SIST EN 1793-4:2015
(Main)Road traffic noise reducing devices - Test method for determining the acoustic performance - Part 4: Intrinsic characteristics - In situ values of sound diffraction
Road traffic noise reducing devices - Test method for determining the acoustic performance - Part 4: Intrinsic characteristics - In situ values of sound diffraction
This European Standard describes a test method for determining the intrinsic characteristics of sound diffraction of added devices installed on the top of traffic noise reducing devices. The test method prescribes measurements of the sound pressure level at several reference points near the top edge of a noise reducing device with and without the added device installed on its top. The effectiveness of the added device is calculated as the difference between the measured values with and without the added devices, correcting for any change in height (the method described gives the acoustic benefit over a simple barrier of the same height; however, in practice the added device can raise the height and this could provide additional screening depending on the source and receiver positions).
The test method is intended for the following applications:
- preliminary qualification, outdoors or indoors, of added devices to be installed on noise reducing devices;
- determination of sound diffraction index difference of added 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 added devices (with a repeated application of the method);
- interactive design process of new products, including the formulation of installation manuals.
The test method can be applied both in situ and on samples purposely built to be tested using the method described here.
Results are expressed as a function of frequency, in one-third octave bands between 100 Hz and 5 kHz. If it is not possible to get valid measurements results over the whole frequency range indicated, the results shall be given in the restricted frequency range and the reasons of the restriction(s) shall be clearly reported. A single-number rating is calculated from frequency data.
For indoors measurements see Annex A.
Lärmschutzvorrichtungen an Straßen - Prüfverfahren zur Bestimmung der akustischen Eigenschaften - Teil 4: Produktspezifische Merkmale - In-situ-Werte der Schallbeugung
Die Europäische Norm beschreibt ein Prüfverfahren zur Bestimmung der produktspezifischen Merkmale der Schallbeugung bei Wandaufsätzen, die auf Lärmschutzvorrichtungen für Straßen montiert werden. Das Prüfverfahren sieht Messungen des Schalldruckpegels an mehreren Bezugspunkten nahe der Oberkante der Lärmschutzvorrichtung mit und ohne montierte Wandaufsätze vor. Die Wirksamkeit des Wandaufsatzes berechnet sich aus der Differenz aus den mit und ohne Wandaufsatz gemessenen Werten unter Berücksichtigung der Änderungen der Höhe (das beschriebene Verfahren hebt den akustischen Nutzwert gegenüber einer einfachen Schutzvorrichtung derselben Höhe hervor; allerdings kann der Wandaufsatz in der Praxis die Höhe vergrößern, wodurch wiederum in Abhängigkeit von Sender- und Empfangsposition eine zusätzliche Abschirmung bereitgestellt werden kann).
Das Prüfverfahren ist für folgende Anwendungen vorgesehen:
- im Freien und in Innenräumen erfolgende Vorqualifizierung der Wandaufsätze, die auf Lärmschutzvorrichtungen montiert werden;
- Bestimmung der Schallbeugungsindex Differenz von Wandaufsätzen in der Praxis;
- Vergleich der Bemessungsspezifikationen mit den tatsächlichen Leistungsdaten nach Abschluss der Bauarbeiten;
- Überprüfung der Langzeitwirksamkeit von Wandaufsätzen (durch wiederholtes Anwenden des Verfahrens);
- interaktives Konstruktionsverfahren neuer Produkte, einschließlich der Erstellung von Montage-handbüchern.
Das Prüfverfahren kann sowohl in situ als auch an Prüfkörpern, die speziell für die Prüfung unter Verwendung des hier beschriebenen Verfahrens hergestellt wurden, angewendet werden.
Ergebnisse werden als Funktion der Frequenz in Terzbändern zwischen 100 Hz und 5 kHz angegeben. Ist es nicht möglich, gültige Messergebnisse über den gesamten Frequenzbereich zu gewinnen, müssen die Ergebnisse für den eingeschränkten Frequenzbereich zusammen mit den Gründen für die Einschränkung(en) klar angegeben werden. Aus den Frequenzdaten wird eine Einzahl Angabe berechnet.
