EN 1793-4:2015

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

Diese 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 de la performance acoustique - 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

• Status: Withdrawn
• Publication Date: 17-Mar-2015
• Withdrawal Date: 30-Dec-2025
• ICS: 17.140.30 - Noise emitted by means of transport
• ICS: 93.080.30 - Road equipment and installations
• Technical Committee: CEN/TC 226 - Road equipment
• Drafting Committee: CEN/TC 226/WG 6 - Noise reducing devices
• Current Stage: 9092 - Decision on results of review/2YR ENQ - revise - Review Enquiry
• Start Date: 28-Oct-2020
• Completion Date: 31-Dec-2025
• Ref Project: SIST EN 1793-4:2015 - Road traffic noise reducing devices - Test method for determining the acoustic performance - Part 4: Intrinsic characteristics - In situ values of sound diffraction

Relations

• Replaces: CEN/TS 1793-4:2003 - Road traffic noise reducing devices - Test method for determining the acoustic performance - Part 4: Intrinsic characteristics - In situ values of sound diffraction
• Effective Date: 25-Mar-2015
• Replaced By: EN 1793-4:2025 - Road traffic noise reducing devices - Test method for determining the acoustic performance - Part 4: Intrinsic characteristics - Intrinsic sound diffraction
• Effective Date: 19-Jan-2023

Overview

EN 1793-4:2015 - "Road traffic noise reducing devices - Test method for determining the acoustic performance - Part 4: Intrinsic characteristics - In situ values of sound diffraction" is a CEN standard that specifies how to measure the sound diffraction performance of devices added to the top of noise barriers. The standard defines an in situ test method based on measuring sound pressure levels at reference points near the top edge of a barrier with and without the added device installed, and computing the acoustic benefit as the difference (correcting for any change in height).

Key topics and technical requirements

• Measured quantity: Sound pressure level difference (sound diffraction index difference) between configurations with and without the added device.
• Frequency range: Results in one‑third octave bands from 100 Hz to 5 kHz; restricted ranges are allowed if justified.
• Single‑number rating: Frequency data are reduced to a single-number rating (DL) for simplified comparison.
• Measurement geometry: Specific sound source and microphone positions are prescribed; the 2015 edition reduced source positions from six to four and microphone positions from 12 to 10 (all obligatory).
• Free‑field impulse response: A free-field impulse response is required per microphone position (removes need for geometric spreading correction).
• Height correction: Method corrects for any change in barrier height so the result represents benefit over a simple barrier of the same height.
• In situ and sample testing: Applicable to installed devices and purpose-built test samples; Annex A covers indoor (laboratory) measurements.
• Measurement uncertainty: Clause 5 and Annex B specify uncertainty considerations and calculation methods.
• Equipment and standards: Sound level meters, test signals, and other equipment must meet referenced standards (e.g., EN 61672‑1); background noise and meteorological conditions are considered.

Applications and users

This standard is intended for:

• Manufacturers of added devices (product development, interactive design, and installation manuals)
• Acoustic test laboratories and certification bodies for product qualification (outdoors or indoors)
• Road authorities, contractors, and consultants for post‑construction verification and long‑term performance checks
• Researchers studying diffraction and barrier performance

Practical uses include preliminary product qualification, verification of installed performance, comparison with design specifications, and repeated monitoring to assess durability.

Related standards

• EN 1793‑1 (sound absorption), EN 1793‑3 (normalized traffic noise spectrum), EN 1793‑6 (airborne sound insulation)
• EN 61672‑1 (sound level meters), EN ISO 354 (sound absorption measurement)
• ISO/IEC Guide 98 (GUM - uncertainty)

Keywords: EN 1793-4:2015, road traffic noise reducing devices, sound diffraction, in situ measurements, sound diffraction index, noise barrier, acoustic performance, test method.

Standards Content (Sample)

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

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.

