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

The present document describes a test method for measuring a quantity representative of the intrinsic characteristics of sound reflection from road noise reducing devices: the reflection index.
The test method is intended for the following applications:
- determination of the intrinsic characteristics of sound reflection 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 in situ intrinsic characteristics of sound reflection of noise reducing devices in actual use;
- comparison of design specifications with actual performance data after the completion of the construction work;
- verification of the long-term performance of noise reducing devices (with a repeated application of the method).
The test method is not intended for the following applications:
- determination of the intrinsic characteristics of sound reflection of noise reducing devices to be installed in reverberant conditions, e.g. inside tunnels or deep trenches.
Results are expressed as a function of frequency, in one-third octave bands between 100 Hz and 5 kHz. If it is not possible to get valid measurements results over the whole frequency range indicated, the results shall be given in a restricted frequency range and the reasons of the restriction(s) shall be clearly reported.

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

Protihrupne ovire za cestni promet - Preskusna metoda za ugotavljanje akustičnih lastnosti - 5. del: Bistvene lastnosti - Terenske vrednosti odboja zvoka z uporabo usmerjenega zvočnega polja

Ta dokument opisuje preskusno metodo za merjenje količine, ki predstavlja bistvene lastnosti na področju odboja zvoka od protihrupnih ovir za cestni promet: indeks odboja.
Preskusna metoda je namenjena:
– ugotavljanju bistvenih lastnosti na področju odboja zvoka od obcestnih protihrupnih ovir, ki se merijo na običajnih mestih namestitve ob cesti ali na ustreznem vzorčnem delu;
– ugotavljanju bistvenih lastnosti na področju odboja zvoka od protihrupnih ovir med dejansko uporabo na mestu uporabe;
– primerjavi specifikacij zasnove s podatki o dejanskih lastnostih po koncu izgradnje;
– preverjanje dolgoročnih lastnosti protihrupnih ovir (z večkratno izvedbo metode).
Preskusna metoda ni namenjena:
– ugotavljanju bistvenih lastnostih za odboj zvoka od protihrupnih naprav za namestitev v odmevnih pogojih, npr. v predorih.
Rezultati so izraženi kot funkcija frekvence v tretjinskih oktavnih pasovih med 100 Hz in 5 kHz. Če ni mogoče dobiti veljavnih rezultatov meritev za celo opredeljeno frekvenčno območje, se rezultati navedejo za omejeno frekvenčno območje, razlogi za omejitev območja pa se jasno opredelijo.

General Information

Status
Published
Public Enquiry End Date
30-Jul-2014
Publication Date
16-Jun-2016
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
08-Apr-2016
Due Date
13-Jun-2016
Completion Date
17-Jun-2016

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SLOVENSKI STANDARD
SIST EN 1793-5:2016
01-julij-2016
1DGRPHãþD
SIST-TS CEN/TS 1793-5:2004
3URWLKUXSQHRYLUH]DFHVWQLSURPHW3UHVNXVQDPHWRGD]DXJRWDYOMDQMHDNXVWLþQLK

ODVWQRVWLGHO%LVWYHQHODVWQRVWL7HUHQVNHYUHGQRVWLRGERMD]YRND]XSRUDER

XVPHUMHQHJD]YRþQHJDSROMD
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: EN 1793-5:2016
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
SIST EN 1793-5:2016 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 1793-5:2016
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SIST EN 1793-5:2016
EN 1793-5
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2016
EUROPÄISCHE NORM
ICS 17.140.30; 93.080.30 Supersedes CEN/TS 1793-5:2003
English Version
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

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 - In-situ-Werte der

intrinsèques - Valeurs in situ de réflexion acoustique Schallreflexion in gerichteten Schallfeldern

dans des conditions de champ acoustique direct
This European Standard was approved by CEN on 23 January 2016.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2016 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 1793-5:2016 E

worldwide for CEN national Members.
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SIST EN 1793-5:2016
EN 1793-5:2016 (E)
Contents

European foreword ................................................................................................................................................................ 4

Introduction ............................................................................................................................................................................. 6

1 Scope ............................................................................................................................................................................. 8

2 Normative references ............................................................................................................................................. 8

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 .................................................................................................................................................. 18

5.4 Measuring equipment ......................................................................................................................................... 23

5.4.1 Components of the measuring system ........................................................................................................... 23

