinsic characteristics of sound absorption of noise barriers and related devices
acting on airborne sound propagation 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
railway formed by the device under test, trench sides or buildings (the envelope does not include the rail
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, called reflection index, to define the sound reflection in front of a
noise barrier, and then calculate a single-number rating for sound absorption from it, while the measurements
under diffuse sound field conditions (according to EN 16272-1) give 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 16272-1 and direct sound field
data, measured according to the method specified in this document [6], [9], [17], [18], [19], [20].
NOTE This method can be used to qualify noise barriers and related devices acting on airborne sound propagation
for other applications, e.g. to be installed nearby industrial sites. In this case the single-number ratings (see
EN 16272-3-2) is calculated using an appropriate spectrum.

a) Partial cover on both sides of the railway; b) Partial cover on one side of the railway;
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
e) Train passing close to a noise barrier; f) Train passing close to a platform at the
station. envelope, e = w+h +h
1 2
envelope, e = w+h +h
1 2
Key
r rail surface
w width of open space
h1 Developed length of element, e.g. cover, trench side, barrier or building
h2 Developed length of element, 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 some cases
1 Scope
This document describes a test method for measuring a quantity representative of the intrinsic characteristics
of sound absorption from railway noise barriers and related devices acting on airborne sound propagation,
the sound reflection index RI, 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 barriers and related devices
acting on airborne sound propagation to be installed along railways, to be measured either on typical
installations alongside railways or on a relevant sample section;
— determination of the intrinsic characteristics of sound absorption of noise barriers and related devices
acting on airborne sound propagation 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 noise barriers and related devices acting on airborne sound
propagation (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 noise barriers and related devices
acting on airborne sound propagation 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 are given in a restricted frequency range and the reasons of the
restriction(s) are 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 16272-3-2, Railway applications - Infrastructure - Noise barriers and related devices acting on airborne
sound propagation - Test method for determining the acoustic performance - Part 3-2: Normalized railway noise
spectrum and single number ratings for direct field applications
EN 16951-1, Railway applications - Track - Noise barriers and related devices acting on airborne sound
propagation - Procedures for assessing long term performance - Part 1: Acoustic characteristics
EN 61672-1, Electroacoustics - Sound level meters - Part 1: Specifications
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
3 Terms, definitions, symbols and abbreviations
3.1 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:
— IEC Electropedia: available at https://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp/
NOTE For the purpose of this document, the following definitions take precedence over other definitions from the
above websites.
3.1.1
noise barrier
noise reducing device, which obstructs the direct transmission of airborne sound emanating from railways
and which will typically span between posts and also may overhang the railway
Note 1 to entry: Noise barriers are generally made of acoustic and structural elements (see 3.1.3 and 3.1.4).
3.1.2
cladding
noise reducing device, which is attached to a wall or other structure and reduces the amount of sound
reflected
Note 1 to entry: Claddings are generally made of acoustic and structural elements (see 3.1.3 and 3.1.4).
3.1.3
acoustic element
element whose primary function is to provide the acoustic performance of the device
3.1.4
structural element
element whose primary function is to support or hold in place acoustic elements
3.1.5
added device
added component that influences the acoustic performance of the original noise-reducing device (acting
primarily on the diffracted energy)
Note 1 to entry: In some noise barriers, the acoustic function and the structural function cannot be clearly separated
and attributed to different components.
3.1.6
railway side exposure
the use of the product as a noise reducing device installed alongside railways
3.1.7
sound reflection index
quantity representing the amount of sound not absorbed by the device under test, specified by Formula (1)
Note 1 to entry: This is the result of a test according to the present document.
3.1.8
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 4.6 and Figure 3.
Note 3 to entry: Microphones are numbered like in Figure 3.
3.1.9
reference height
height h equal to half the height, h , of the noise barrier 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 4.5.7 and 4.6.4).
Note 2 to entry: See Figures 2 and 3.
3.1.10
(source and microphone) reference surface for sound reflection index measurements
ideal, smooth surface facing the sound source side of the noise barrier 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 noise barriers, the reference surface is a vertical plane. For inclined and
flat noise barriers, the reference surface is a plane with the same inclination. For curve and flat noise barriers, the
reference surface is a curve surface with the same curvature
Note 2 to entry: See Figures 2, 7, 8, and 9.
3.1.11
source reference position
position facing the side to be exposed to noise when the device is in place, located at the reference height h
S
and placed so that the horizontal distance of the source front panel to the reference surface is d = 1,50 m
S
Note 1 to entry: See Figures 2 and 3.
3.1.12
measurement grid reference position
position of the measurement grid compliant with all the following conditions:
i) the measurement grid is on the noise barrier side to be exposed to noise when the device is in place;
ii) the central microphone (microphone n. 5) is located at the reference height h ;
S
iii) the shortest distance of the central microphone to the reference surface is d = 0,25 m
M
Note 1 to entry: For flat noise barriers, see Figures 2, and 3. For non-flat noise barriers, see Figure 7. For inclined or
curved noise barriers, see Figures 8 and 9.
3.1.13
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).
3.1.14
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 device under test
Note 1 to entry: See Figure 4.
3.1.15
maximum sampled area
surface area, projected on a front view of the device under test for reflection index measurements, which must
remain free of reflecting objects causing parasitic reflections
3.1.16
Adrienne temporal window
composite temporal window having a leading edge with a left-half Blackman-Harris shape and a fixed length
of 0,5 ms, followed by a flat portion and a trailing edge having a right-half Blackman-Harris shape, so that the
lengths of the flat portion and the right-half Blackman-Harris portion have a ratio of 7/3
Note 1 to entry: This type of window is specified in 4.5.6.
3.1.17
background noise
noise coming from sources other than the sound source emitting the test signal
3.1.18
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)
3.1.19
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 height hS [m]
3 loudspeaker front panel 4 distance between the loudspeaker front panel and the
reference surface, d [m]
S
5 distance between the loudspeaker front panel 6 distance between the measurement grid and the
and the measurement grid, dSM [m] reference surface, dM [m]
7 measurement grid 8 noise barrier height, h [m]
B
Figure 2 — (not to scale) Sketch of the sound source and the measurement grid in front of the noise
barrier under test for sound reflection index measurements