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
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

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.
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.
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)
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
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
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 -
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 shall not exceed a value of 1,0 m (see Figure 8).
4.2.2 Reference walls
Two versions of the reference wall shall be used in the tests:
A A reflective reference wall, constructed of homogeneous panels with a smooth surface finish. The wall
shall be free of air leaks and shall have a thickness not greater than 0,20 m. The reference wall shall
have the minimum values of Sound Insulation Index measured according to EN 1793-6 specified in
Table 2, in order that the sound transmission through the reference wall is negligible.
Table 2 – Minimum values of the Sound Insulation Index of the reference wall, measured according to
EN 1793–6, tolerance ± 0,5 dB
Octave centre frequency (Hz) 125 250 500 1000 2000 4000
SI (dB)
21,0 22,0 24,0 26,0 29,0 32,0
B An absorptive reference wall, constructed as mentioned under A, lined on the source side with an
absorptive flat layer of a single porous material having the minimum values of sound absorption
coefficient measured according to EN ISO 354 specified in Table 3.
Table 3 – Minimum values of the sound absorption coefficient for the absorptive treatment of the
reference wall, measured in reverberation room, tolerance ± 0,05
Octave centre frequency (Hz) 125 250 500 1000 2000 4000
α 0,20 0,50 0,85 0,95 0,95 0,95
4.2.3 In situ tests
When applying the test method in situ on existing noise reducing devices, with the intention of obtaining
results valid over the entire frequency range specified in 4.6, the test construction shall satisfy the
requirements in 4.2.2.
If these requirements cannot be fulfilled by the existing noise reducing device, the obtained results shall only
be valid over a restricted frequency range (see 4.8.7) and for the type of noise reducing device being tested.
4.3 Positions of the sound source
Two angles of incidence, 90° and 45°, shall be used (see Figure 2 and Figure 5).
For execution of the diffraction test at a right angle to the test construction the sound source shall be placed
as follows (see Figure 1, Figure 2, Figure 4 and Figure 5):
• in the vertical plane containing the perpendicular bisector plane to the reference plane;
• horizontally: at 2 m distance from the reference plane of the test construction;
• vertically: in relation to the reference height h of the test construction,
ref
for the source position S1: centre of the source 0,50 m lower than h ;
ref
for the source position S2: centre of the source 0,15 m lower than h ;
ref
• oriented towards the microphone position M1 (see 4.4 and Figure 1 and Figure 3).
For execution of the diffraction test at an angle of 45° with the reference plane of the test construction the
sound source shall be placed as follows (see Figure 2 and Figure 5):
• in a vertical plane that makes an angle of 45° with the reference plane of the test construction, passing
through its mid-point;
• horizontally: at 2 m distance from the reference plane of the test construction;
• vertically in relation to the reference height h of the test construction,
ref
for the source position S3: centre of the source 0,50 m lower than h ;
ref
for the source position S4: centre of the source 0,15 m lower than h ;
ref
• oriented towards the microphone position M6 (see 4.4 and Figure 2 and Figure 3).
4.4 Position of the microphone(s)
For execution of the diffraction test at a right angle to the test construction the microphone(s) shall be placed
as follows (see Figure 1, Figure 2, Figure 3, Figure 4, Figure 5 and Figure 6):
• in the vertical plane containing the perpendicular bisector plane to the reference plane;
• horizontally: at 2 m distance from the reference plane of the test construction;
• vertically in relation to the reference height h of the test construction,
ref
for the microphone positions M1, M2, M3, M4 and M5:
− microphone M1: 0,50 m higher;
− microphone M2: 0,25 m higher;
− microphone M3: equal to the reference height;
− microphone M4: 0,25 m lower;
− microphone M5: 0,50 m lower;
• making an angle in the horizontal plane so as to be oriented toward the sound source.
For execution of the diffraction test at an angle of 45° with the reference plane of the test construction the
microphone(s) shall be placed as follows (see Figure 1, Figure 2, Figure 3, Figure 4 and Figure 5):
• in a vertical plane that makes an angle of 45° with the reference plane of the test construction, passing
through its mid-point;
• horizontally: at 2 m distance from the longitudinal axis of the test construction;
• vertically in relation to the reference height h of the test construction,
ref
for the microphone positions M6, M7, M8, M9 and M10:
− microphone M6: 0,50 m higher;
− microphone M7: 0,25 m higher;
− microphone M8: equal to the reference height;
− microphone M9: 0,25 m lower.
− microphone M10: 0,50 m lower.
• making an angle in the horizontal plane so as to be oriented toward the sound source.
4.5 Free-field measurements
For each set of measurements done placing the sound source according to 4.3 (90° and 45°), a “free-field”
impulse response shall be measured for each microphone position, keeping the sound source and the
microphone positions with the same geometrical configuration of the set-up and without the reference wall or
supporting barrier present (see for example Figure 7).
A whole set of measurements shall be carried out within 2 h. Otherwise a new free-field measurement shall be
carried out.
No obstacle shall be present within a distance of 3 m from the microphone(s).