5.4.2 Sound source ........................................................................................................................................................... 24

5.4.3 Test signal ................................................................................................................................................................ 24

5.5 Data processing ...................................................................................................................................................... 25

5.5.1 Calibration ............................................................................................................................................................... 25

5.5.2 Sample rate .............................................................................................................................................................. 26

5.5.3 Background noise ................................................................................................................................................. 27

5.5.4 Signal subtraction technique ............................................................................................................................ 27

5.5.5 Adrienne temporal window .............................................................................................................................. 30

5.5.6 Placement of the Adrienne temporal window ............................................................................................ 32

5.5.7 Low frequency limit and sample size ............................................................................................................. 33

5.6 Positioning of the measuring equipment ..................................................................................................... 35

5.6.1 Maximum sampled area...................................................................................................................................... 35

5.6.2 Selection of the measurement positions....................................................................................................... 35

5.6.3 Reflecting objects .................................................................................................................................................. 42

5.6.4 Safety considerations........................................................................................................................................... 42

5.7 Sample surface and meteorological conditions ......................................................................................... 42

5.7.1 Condition of the sample surface ...................................................................................................................... 42

5.7.2 Wind ........................................................................................................................................................................... 42

5.7.3 Air temperature ..................................................................................................................................................... 42

5.8 Single-number rating of sound reflection DL ........................................................................................... 42

5.9 Measurement uncertainty ................................................................................................................................. 43

5.10 Measuring procedure .......................................................................................................................................... 43

5.11 Test report ............................................................................................................................................................... 44

Annex A (informative) Measurement uncertainty ................................................................................................ 46

A.1 General ...................................................................................................................................................................... 46

A.2 Measurement uncertainty based upon reproducibility data ................................................................ 46

A.3 Standard deviation of repeatability and reproducibility of the sound reflection index ............. 46

Annex B (informative) Template of test report on sound reflection of road noise barriers ................. 48

B.1 Overview .................................................................................................................................................................. 48

B.2 Test setup (example) ........................................................................................................................................... 50

B.3 Test object and test situation (example) ...................................................................................................... 51

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SIST EN 1793-5:2016
EN 1793-5:2016 (E)

B.4 Test Results (example) ........................................................................................................................................ 53

B.4.1 Part 1 – Results in tabular form ........................................................................................................................ 53

B.4.2 Part 2 – Results in graphic form........................................................................................................................ 54

B.5 Uncertainty (example) ......................................................................................................................................... 54

Annex C (informative) Near field to far field relationship .................................................................................. 56

Bibliography ........................................................................................................................................................................... 57

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SIST EN 1793-5:2016
EN 1793-5:2016 (E)
European foreword

This document (EN 1793-5:2016) has been prepared under the direction of Technical Committee

CEN/TC 226 “Road equipment”, by Working Group 6 “Anti-noise devices”, the secretariat of which is held by

AFNOR.
This document supersedes CEN/TS 1793-5:2003.

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 September 2016, and conflicting national standards shall be

withdrawn at the latest by September 2016.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.

With respect to the superseded document, the following changes have been done:

— 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 described in more detail;

— the lowest reliable one-third frequency band has been better defined;

— the way to evaluate the uncertainty of the measurement method from reproducibility data has been

introduced (Annex A);
— a detailed example is given (Annex B);

— information on the near-field to far-field relationship has been added (Annex C).

It should be read in conjunction with:

EN 1793-1, Road traffic noise reducing devices - Test method for determining the acoustic performance –

Part 1: Intrinsic characteristics of sound absorption under diffuse sound field conditions

EN 1793-2, Road traffic noise reducing devices - Test method for determining the acoustic performance –

Part 2: Intrinsic characteristics of airborne sound insulation under diffuse sound field conditions

EN 1793-3, Road traffic noise reducing devices - Test method for determining the acoustic performance –

Part 3: Normalized traffic noise spectrum

EN 1793-4, Road traffic noise reducing devices - Test method for determining the acoustic performance – Part

4: Intrinsic characteristics – In situ values of sound diffraction

EN 1793-6, Road traffic noise reducing devices - Test method for determining the acoustic performance – Part

6: Intrinsic characteristics – In situ values of airborne sound insulation under direct sound field conditions

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SIST EN 1793-5:2016
EN 1793-5:2016 (E)

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, Former Yugoslav Republic of Macedonia, France, Germany,

Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,

Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.

