Acoustics -- Software for the calculation of sound outdoors

This document facilitates a standardized interpretation and a verifiably consistent software implementation of the sound propagation part of the calculation method CNOSSOS-EU:2015 according to ISO 17534-1. Other parts of CNOSSOS-EU:2015, such as the source models or the calculation method for aircraft noise, are beyond the scope of this document. This document provides an agreed interpretation of ambiguous aspects of the sound propagation part of CNOSSOS-EU:2015, a set of illustrative test cases along with reference solutions, and an example of a template form for the declaration of conformity for software manufacturers.

Acoustique -- Logiciels de prévision de bruit dans l'environnement

General Information

Status
Published
Publication Date
15-Nov-2020
Technical Committee
Drafting Committee
Current Stage
5060 - Close of voting Proof returned by Secretariat
Start Date
16-Oct-2020
Completion Date
16-Oct-2020
Ref Project

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TECHNICAL ISO/TR
REPORT 17534-4
First edition
2020-11
Acoustics — Software for the
calculation of sound outdoors —
Part 4:
Recommendations for a quality
assured implementation of the
COMMISSION DIRECTIVE (EU)
2015/996 in software according to
ISO 17534-1
Acoustique — Logiciels de prévision de bruit dans l'environnement —
Partie 4: Recommandations pour l'assurance qualité de la mise
en œuvre de la DIRECTIVE (UE) 2015/996 de la COMMISSION
EUROPÉENNE dans les logiciels selon l'ISO 17534-1
Reference number
ISO/TR 17534-4:2020(E)
ISO 2020
---------------------- Page: 1 ----------------------
ISO/TR 17534-4:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/TR 17534-4:2020(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Identification of the official documentation ............................................................................................................................ 1

5 Uniform and agreed interpretation of ambiguities.......................................................................................................... 2

5.1 General ........................................................................................................................................................................................................... 2

5.2 Sloping objects ........................................................................................................................................................................................ 2

5.3 Equivalent heights ................................................................................................................................................................................ 2

5.4 Alternative statistical approach ............................................................................................................................................... 3

5.5 Octave band centre frequency f .............................................................................................................................................

m 3

5.6 Ground factor of the source area, G ......................................................................................................................................

S 3

5.7 Distances in Figure 2.5.b of CNOSSOS-EU: 2015 ......................................................................................................... 3

5.8 Equivalent heights in Equation (2.5.20) of CNOSSOS-EU: 2015 .................................................................... 3

5.9 Rayleigh’s Criterion ............................................................................................................................................................................. 4

5.10 Parameter e .................................................................................................................................................................................................4

5.11 Diffraction under favourable conditions .......................................................................................................................... 4

5.12 Error in Figure 2.5.f and Equation (2.5.29) of CNOSSOS-EU: 2015 ............................................................ 5

5.13 Lateral diffraction ................................................................................................................................................................................. 5

5.14 Reflection on nearly vertical objects .................................................................................................................................... 6

5.15 Retrodiffraction ...................................................................................................................................................................................... 6

6 Test cases ...................................................................................................................................................................................................................... 7

6.1 General ........................................................................................................................................................................................................... 7

6.2 Test cases with intermediate and final results ............................................................................................................ 8

6.2.1 TC01-TC03 — Flat ground with homogeneous acoustic properties ................................... 8

6.2.2 TC01 — Reflecting ground (G = 0).................................................................................................................... 8

6.2.3 TC02 — Mixed ground (G = 0,5) ......................................................................................................................... 9

6.2.4 TC03 — Porous ground (G = 1) ........................................................................................................................10

6.2.5 TC04 — Flat ground with spatially varying acoustic properties ........................................10

6.2.6 TC05 — Ground with spatially varying heights and acoustic properties ....................12

6.2.7 TC06 — Reduced receiver height to include diffraction in some frequency

bands .......................................................................................................................................................................................14

6.2.8 TC07 — Flat ground with spatially varying acoustic properties and long

barrier ....................................................................................................................................................................................17

6.2.9 TC08 — Flat ground with spatially varying acoustic properties and short

barrier ....................................................................................................................................................................................20

6.2.10 TC09 — Ground with spatially varying heights and and acoustic

properties and short barrier ..............................................................................................................................24