Key
RP reference plane
Figure 1 ― Source and microphone positions in a vertical cross section of the test construction
without added device
Key
RP reference plane
Figure 2 ― Source and microphone positions in a top view of the test construction without added
device
Figure 3 ― Microphone positions in a vertical back view from receiver side of the test construction
without added device
Key
RP reference plane
AD added device
Figure 4 ― Source and microphone positions in a vertical cross section of the test construction with
added device
Key
RP reference plane
AD added device
Figure 5 ― Source and microphone positions in a top view of the test construction with added device
Key
AD added device
Figure 6 ― Microphone positions in a vertical back view from receiver side of the test construction
with added device
Figure 7 ― Source and microphone positions for the free-field measurement in a vertical cross
section (example given for source position S1 and microphone position M1)
Key
RP reference plane
AD added device
Figure 8 ― Maximum horizontal dimension of the added device
4.6 Measured quantity
The expression used to compute the sound diffraction index DI for all loudspeaker locations and measuring
frequencies, in one-third octave bands, is:


F h ()t w ()t df
[ ]
dk dk
∫

n 
Df
j

DI =−10lg (1)

j ∑
k=1
F h ()t w ()t df
[ ]

ik ik
∫

Df
j


where
h (t) is the component of the free-field impulse response received at the k-th measurement point
ik
(k = 1…n);
h (t) is the component of the impulse response diffracted by the top edge of the test construction
dk
and received at the k-th measurement point (k = 1…n);
w (t) is the time window (Adrienne temporal window) for the component of the free-field impulse
ik
response received at the k-th measurement point (k = 1…n);
w (t) is the time window (Adrienne temporal window) for the component of the impulse response
dk
diffracted by the top edge of the test construction and received at the k-th measurement point
(k = 1…n);
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);
is the width of the j-th one-third octave frequency band (between 100 Hz and 5 kHz);
Df
j
n = 10 is the number of measurement points (microphone positions).
The sound diffraction index shall be calculated two times:
• for the test construction without added device;
• for the test construction with added device.
For each set of measurements, at least one free-field measurement shall be carried out, as described in 4.5.
4.7 Measuring equipment
4.7.1 Components of the measuring system
The measuring equipment shall comprise: an electro-acoustic system, consisting of an electrical signal
generator, a power amplifier and a loudspeaker, one or more microphone(s) with their microphone amplifiers
and a signal analyser capable of performing transformations between the time domain and the frequency
domain.
NOTE Part of these devices can be integrated into a frequency analyser or a personal computer equipped with
specific add-on board(s).
The essential components of the measuring system are shown in Figure 9.
The complete measuring system shall meet the requirements of at least a type 1 instrument in accordance
with EN 61672-1, except for the microphone(s) which shall meet the requirements for type 2 and have a
diameter of 1/2” maximum.
The measurement procedure here described is based on ratios of the power spectra of signals extracted from
impulse responses sampled with the same equipment in the same place under the same conditions within a
short time. Also, a high accuracy in measuring sound levels is not of interest here. Strict requirements on the
absolute accuracy of the measurement chain are, therefore, not needed. Anyway, the requirement for a type 1
instrument is maintained for compatibility with other European Standards. The microphones should be
sufficiently small and lightweight in order to be fixed on a frame to constitute a microphone array without
moving.
Figure 9 ― Sketch representing the essential components of the measuring system
4.7.2 Sound source