Hinsichtlich Messungen in Innenräumen siehe Anhang A.
Dispositifs de réduction du bruit du trafic routier - Méthode d'essai pour la détermination des performances acoustiques - Partie 4: Caractéristiques intrinsèques - Valeurs in-situ de la diffraction acoustique
La présente Norme européenne décrit une méthode d'essai permettant de déterminer les caractéristiques intrinsèques de la diffraction acoustique des dispositifs additionnels installés au sommet des dispositifs de réduction du bruit. La méthode d'essai prescrit des mesures du niveau de pression acoustique en différents points de référence situés près du bord supérieur d'un dispositif de réduction du bruit, avec et sans dispositif additionnel installé au sommet. L'efficacité du dispositif additionnel est calculée comme étant la différence entre les valeurs mesurées avec et sans dispositifs additionnels, avec une correction pour tout changement de hauteur (la méthode décrite indique l'avantage acoustique par rapport à une barrière simple de même hauteur ; cependant, dans la pratique, le dispositif additionnel peut augmenter cette hauteur et fournir une atténuation supplémentaire en fonction des positions respectives de la source et du récepteur).
La méthode d'essai est destinée aux applications suivantes :
- la qualification préliminaire, à l'extérieur ou l'intérieur à de bâtiments, des dispositifs additionnels à installer sur les dispositifs de réduction du bruit ;
- la détermination de la différence d'indice de diffraction acoustique des dispositifs additionnels actuellement utilisés ;
- la comparaison des spécifications de conception avec des données de performance réelles de l'ouvrage achevé ;
- la vérification des performances à long terme de dispositifs additionnels (par l'application répétée de la méthode) ;
- le processus interactif de conception de nouveaux produits, y compris l'élaboration de manuels d'installation.
La méthode d'essai peut être appliquée à la fois in situ et sur des échantillons construits spécifiquement pour être soumis à essai selon la méthode décrite dans le présent document.
Les résultats sont exprimés en fonction de la fréquence, par bandes de tiers d'octave pour la plage comprise entre 100 Hz et 5 kHz. S'il est impossible d'obtenir des résultats de mesures valides sur toute la plage de fréquences indiquée, convient de donner les résultats pour la plage de fréquence réduite et de consigner clairement les raisons de la ou des restriction(s). Un indice unique d'évaluation est calculé à partir des données de fréquence.
Voir l’Annexe A pour les mesures en intérieur.
Protihrupne ovire za cestni promet - Preskusna metoda za ugotavljanje akustičnih lastnosti - 4. del: Bistvene lastnosti - Terenske vrednosti difrakcije zvoka
Ta evropski standard opisuje preskusno metodo za ugotavljanje bistvenih lastnosti difrakcije zvoka dodanih ovir, nameščenih na protihrupne ovire za cestni promet. Preskusna metoda opisuje meritve ravni zvočnega tlaka na različnih referenčnih točkah blizu zgornjega roba protihrupne ovire z dodano oviro ali brez nje. Učinkovitost dodane ovire se izračuna kot razlika med izmerjenimi vrednostmi z dodanimi ovirami ali brez njih, s korekcijo sprememb višine (opisana metoda podaja akustične koristi preproste ovire z isto višino, vendar lahko v praksi dodana ovira presega višino, kar lahko omogoča dodatno zaslonitev glede na položaj vira in sprejemnika).
Preskusna metoda je namenjena:
– predhodni kvalifikaciji, v zunanjih in notranjih okoljih, dodanih ovir, ki se namestijo na protihrupne ovire; – ugotavljanju indeksa difrakcije zvoka dodanih ovir med dejansko uporabo; – primerjavi specifikacij zasnove s podatki o dejanskih lastnostih po koncu gradnje; – preverjanje dolgoročnih lastnosti dodanih ovir (z večkratno izvedbo metode); – interaktivnemu postopku zasnove novih izdelkov, vključno s pripravo navodil za namestitev.
Preskusna metoda se lahko uporablja na kraju samem ali na vzorcih, zgrajenih posebej za preskus z opisano metodo.