6.2.11 TC10 — Flat ground with homogeneous acoustic properties and cubic

building — Receiver at low height ................................................................................................................30

6.2.12 TC11 — Flat ground with homogeneous acoustic properties and cubic

object – receiver at large height .......................................................................................................................33

6.2.13 TC12 — Flat ground with homogeneous acoustic properties and

polygonal object — Receiver at low height ............................................................................................38

6.2.14 TC13 — Ground with spatially varying heights and acoustic properties

and polygonal object ........................................................................................................................................... .......42

6.2.15 TC14 — Flat ground with homogeneous acoustic properties and

polygonal object — Receiver at large height ........................................................................................47

6.2.16 TC15 — Flat ground with homogeneous acoustic properties and four buildings 53

6.2.17 TC16 — Reflecting barrier on ground with spatially varying heights and

acoustic properties .....................................................................................................................................................57

© ISO 2020 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/TR 17534-4:2020(E)
6.2.18 TC17 — Reflecting barrier on ground with spatially varying heights and

acoustic properties — Reduced receiver height................................................................................62

6.2.19 TC18 — Screening and reflecting barrier on ground with spatially varying

heights and acoustic properties .................. .....................................................................................................66

6.2.20 TC19 — Complex object and 2 barriers on ground with spatially varying

heights and acoustic properties .................. .....................................................................................................70

6.2.21 TC20 — Ground with spatially varying heights and acoustic properties ....................76

6.2.22 TC21 — Building on ground with spatially varying heights and acoustic

properties............................................................................................................................................................................78

6.2.23 TC22 — Building with receiver backside on ground with spatially varying

heights and acoustic properties .................. .....................................................................................................84

6.2.24 TC23 — Two buildings behind an earth-berm on flat ground with

homogeneous acoustic properties ................................................................................................................89

6.2.25 TC24 — Two buildings behind an earth-berm on flat ground with

homogeneous acoustic properties – receiver position modified ........................................94

6.2.26 TC25 — Replacement of the earth-berm by a barrier ...............................................................100

6.2.27 TC26 — Road source with influence of retrodiffraction .........................................................106

6.2.28 TC27 — Source located in flat cut with retro-diffraction .......................................................109

6.2.29 TC28 — Propagation over a large distance with many buildings between

source and receiver .................................................................................................................................................114

6.3 Summary of the final results .................................................................................................................................................121

7 Example of a template form for the declaration of conformity ....................................................................122

Bibliography .........................................................................................................................................................................................................................124

iv © ISO 2020 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/TR 17534-4:2020(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

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

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.

A list of all parts in the ISO 17534 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
© ISO 2020 – All rights reserved v
---------------------- Page: 5 ----------------------
ISO/TR 17534-4:2020(E)
Introduction

The structure of the ISO 17534 series is shown in Figure 1. ISO 17534-1 describes the general approach

of the ISO 17534 series, aiming to facilitate a standardized interpretation and a verifiably consistent

software implementation of outdoor sound calculation methods. ISO/TR 17534-2 contains general

recommendations for test cases and for a quality assurance interface. Further parts of the ISO 17534

series each address a specific outdoor sound calculation method for which they provide an agreed

interpretation of ambiguous aspects, a set of illustrative test cases along with reference solutions, and

an example of a template form for the declaration of conformity for software developers.

This document addresses the calculation method laid down in the COMMISSION DIRECTIVE (EU)

2015/996, hereafter referred to as CNOSSOS -EU: 2015.

The European Commission developed Common NOise aSSessment methOdS (CNOSSOS-EU) for road,

railway, aircraft and industrial noise for the purpose of strategic noise mapping. CNOSSOS-EU aims at

improving the consistency and comparability of noise assessment results across the EU Member States

which are performed on the basis of the data becoming available through the consecutive rounds of

strategic noise mapping in Europe.
Figure 1 — Structure of the ISO 17534 series
vi © ISO 2020 – All rights reserved
---------------------- Page: 6 ----------------------
TECHNICAL REPORT ISO/TR 17534-4:2020(E)
Acoustics — Software for the calculation of sound
outdoors —
Part 4:
Recommendations for a quality assured implementation
of the COMMISSION DIRECTIVE (EU) 2015/996 in software
according to ISO 17534-1
1 Scope