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SIST EN 1793-5:2016
EN 1793-5:2016 (E)
Introduction

This document describes a test method for determining the intrinsic characteristics of sound reflection of

noise reducing devices designed for roads in non-reverberant conditions (a measure of intrinsic

performance). It can be applied in situ, i.e. where the noise reducing devices are installed. The method can be

applied without damaging the surface.

The method can be used to qualify products to be installed along roads as well as to verify the compliance of

installed noise reducing 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 measurements results of this method for sound reflection are not directly comparable with the results

of the laboratory method (e.g. EN 1793-1), mainly because the present method uses a directional sound

field, while the laboratory method assumes a diffuse sound field. The test method described in the present

document should not be used to determine the intrinsic characteristics of sound reflection of 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, called reflection index, to define the sound reflection in front of a

noise reducing device, while the laboratory method gives a sound absorption coefficient. Laboratory values

of the sound absorption coefficient can be converted to conventional values of a reflection coefficient taking

the complement to one. In this case, research studies suggest that some correlation exists between

laboratory data, measured according to EN 1793-1 and field data, measured according to the method

described in the present document [7], [10], [20], [21].

This method may 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 should be calculated using an appropriate spectrum.

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SIST EN 1793-5:2016
EN 1793-5:2016 (E)

(a) Partial cover on both sides of the road; envelope, (b) Partial cover on one side of the road; envelope,

e = w+h +h . e = w+h .
1 2 1

(c) Deep trench; envelope, e = w+h +h . (d) Tall barriers or buildings; envelope, e = w+h +h .

1 2 1 2
Key
r road surface;
w width of open space
NOTE Figure 1 is not to scale.
Figure 1 —Sketch of the reverberant condition check in four cases
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SIST EN 1793-5:2016
EN 1793-5:2016 (E)
1 Scope

This European Standard describes a test method for measuring a quantity representative of the intrinsic

characteristics of sound reflection from road noise reducing devices: the reflection index.

The test method is intended for the following applications:

— determination of the intrinsic characteristics of sound reflection 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 in situ intrinsic characteristics of sound reflection of noise reducing devices in

actual use;

— comparison of design specifications with actual performance data after the completion of the

construction work;

— verification of the long term performance of noise reducing devices (with a repeated application of the

method).
The test method is not intended for the following applications:

— determination of the intrinsic characteristics of sound reflection of noise reducing devices to be

installed in reverberant conditions, e.g. inside tunnels or deep trenches.

Results are expressed as a function of frequency, in one-third octave bands between 100 Hz and 5 kHz. If it

is not possible to get valid measurements results over the whole frequency range indicated, the results

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, in whole or in part, are normatively referenced in this document and are

indispensable for its application. 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 61672-1, Electroacoustics – Sound level meters – Part 1: Specifications (IEC 61672-1)

ISO/IEC Guide 98-3, 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
noise reducing device (NRD)

device that is designed to reduce the propagation of traffic noise away from the road environment. This may

be a noise barrier, cladding, a road cover or an added device. These devices may include both acoustic and

structural elements
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SIST EN 1793-5:2016
EN 1793-5:2016 (E)
3.2
noise barrier

noise reducing device, which obstructs the direct transmission of airborne sound emanating from road

traffic
3.3
acoustic element

element whose primary function is to provide the acoustic performance of the device

3.4
structural element
element whose primary function is to support or hold in place acoustic elements
3.5
cladding

noise-reducing device, which is attached to a wall or other structure and reduces the amount of sound

reflected
3.6
cover
noise-reducing device, which either spans or overhangs the highway
3.7
added device

added component that influences the acoustic performance of the original noise-reducing device (acting

primarily on the diffracted energy)
3.8
roadside exposure
the use of the product as a noise reducing device installed alongside roads
3.9
sound reflection index
quantity, resulting from a sound reflection test, described by Formula (1)
3.10
measurement grid for sound reflection index measurements

vertical 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 Figure 3 and 5.6.
Note 3 to entry Microphones are numbered like in Figure 3.b.
3.11
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 h = h /2, it is possible to have h = 2 m, accepting the corresponding low