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. Iz podatkov o pogostosti se izračuna enoštevilčna ocena.
Za meritve v notranjih okoljih glej dodatek A.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 1793-4:2015
01-maj-2015
1DGRPHãþD
SIST-TS CEN/TS 1793-4:2004
3URWLKUXSQHRYLUH]DFHVWQLSURPHW3UHVNXVQDPHWRGD]DXJRWDYOMDQMHDNXVWLþQLK
ODVWQRVWLGHO %LVWYHQHODVWQRVWL7HUHQVNHYUHGQRVWLGLIUDNFLMH]YRND
Road traffic noise reducing devices - Test method for determining the acoustic
performance - Part 4: Intrinsic characteristics - In situ values of sound diffraction
Lärmschutzvorrichtungen an Straßen - Prüfverfahren zur Bestimmung der akustischen
Eigenschaften - Teil 4: Produktspezifische Merkmale - In-situ-Werte der Schallbeugung
Dispositifs de réduction du bruit du trafic routier - Méthode d'essai pour la détermination
des performances acoustiques - Partie 4: Caractéristiques intrinsèques - Valeurs in-situ
de la diffraction acoustique
Ta slovenski standard je istoveten z: EN 1793-4:2015
ICS:
17.140.01 $NXVWLþQDPHUMHQMDLQ Acoustic measurements and
EODåHQMHKUXSDQDVSORãQR noise abatement in general
93.080.30 Cestna oprema in pomožne Road equipment and
naprave installations
SIST EN 1793-4:2015 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN 1793-4:2015
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SIST EN 1793-4:2015
EUROPEAN STANDARD
EN 1793-4
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2015
ICS 17.140.30; 93.080.30 Supersedes CEN/TS 1793-4:2003
English Version
Road traffic noise reducing devices - Test method for
determining the acoustic performance - Part 4: Intrinsic
characteristics - In situ values of sound diffraction
Dispositifs de réduction du bruit du trafic routier - Méthode Lärmschutzvorrichtungen an Straßen - Prüfverfahren zur
d'essai pour la détermination des performances Bestimmung der akustischen Eigenschaften - Teil 4:
acoustiques - Partie 4: Caractéristiques intrinsèques - Produktspezifische Merkmale - In-situ-Werte der
Valeurs in-situ de la diffraction acoustique Schallbeugung
This European Standard was approved by CEN on 13 December 2014.
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
© 2015 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 1793-4:2015 E
worldwide for CEN national Members.
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SIST EN 1793-4:2015
EN 1793-4:2015 (E)
Contents Page
Foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions and symbols . 7
3.1 Terms and definitions . 7
3.2 Symbols . 8
4 Sound diffraction index difference measurements . 10
4.1 General principle . 10
4.2 Dimensions and specifications . 10
4.2.1 Added devices . 10
4.2.2 Reference walls . 10
4.2.3 In situ tests . 11
4.3 Positions of the sound source . 11
4.4 Position of the microphone(s) . 12
4.5 Free-field measurements . 13
4.6 Measured quantity . 17
4.7 Measuring equipment . 18
4.7.1 Components of the measuring system . 18
4.7.2 Sound source . 19
4.7.3 Test signal . 20
4.8 Data processing . 20
4.8.1 Calibration . 20
4.8.2 Sample rate. 20
4.8.3 Background noise . 21
4.8.4 Measurement points . 21
4.8.5 Adrienne temporal window . 21
4.8.6 Placement of the Adrienne temporal window . 22
4.8.7 Low frequency limit and sample size . 23
4.9 Positioning of the measuring equipment . 24
4.9.1 Selection of the measurement positions . 24
4.9.2 Reflecting objects . 24
4.9.3 Safety considerations . 25
4.10 Sound diffraction index difference . 25
4.11 Single-number rating of sound diffraction index difference DL . 25
ΔDI
4.12 Sample surface and meteorological conditions . 26
4.12.1 Condition of the sample surface . 26
4.12.2 Wind . 26
4.12.3 Air temperature . 26
5 Measurement uncertainty . 26
6 Measuring procedure . 26
6.1 General . 26
6.2 Test report . 27
Annex A (informative) Indoor measurements for product qualification . 29
A.1 General . 29
A.2 Parasitic reflections . 29
A.3 Reverberation time of the room . 29
Annex B (informative) Measurement uncertainty. 30
2
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EN 1793-4:2015 (E)
B.1 General . 30
B.2 Expression for the calculation of sound diffraction index. 30
B.3 Contributions to measurement uncertainty. 31
B.4 Expanded uncertainty of measurement . 32
B.5 Measurement uncertainty based upon reproducibility data . 32
Bibliography . 33
3
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SIST EN 1793-4:2015
EN 1793-4:2015 (E)
Foreword
This document (EN 1793-4:2015) 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 September 2015 and conflicting national standards shall be withdrawn
at the latest by September 2015.