This document facilitates a standardized interpretation and a verifiably consistent software

implementation of the sound propagation part of the calculation method CNOSSOS -EU: 2015 according to

ISO 17534-1. Other parts of CNOSSOS -EU: 2015, such as the source models or the calculation method for

aircraft noise, are beyond the scope of this document. This document provides an agreed interpretation

of ambiguous aspects of the sound propagation part of CNOSSOS -EU: 2015, a set of illustrative test cases

along with reference solutions, and an example of a template form for the declaration of conformity for

software manufacturers.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 17534-1, Acoustics — Software for the calculation of sound outdoors — Part 1: Quality requirements

and quality assurance

ISO/TR 17534-2, Acoustics — Software for the calculation of sound outdoors — Part 2: General

recommendations for test cases and quality assurance interface

COMMISSION DIRECTIVE (EU) 2015/996 of 19 May 2015 establishing common noise assessment

methods according to Directive 2002/49/EC of the European Parliament and of the Council, Official

Journal of the European Union, L 168/1
3 Terms and definitions

For the purposes of this document, the terms and definitions given in CNOSSOS -EU: 2015, ISO 17534-1,

and ISO/TR 17534-2 apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Identification of the official documentation

COMMISSION DIRECTIVE (EU) 2015/996 of 19 May 2015 establishing common noise assessment

methods according to Directive 2002/49/EC of the European Parliament and of the Council, Official

Journal of the European Union, L 168/1, herein referred to as CNOSSOS -EU: 2015.
© ISO 2020 – All rights reserved 1
---------------------- Page: 7 ----------------------
ISO/TR 17534-4:2020(E)

In its Chapter 2.5, “Calculation of noise propagation for road, railway, industrial sources”, CNOSSOS -EU:

2015 describes a method for calculating the attenuation of sound during propagation outdoors in order

to predict the levels of environmental noise at a distance from a variety of sources.

5 Uniform and agreed interpretation of ambiguities
5.1 General

The propagation of sound outdoors in CNOSSOS -EU: 2015 is calculated with a ray-based energetic model.

Attenuations are calculated in eight octave bands, and separately for two idealized meteorological

conditions labelled homogeneous and favourable. Finally, the A-weighted exposure level at a receiver

position is given as the weighted energetic sum over all sources, paths, meteorological conditions, and

octave bands.

Some aspects of the sound propagation model of CNOSSOS -EU: 2015 are not described in sufficient detail

to be unambiguous; in other aspects, in some part the official documentation is misleading. For each of

these problematic topics, an agreed interpretation is given in 5.2 to 5.15 to allow for a standardized

u nder s t a nd i n g of C NOS S OS -E U: 2015 .

The abbreviations are not explained when they are identical to those described in CNOSSOS -EU: 2015.

Symbols are not defined when they are identical to those applied in CNOSSOS -EU: 2015.

5.2 Sloping objects

Topic: CNOSSOS -EU: 2015 states in subclause 2.5.1 that “obstacles sloping, when modelled, more than

15° in relation to the vertical are out of the scope of this calculation method”. This restriction does not

constitute a general restriction of the method. Rather, it applies only to reflectors: obstacles sloping

more than 15° in relation to the vertical are not considered as reflectors.
Agreed interpretation:

Objects sloping more than 15° in relation to the vertical are not considered as reflectors, but are taken

into account in all other aspects of propagation such as ground effects and diffraction.

5.3 Equivalent heights

Topic: CNOSSOS -EU: 2015 states in subclause 2.5.3, under the headline "Significant heights above the

ground", that “If the equivalent height of a point becomes negative, i.e. if the point is located below

the mean ground plane, a null height is retained, and the equivalent point is then identical with its

possible image.” For points located below the mean ground plane, the equivalent height is set to zero in

the calculation of A . For the calculation of path length differences, it is irrelevant whether points

ground

lie above or below a mean ground plane, no points are shifted. For the calculation of Δ and

ground(S,O)

Δ special care has to be taken in the case that one of the respective end points lies below the

ground(O,R)
mean ground plane.
Agreed interpretation:

The first major step in the algorithm is to decide whether A or A must be calculated. The step

ground dif

is based on real coordinates, not equivalent heights. If a point lies below the mean ground plane, its

equivalent height is set to zero in the calculation of A . Equations (2.5.31) and (2.5.32) of CNOSSOS

ground

-EU: 2015 apply only in the most common case that both S and R lay above the mean ground plane. If

either S or R lies below the mean ground plane, the following simplified Equations apply:

Δ = A (CNOSSOS -EU: 2015, 2.5.31)
ground(S,O) ground(S,O)
Δ = A (CNOSSOS -EU: 2015, 2.5.32)
ground(O,R) ground(O,R)
2 © ISO 2020 – All rights reserved
---------------------- Page: 8 ----------------------
ISO/TR 17534-4:2020(E)

For the calculation of path length differences, the original coordinates are used and no points are

shifted, i.e. in the calculation of Δ the original heights of S and R are used.
dif(S,R)
5.4 Alternative statistical approach

Topic: CNOSSOS -EU: 2015 mentions in subclause 2.5.5, under the headline "Statistical approach inside

urban areas for a path (S, R)", a statistical approach for calculations inside urban areas beyond the

first line of buildings. This approach is not described in sufficient detail to be subjected to the quality

assurance methodology of ISO 17534-1.
Agreed interpretation:

A statistical approach is not appropriate in the calculation of sound propagation beyond the first line of

buildings.
5.5 Octave band centre frequency f

Topic: CNOSSOS -EU: 2015 is somewhat ambiguous about whether nominal centre frequencies or exact

centre frequencies should be used in the calculation of the atmospheric attenuation coefficient α .

atm
Agreed interpretation:

In the calculation of the atmospheric attenuation coefficient α , ISO 9613-1 is followed, and exact centre

atm

frequencies are used. In all other calculations, the nominal centre frequency, denoted f , are used.

The tabulated values in ISO 9613-1 are based on the pressure at sea level.
5.6 Ground factor of the source area, G

Topic : C NOS S OS -E U: 2015 i nt r o duc e s G in subclause 2.5.6 as the ground factor G of the source area. For

industrial sources, it is left open how exactly G is to be calculated.
Agreed interpretation:

For industrial point sources, G is calculated as the average of the ground factor G over a distance of 1 m

beginning at the vertical projection point below the source and proceeding along the direction source-

receiver.
5.7 Distances in Figure 2.5.b of CNOSSOS -EU: 2015

Topic: In CNOSSOS -EU: 2015, it is unclear whether the distances d displayed in Figure 2.5.b are

3D-distances along the ground or 2D-projection onto a horizontal plane.
Agreed interpretation:

Figure 2.5.b displays a 2D-projection onto the horizontal plane. The distances d used in the calculation

of G are measured in this horizontal plane.
path
5.8 Equivalent heights in Equation (2.5.20) of CNOSSOS -EU: 2015

Topic: CNOSSOS -EU: 2015 explains that modified equivalent heights should be used in the calculation of

A . But it is unclear whether these modified equivalent heights or unmodified equivalent heights

ground,F

should be used in the calculation of A according to Equation (2.5.20) of CNOSSOS -EU: 2015.

ground,F,min
Agreed interpretation:

Unmodified equivalent heights are used in the calculation of A according to Equation (2.5.20)

ground,F,min
of C NOS S OS -E U: 2015 .
© ISO 2020 – All rights reserved 3
---------------------- Page: 9 ----------------------
ISO/TR 17534-4:2020(E)
5.9 Rayleigh’s Criterion

Topic: CNOSSOS -EU: 2015 states that no diffraction should be calculated if the ray path passes "high

enough" over the diffraction edge. In this context, CNOSSOS -EU: 2015 refers to Rayleigh’s Criterion

without providing details or formulae. The circumstances under which diffraction is calculated should

be defined unambiguously.
Agreed interpretation:

In the unique vertical plane containing source and receiver, the line of sight from source to receiver

is defined, under homogeneous conditions, as the straight line connecting source and receiver. Under

favourable conditions, the line of sight is defined as the arc of radius Γ, given by Equation (2.5.24) of

CNOSSOS -EU: 2015, connecting source and receiver.