Key
1 noise barrier height h [m] 2 reference height h [m]
B S
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 h [m] 2 distance between the loudspeaker front panel and the measurement grid d [m]
S 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
3.2 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
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 Depth of the surface structure of the sample under test m
s
b Width of a portion of material of the sample under test m
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
Symbol or Designation Unit
abbreviation
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 index dB
RI
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 4.5.5)
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 s
k
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
fs Sample rate Hz
f Cut-off frequency of the anti-aliasing filter Hz
co
h Height of the device under test 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
h (t) Incident reference component of the impulse response taken in front of the -
i,k,FF
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 -
i,k,RES
of the sample under test at the k-th measurement point (after the signal
subtraction)
j Index of the j-th one-third octave frequency band (between 100 Hz and 5 kHz) -
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
Symbol or Designation Unit
abbreviation
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 4.5.5)
r Radius of the maximum sampled area at normal incidence m
R Reduction factor dB
sub
RIj Sound reflection index in the j-th one-third octave frequency band -
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) Reference free-field component time window (Adrienne temporal window) at -
i,k
the k-th measurement point
w (t) Time window (Adrienne temporal window) for the reflected component at the -
r,k
k-th measurement point
4 Sound reflection index measurements
4.1 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.
4.2 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 ∆f

j
RI ⋅C ⋅C∆⋅f C∆f
( ) ( )

j ∑ 2 geo,,k dir k j gain,k g
n
k=1
j 
F h (t)⋅ w (t) df
i,,k i k
∫ 
∆f
j

(1)
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;
wi,k(t) is the time window (Adrienne temporal window) for the incident reference 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-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);
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, ., 9);
n is the number of microphone positions on which to average (n ≥ 6; see 4.6.2);
j j
C is the correction factor for geometrical divergence at the k-th measurement point;
geo,k
Cdir,k(Δfj) is the correction factor for sound source directivity at the k-th measurement point.
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 4.5.1 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 =
 
geo,k
 
d
i,k
 
(2)
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.
i,k r,k geo,k
Table 2 — Distances d , d and correction factors C for a plane reference surface
i,k r,k geo,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
i,,k k i k
∫ 
∆f
j
Cf∆ =
( )
dir,k j 2
Fh t,β ⋅ w t df
( ) ()
i,,k k i k
∫ 
∆f
j
(3)
where
α is the angle between the line connecting the centre
...