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.
This document supersedes CEN/TS 1793-4:2003.
The major changes compared to the previous published version are:
− the airborne sound insulation characteristics of the reference wall are specified in terms of the minimum
values of the Sound Insulation Index, measured according to EN 1793-6, it needs to have;
− the sound absorbing characteristics of the reference wall are specified in terms of the minimum values of
the sound absorption coefficient, measured according to EN ISO 354, it needs to have when lined on the
source side with an absorptive flat layer of a single porous material;
− the sound source positions have been reduced from six to four and are now all obligatory;
− the microphone positions have been reduced from 12 to 10 and are now all obligatory;
− a “free-field” impulse response to be measured for each microphone position and therefore a geometrical
spreading correction factor is no more needed in Formula (1);
− consideration of the measurement uncertainty has been added (see Clause 5 and Annex B);
− the summary of the test procedure (Clause 6) has been updated to reflect the changes compared to the
previous published version.
This document 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 1793-3, Road traffic noise reducing devices ― Test method for determining the acoustic performance ―
Part 3: Normalized traffic noise spectrum
CEN/TS 1793-5, Road traffic noise reducing devices ― Test method for determining the acoustic performance
― Part 5: Intrinsic characteristics ― In situ values of sound reflection and airborne sound insulation.
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
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.
4
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SIST EN 1793-4:2015
EN 1793-4:2015 (E)
Introduction
Part of the market of road traffic noise reducing devices is constituted of products to be added on the top of
noise reducing devices and intended to contribute to sound attenuation acting primarily on the diffracted
sound field. These products will be called added devices. This European Standard has been developed to
specify a test method for determining the acoustic performance of added devices.
The test method can be applied in situ, i.e. where the traffic noise reducing devices and the added devices are
installed. The method can be applied without damaging the traffic noise reducing devices or the added
devices.
The method can be used to qualify products before the installation along roads as well as to verify the
compliance of installed added devices to design specifications. Repeated application of the method can be
used to verify the long term performance of added devices.
This method could be used to qualify added devices for other applications, e.g. to be installed along railways
or nearby industrial sites. In this case, special care needs to be taken into account in considering the location
of the noise sources and the single-number ratings should be calculated using an appropriate spectrum.
No other national or international standard exists about the subject of this European Standard.
5
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SIST EN 1793-4:2015
EN 1793-4:2015 (E)
1 Scope
This European Standard describes a test method for determining the intrinsic characteristics of sound
diffraction of added devices installed on the top of traffic noise reducing devices. The test method prescribes
measurements of the sound pressure level at several reference points near the top edge of a noise reducing
device with and without the added device installed on its top. The effectiveness of the added device is
calculated as the difference between the measured values with and without the added devices, correcting for
any change in height (the method described gives the acoustic benefit over a simple barrier of the same
height; however, in practice the added device can raise the height and this could provide additional screening
depending on the source and receiver positions).
The test method is intended for the following applications:
• preliminary qualification, outdoors or indoors, of added devices to be installed on noise reducing devices;
• determination of sound diffraction index difference of added 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 added devices (with a repeated application of the method);
• interactive design process of new products, including the formulation of installation manuals.
The test method can be applied both in situ and on samples purposely built to be tested using the method
described here.