The decision whether diffraction must be calculated is made separately for homogeneous and favourable

conditions respectively. If the line of sight is blocked, diffraction is always calculated. If the line of sight

from source to receiver is unobstructed, Rayleigh’s Criterion is employed as follows: first, that point

D of the terrain profile including obstacles is identified, which gives the largest δ , i.e. the δ with the

D D

smallest absolute value. Then δ * is calculated as the path length difference from S’ to R’ via D, where S’

and R’ are the respective images of source and receiver constructed with the appropriate mean ground

planes containing source or receiver. Diffraction is calculated only if δ > -λ/20 and δ > λ/4 - δ *

D D D

(Rayleigh’s Criterion), where λ is the wavelength at the nominal centre frequency and calculated with a

speed of sound of 340 m/s.
5.10 Parameter e

Topic: CNOSSOS -EU: 2015 introduces the parameter e as the total distance along the path from the first

to the last diffraction edge according to the "rubber band method". It is unclear how the parameter e is

calculated for favourable propagation conditions.
Agreed interpretation:

The parameter e is defined as the total distance along the path from the first to the last diffraction

edge. Under homogeneous conditions, straight lines are used as ray segments, while under favourable

conditions, arcs of uniform radius are used as ray segments. Different diffraction edges may be relevant

under homogeneous and favourable conditions respectively.
5.11 Diffraction under favourable conditions

Topic: CNOSSOS -EU: 2015 explains diffraction under favourable propagation conditions. The text

contains too little details to be unambiguous. In particular, the scale of Figure 2.5.f of CNOSSOS -EU:

2015 is chosen such that the ray segments appear to be straight lines while they should be arcs of radius

Γ, given by Equation (2.5.24) of CNOSSOS -EU: 2015.
Agreed interpretation:

Under favourable conditions, the propagation path in the vertical plane always consists of segments

of a circle whose radius is given by the 3D-distance between source and receiver according to

Equation (2.5.24) of CNOSSOS -EU: 2015, i.e. all segments of a propagation path have the same radius of

curvature. If the direct arc connecting source and receiver is blocked, the propagation path is defined

as the shortest convex combination of arcs enveloping all obstacles. Convex in this context means that

at each diffraction point, the outgoing ray segment is deflected downward with respect to the incoming

ray segment (see ISO 9613-1).

To illustrate the principle of constructing the ray path with multiple diffractions under favourable

conditions, Figure 2 is a slightly modified version of Figure 2.5.f of CNOSSOS -EU: 2015, scaled such that

the curvature of the rays is apparent.
4 © ISO 2020 – All rights reserved
---------------------- Page: 10 ----------------------
ISO/TR 17534-4:2020(E)

Figure 2 — Modified version of Figure 2.5.f of CNOSSOS -EU: 2015 showing ray paths

with easily visible curvature
5.12 Error in Figure 2.5.f and Equation (2.5.29) of CNOSSOS -EU: 2015
Topic: Figure 2.5.f and Equation (2.5.29) of CNOSSOS -EU: 2015 are erroneous.
Agreed interpretation:

Figure 2.5.f and Equation (2.5.29) of CNOSSOS -EU: 2015 treat the point O as a diffraction edge, even

though it lies below the rubber band. This is incorrect. Given the geometry displayed in Figure 2.5.f of

CNOSSOS -EU: 2015, the right-hand edge of obstacle E2 cannot be treated as a diffraction edge. A

corrected version of Figure 2.5.f of CNOSSOS -EU: 2015 is displayed as Figure 3, with Equation (2.5.29)

    
of C NOS S OS -E U: 2015 r e ad i n g : δ =+SO OO ++OO OR−SR .
F 11 22 33
Figure 3 — Corrected version of Figure 2.5.f of CNOSSOS -EU: 2015
5.13 Lateral diffraction

Topic: CNOSSOS -EU: 2015 introduces lateral diffraction, i.e. diffraction on vertical edge

...