S B S
frequency limitation (see 5.5.7).
Note 2 to entry: See Figures 2 and 3.
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SIST EN 1793-5:2016
EN 1793-5:2016 (E)
3.12
(source and microphone) reference plane for sound reflection index measurements

plane facing the sound source side of the noise reducing device and touching the most protruding parts of

the device under test within the tested area
Note 1 to entry See Figures 2 and 4.
3.13
source reference position

position facing the side to be exposed to noise when the device is in place, located at the reference height h

and placed so that the horizontal distance of the source front panel to the reference plane is d = 1,50 m

Note 1 to entry See Figures 2 and 4.
3.14
measurement grid reference position

position of the measurement grid compliant with all the following conditions: i) the measurement grid is

vertical; ii) the measurement grid is on the noise reducing device side to be exposed to noise when the

device is in place; iii) the central microphone (microphone n. 5) is located at the reference height h ; iv) the

horizontal distance of the central microphone to the reference plane is d = 0,25 m; v) the line passing

through the centre plate of the loudspeaker and the central microphone is horizontal

Note 1 to entry See Figures 2, 3 and 4.
3.15
reference loudspeaker-measurement grid distance

distance between the front panel of the loudspeaker and the central microphone (microphone n. 5) of the

measurement grid (kept in vertical position)

Note 1 to entry The reference loudspeaker-measurement grid distance is equal to d = 1,25 m (see Figures 2 and

4).
3.16
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 5.
3.17
maximum sampled area

surface area, projected on a front view of the noise reducing device under test for reflection index

measurements, which must remain free of reflecting objects causing parasitic reflections

3.18
Adrienne temporal window
composite temporal window described in 5.5.5
3.19
background noise
noise coming from sources other than the sound source emitting the test signal
3.20
signal-to-noise ratio, S/N

difference in decibels between the level of the test signal and the level of the background noise at the

moment of detection of the useful event (within the Adrienne temporal window)
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EN 1793-5:2016 (E)
3.21
impulse response

time signal at the output of a system when a Dirac function is applied to the input. 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 1 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 plane 2 Reference height h [m]
3 Loudspeaker front panel 4 Distance between the loudspeaker front panel and
the reference plane d [m]

5 Distance between the loudspeaker front 6 Distance between the measurement grid and the

panel and the measurement grid d [m] reference plane d [m]
SM M
7 Measurement grid 8 Noise reducing device height h [m]

Figure 2 — (not to scale) Sketch of the sound source and the measurement grid in front of the noise

reducing device under test for sound reflection index measurements
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SIST EN 1793-5:2016
EN 1793-5:2016 (E)
Key
1 Noise reducing device height h [m]
2 Reference height h [m]
3 Orthogonal spacing between two subsequent microphones s [m]

Figure 3 (a) — (not to scale) Measurement grid Figure 3 (b) — (not to scale) Numbering of the

for sound reflection index measurements measurement points as seen from the sound

(source side). source.
Key
1 Source and microphone reference plane 2 Reference height h [m]
3 Loudspeaker front panel 4 Distance between the loudspeaker front panel
and the reference plane d [m]

5 Distance between the loudspeaker front 6 Distance between the measurement grid and the

panel and the measurement grid d [m] reference plane d [m]
SM M
7 Measurement grid 8 Noise reducing device height h [m]

Figure 4 — (not to scale) Placement of the sound source and measurement grid for sound reflection

index measurement for an inclined noise reducing device (side view)
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SIST EN 1793-5:2016
EN 1793-5:2016 (E)
Key
1 Reference height h [m] 2 Distance between the loudspeaker front panel and the
measurement grid d [m]
3 Loudspeaker front panel 4 Measurement grid

Figure 5 — (not to scale) Sketch of the set-up for the reference “free-field” sound measurement for

the determination of the sound reflection index
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

a0, a1, a2, a3 Coefficient for the expression of the four-term full Blackman-Harris window -

b Depth of the surface structure of the sample under test m
b 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 plane to the m
measurement grid; it is equal to d = 0,25 m

dS Horizontal distance from the front panel of the loudspeaker to the source and m

microphone reference plane; it is equal to: d = 1,50 m
d Horizontal distance from the front panel of the loudspeaker to the m
measurement grid; it is equal to: d = 1,25 m
DL Single number rating of sound reflection dB
δ Any input quantity to allow for uncertainty estimates -
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SIST EN 1793-5:2016
EN 1793-5:2016 (E)
Δf Frequency range encompassing the one-third octave frequency bands between Hz
500 Hz and 2 kHz
Δf Width of the j-the one-third octave frequency band Hz
...

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