Results are expressed as a function of frequency, in one-third octave bands between 100 Hz and 5 kHz. If it is
not possible to get valid measurements results over the whole frequency range indicated, the results shall be
given in the restricted frequency range and the reasons of the restriction(s) shall be clearly reported. A single-
number rating is calculated from frequency data.
For indoors measurements see Annex A.
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 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
EN 61672-1, Electroacoustics ― Sound level meters ― Part 1: Specifications
EN ISO 354, Acoustics ― Measurement of sound absorption in a reverberation room (ISO 354)
ISO/IEC Guide 98, Guide to the expression of uncertainty in measurement (GUM)
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EN 1793-4:2015 (E)
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
3.1.1
structural elements
those elements whose primary function is to support or hold in place acoustic elements
3.1.2
acoustical elements
those elements whose primary function is to provide the acoustic performance of the device
3.1.3
noise barrier
noise reducing device which obstructs the direct transmission of airborne sound emanating from road traffic
3.1.4
added device
acoustic element added on the top of a noise reducing device and intended to contribute to sound attenuation
acting primarily on the diffracted sound field
3.1.5
roadside exposure
use of the product as a noise reducing device installed alongside roads
3.1.6
sound diffraction index
result of a sound diffraction test whose components are described by the formula in 4.6
Note 1 to entry: The symbol for the sound diffraction index includes information on the setup used during the test:
DI refers to measurements on a reflective reference wall. DI refers to measurements on an absorptive reference
x,refl x,abs
wall. DI refers to in situ measurements; where x is “0” when the added device is not on the top of the test construction
x,situ
and “ad” when the added device is on the top of the test construction (see 3.2).
3.1.7
sound diffraction index difference
difference between the results of sound diffraction tests on the same reference wall with and without an added
device on the top, described by the formulae in 4.10
3.1.8
test construction
construction on which the added device is placed
Note 1 to entry: For in situ measurements the test construction is an installed noise reducing device; for qualification
tests it is a reference wall (see 4.2).
3.1.9
reference plane of the test construction
vertical plane passing through the midpoint of the top edge of the construction (reference wall or installed
noise reducing device) on which the added device has to be placed (see Figure 1, Figure 2, Figure 4, Figure 5
and Figure 8)
3.1.10
reference height of the test construction without the added device, h
ref,0
height of the highest point of the test construction in relation to the surrounding ground surface
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EN 1793-4:2015 (E)
Note 1 to entry: This highest point is not necessarily lying in the plane of longitudinal symmetry of the reference test
construction, if this symmetry exists (Figure 1).
3.1.11
reference height of the test construction with the added device on the top, h
ref,add
height of the highest point of the added device installed on the test construction in relation to the surrounding
ground surface
Note 1 to entry: This highest point is not necessarily lying in the plane of longitudinal symmetry of the reference test
construction, if this symmetry exists (Figure 4).
3.1.12
free-field measurement for sound diffraction index measurements
measurement carried out placing the loudspeaker and the microphone as specified in 4.3, 4.4 and 4.5 without
any obstacle, including the test construction with or without added device, between them (see for example
Figure 7)
3.1.13
Adrienne temporal window
composite temporal window described in 4.8.5
3.1.14
background noise
noise coming from sources other than the source emitting the test signal
3.1.15
signal-to-noise ratio, S/N
difference in decibels between the level of the test signal and the level of the background noise at the moment
of detection of the useful event (within the Adrienne temporal window)
3.1.16
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
3.2 Symbols
For the purposes of this document, the following symbols and abbreviations apply.