TECHNICAL ISO/TR
REPORT 17534-4
First edition
Acoustics — Software for the
calculation of sound outdoors —
Part 4:
Recommendations for a quality
assured implementation of the
COMMISSION DIRECTIVE (EU)
2015/996 in software according to
ISO 17534-1
Acoustique — Logiciels de prévision de bruit dans l'environnement —
Partie 4: Recommandations pour l'assurance qualité de la mise
en œuvre de la DIRECTIVE (UE) 2015/996 de la COMMISSION
EUROPÉENNE dans les logiciels selon l'ISO 17534-1
PROOF/ÉPREUVE
Reference number
ISO/TR 17534-4:2020(E)
ISO 2020
---------------------- Page: 1 ----------------------
ISO/TR 17534-4:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii PROOF/ÉPREUVE © ISO 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/TR 17534-4:2020(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Identification of the official documentation ............................................................................................................................ 1

5 Uniform and agreed interpretation of ambiguities.......................................................................................................... 2

5.1 General ........................................................................................................................................................................................................... 2

5.2 Sloping objects ........................................................................................................................................................................................ 2

5.3 Equivalent heights ................................................................................................................................................................................ 2

5.4 Alternative statistical approach ............................................................................................................................................... 3

5.5 Octave band centre frequency f .............................................................................................................................................

m 3

5.6 Ground factor of the source area, G ......................................................................................................................................

S 3

5.7 Distances in Figure 2.5.b of CNOSSOS-EU: 2015 ......................................................................................................... 3

5.8 Equivalent heights in Equation (2.5.20) of CNOSSOS-EU: 2015 .................................................................... 3

5.9 Rayleigh’s Criterion ............................................................................................................................................................................. 4

5.10 Parameter e .................................................................................................................................................................................................4

5.11 Diffraction under favourable conditions .......................................................................................................................... 4

5.12 Error in Figure 2.5.f and Equation (2.5.29) of CNOSSOS-EU: 2015 ............................................................ 5

5.13 Lateral diffraction ................................................................................................................................................................................. 5

5.14 Reflection on nearly vertical objects .................................................................................................................................... 6

5.15 Retrodiffraction ...................................................................................................................................................................................... 6

6 Test cases ...................................................................................................................................................................................................................... 7

6.1 General ........................................................................................................................................................................................................... 7

6.2 Test cases with intermediate and final results ............................................................................................................ 8

6.2.1 TC01-TC03 — Flat ground with homogeneous acoustic properties ................................... 8

6.2.2 TC01 — Reflecting ground (G = 0).................................................................................................................... 8

6.2.3 TC02 — Mixed ground (G = 0,5) ......................................................................................................................... 9

6.2.4 TC03 — Porous ground (G = 1) ........................................................................................................................10

6.2.5 TC04 — Flat ground with spatially varying acoustic properties ........................................10

6.2.6 TC05 — Ground with spatially varying heights and acoustic properties ....................12

6.2.7 TC06 — Reduced receiver height to include diffraction in some frequency

bands .......................................................................................................................................................................................14

6.2.8 TC07 — Flat ground with spatially varying acoustic properties and long

barrier ....................................................................................................................................................................................17

6.2.9 TC08 — Flat ground with spatially varying acoustic properties and short

barrier ....................................................................................................................................................................................20

6.2.10 TC09 — Ground with spatially varying heights and and acoustic

properties and short barrier ..............................................................................................................................24

6.2.11 TC10 — Flat ground with homogeneous acoustic properties and cubic

building — Receiver at low height ................................................................................................................30

6.2.12 TC11 — Flat ground with homogeneous acoustic properties and cubic

object – receiver at large height .......................................................................................................................33

6.2.13 TC12 — Flat ground with homogeneous acoustic properties and

polygonal object — Receiver at low height ............................................................................................38

6.2.14 TC13 — Ground with spatially varying heights and acoustic properties

and polygonal object ........................................................................................................................................... .......42

6.2.15 TC14 — Flat ground with homogeneous acoustic properties and

polygonal object — Receiver at large height ........................................................................................47

6.2.16 TC15 — Flat ground with homogeneous acoustic properties and four buildings 53

6.2.17 TC16 — Reflecting barrier on ground with spatially varying heights and

acoustic properties .....................................................................................................................................................57

© ISO 2020 – All rights reserved PROOF/ÉPREUVE iii
---------------------- Page: 3 ----------------------
ISO/TR 17534-4:2020(E)
6.2.18 TC17 — Reflecting barrier on ground with spatially varying heights and

acoustic properties — Reduced receiver height................................................................................62

6.2.19 TC18 — Screening and reflecting barrier on ground with spatially varying

heights and acoustic properties .................. .....................................................................................................66

6.2.20 TC19 — Complex object and 2 barriers on ground with spatially varying

heights and acoustic properties .................. .....................................................................................................70