The electro-acoustic sound source shall meet the following characteristics:
• have a single loudspeaker driver;
• be constructed without any port, e.g. to enhance low frequency response;
• be constructed without any electrically active or passive components (such as crossovers) which can
affect the frequency response of the whole system;
• have a smooth frequency response without sharp irregularities throughout the measurement frequency
range, resulting in an impulse response under free-field conditions with a length not greater than 3 ms.
NOTE As the sound diffraction index is calculated from the ratio of energetic quantities extracted from impulse
responses taken using the same loudspeaker-microphone assembly within a short time period, the characteristics of the
loudspeaker frequency response are not critical, provided a good quality loudspeaker meeting the above prescriptions is
used.
All the measurements (diffraction and free-field) shall be made with the same amplification gain.
4.7.3 Test signal
The electro-acoustic source shall receive an input electrical signal which is deterministic and exactly
repeatable. The input signal shall be set in order to avoid any nonlinearity of the loudspeaker.
The S/N ratio is improved by repeating the same test signal and synchronously averaging the microphone
response. At least 16 averages shall be kept.
This European Standard recommends the use of a MLS signal as test signal. A different test signal may be
used, e.g. sine sweep, if results can be shown to be exactly the same. This means that it shall be clearly
demonstrated that:
— the generation of the test signal is deterministic and exactly repeatable;
— impulse responses are accurately sampled (without distortion) on the whole frequency range of interest
(one-third octave bands between 100 Hz and 5 kHz);
— the test method maintains a good background noise immunity, i.e. the effective S/N ratio can be made
higher than 10 dB on the whole frequency range of interest within a short measurement time (no more
than 5 min per impulse response);
— the sample rate can be chosen high enough to allow an accurate correction of possible time shifts in the
impulse responses between the measurement in front of the sample and the free-field measurement due
to temperature changes;
— the test signal is easy-to-use, i.e. it can be conveniently generated and fed to the sound source using only
equipment which is available on the market.
4.8 Data processing
4.8.1 Calibration
The measurement procedure here described is based on ratios of the power spectra of signals extracted from
impulse responses sampled with the same equipment in the same place under the same conditions. An
absolute calibration of the measurement chain with regard to the sound pressure level is therefore not
needed. It is anyway recommended to check the correct functioning of the measurement chain from the
beginning to the end of measurements.
4.8.2 Sample rate
The frequency at which the microphone response is sampled depends on the specified upper frequency limit
of the measurement and on the anti-aliasing filter type and characteristics.
The sample rate f shall have a value greater than 43 kHz.
s
NOTE Although the signal is already unambiguously defined when the Nyquist criterion is met, higher sample rates
facilitate a better reproduction of the signal. With the prescribed sample rates errors can be detected and corrected more
easily, such as time shifts in the impulse responses between the measurements on the sample and the free-field
measurement due to temperature changes.
The sample rate shall be equal to the clock rate of the signal generator.
The cut-off frequency of the anti-aliasing filter, f , shall have a value:
co
≤
f kf
co s
(2)
where k = 1/3 for the Chebyshev filter and k = 1/4 for the Butterworth and Bessel filters.
For each measurement, the sample rate, the type and the characteristics of the anti-aliasing filter shall be
clearly stated in each test report.
4.8.3 Background noise
The effective signal-to-noi
...