Table 1 – Symbols and abbreviations
Symbol or
Designation Unit
abbreviation
α Sound absorption coefficient measured according to EN ISO 354 -
DI Sound diffraction index in the j-th one-third octave frequency band dB
j
DI Sound diffraction index for the reflective reference wall without the added dB
0,refl
device
DI Sound diffraction index for the reflective reference wall with the added device dB
ad,refl
DI Sound diffraction index for the absorptive reference wall without the added dB
0,abs
device
DI Sound diffraction index for the absorptive reference wall with the added device dB
ad,abs
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DI Sound diffraction index for the in situ test construction without the added dB
0,situ
device
DI Sound diffraction index for the in situ test construction with the added device dB
ad,situ
ΔDI Sound diffraction index difference for the test sample on the reflective dB
refl
reference wall
ΔDI Sound diffraction index difference for the test sample on the absorbing dB
abs
reference wall
ΔDI Sound diffraction index difference for the test sample on an situ test dB
situ
construction
DL Single-number rating of sound diffraction index difference for the test sample dB
ΔDI,refl
on the reflective reference wall
DL Single-number rating of sound diffraction index difference for the test sample dB
ΔDI,abs
on the absorbing reference wall
DL Single-number rating of sound diffraction index difference for the test sample dB
ΔDI,situ
on the in situ test construction
δ Any input quantity to allow for uncertainty estimates -
i
Δf Width of the j-th one-third octave frequency band Hz
i
f Frequency Hz
F Symbol of the Fourier transform -
f Low frequency limit of sound diffraction index measurements Hz
min
f Sample rate Hz
s
f Cut-off frequency of the anti-aliasing filter Hz
co
h Noise barrier height m
B
h Reference height of the test construction m
ref
h Reference height of the test construction without the added device m
ref,0
h Reference height of the test construction with the added device m
ref,ad
h (t) Incident reference component of the free-field impulse response dB
i
h (t) Diffracted component of the impulse response at the k-th measurement point dB
d,k
j Index of the j-th one-third octave frequency band (between 100 Hz and 5 kHz) -
k Coverage factor -
k Constant used for the anti-aliasing filter -
f
L Minimum length of the reference wall m
b
L Minimum length of the added device under test m
d
n Number of measurement points -
SI Sound Insulation Index measured according to EN 1793–6 dB
t Time s or
ms
T Length of the Blackman-Harris trailing edge of the Adrienne temporal window ms
W,BH
T Total length of the Adrienne temporal window ms
W,ADR
u Standard uncertainty -
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U Expanded uncertainty -
w (t) Time window (Adrienne temporal window) for the component of the free-field -
ik
impulse response received at the k-th measurement point
w (t) Time window (Adrienne temporal window) for the component of the impulse -
t,k
response diffracted by the top edge of the test construction and received at the
k-th measurement point
4 Sound diffraction index difference measurements
4.1 General principle
The sound source emits a transient sound wave that travels toward the noise reducing device under test and
is partly reflected, partly transmitted and partly diffracted by it. The microphone placed on the other side of the
noise reducing device receives both the transmitted sound pressure wave travelling from the sound source
through the noise reducing device and the sound pressure wave diffracted by the top edge of the noise
reducing device under test (for the test to be meaningful the diffraction from the vertical edges of the test
construction shall be sufficiently delayed in order to be outside the Adrienne temporal window). If the
measurement is repeated without the added device and the test construction between the loudspeaker and
the microphone, the direct free-field wave can be acquired. The power spectra of the direct and the top-edge
diffracted components, corrected to take into account the path length difference of the two components, give
the basis for calculating the sound diffraction index.
The final sound diffraction index shall be a weighted average of the diffraction indices measured at different
points (see Figure 1, Figure 2, Figure 3, Figure 4, Figure 5 and Figure 6).
When the test method is applied in situ, the measurement procedure and sound diffraction index calculation
shall be carried out two times, with and without the added device placed on the test construction.
When the test method is applied on samples purposely built to be tested according to the present standard,
the added device shall be subsequently placed on the top of two reference walls (reflective and absorptive), or
of the same reference wall in two different configurations, (see 4.2) and the measurement procedure and
sound diffraction index calculation shall be carried out for both walls, with and without the added device on the
top.
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 Dimensions and specifications
4.2.1 Added devices
The added device shall have a minimum length L of 10 m. The reference wall shall have a minimum length L
d b
of 10 m and a minimum height of 4 m. The reference wall shall be vertical, flat and fixed firmly and without any
air gaps on a supporting construction (foundation, floor etc.). The top surface of the supporting construction
shall be level with the surrounding ground surface.
The maximum size of the added device measured perpendicularly from the reference plane either in the
direction of the source or in the direction of the microphones
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