6.2.21 TC20 — Ground with spatially varying heights and acoustic properties ....................76

6.2.22 TC21 — Building on ground with spatially varying heights and acoustic

properties............................................................................................................................................................................78

6.2.23 TC22 — Building with receiver backside on ground with spatially varying

heights and acoustic properties .................. .....................................................................................................84

6.2.24 TC23 — Two buildings behind an earth-berm on flat ground with

homogeneous acoustic properties ................................................................................................................89

6.2.25 TC24 — Two buildings behind an earth-berm on flat ground with

homogeneous acoustic properties – receiver position modified ........................................94

6.2.26 TC25 — Replacement of the earth-berm by a barrier ...............................................................100

6.2.27 TC26 — Road source with influence of retrodiffraction .........................................................106

6.2.28 TC27 — Source located in flat cut with retro-diffraction .......................................................109

6.2.29 TC28 — Propagation over a large distance with many buildings between

source and receiver .................................................................................................................................................114

6.3 Summary of the final results .................................................................................................................................................121

7 Example of a template form for the declaration of conformity ....................................................................122

Bibliography .........................................................................................................................................................................................................................124

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ISO/TR 17534-4:2020(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

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

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.

A list of all parts in the ISO 17534 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
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ISO/TR 17534-4:2020(E)
Introduction

The structure of the ISO 17534 series is shown in Figure 1. ISO 17534-1 describes the general approach

of the ISO 17534 series, aiming to facilitate a standardized interpretation and a verifiably consistent

software implementation of outdoor sound calculation methods. ISO/TR 17534-2 contains general

recommendations for test cases and for a quality assurance interface. Further parts of the ISO 17534

series each address a specific outdoor sound calculation method for which they provide an agreed

interpretation of ambiguous aspects, a set of illustratuve test cases along with reference solutions, and

an example of a template form for the declaration of conformity for software developers.

This document addresses the calculation method laid down in the COMMISSION DIRECTIVE (EU)

2015/996, hereafter referred to as CNOSSOS -EU: 2015.

The European Commission developed Common NOise aSSessment methOdS (CNOSSOS-EU) for road,

railway, aircraft and industrial noise for the purpose of strategic noise mapping. CNOSSOS-EU aims at

improving the consistency and comparability of noise assessment results across the EU Member States

which are performed on the basis of the data becoming available through the consecutive rounds of

strategic noise mapping in Europe.
Figure 1 — Structure of the ISO 17534 series
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TECHNICAL REPORT ISO/TR 17534-4:2020(E)
Acoustics — Software for the calculation of sound
outdoors —
Part 4:
Recommendations for a quality assured implementation
of the COMMISSION DIRECTIVE (EU) 2015/996 in software
according to ISO 17534-1
1 Scope

This document facilitates a standardized interpretation and a verifiably consistent software

implementation of the sound propagation part of the calculation method CNOSSOS -EU: 2015 according to

ISO 17534-1. Other parts of CNOSSOS -EU: 2015, such as the source models or the calculation method for

aircraft noise, are beyond the scope of this document. This document provides an agreed interpretation

of ambiguous aspects of the sound propagation part of CNOSSOS -EU: 2015, a set of illustrative test cases

along with reference solutions, and an example of a template form for the declaration of conformity for

software manufacturers.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 17534-1, Acoustics — Software for the calculation of sound outdoors — Part 1: Quality requirements

and quality assurance

ISO/TR 17534-2, Acoustics — Software for the calculation of sound outdoors — Part 2: General

recommendations for test cases and quality assurance interface

COMMISSION DIRECTIVE (EU) 2015/996 of 19 May 2015 establishing common noise assessment

methods according to Directive 2002/49/EC of the European Parliament and of the Council, Official

Journal of the European Union, L 168/1
3 Terms and definitions

For the purposes of this document, the terms and definitions given in CNOSSOS -EU: 2015, ISO 17534-1,

and ISO/TR 17534-2 apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Identification of the official documentation

COMMISSION DIRECTIVE (EU) 2015/996 of 19 May 2015 establishing common noise assessment

methods according to Directive 2002/49/EC of the European Parliament and of the Council, Official

Journal of the European Union, L 168/1, herein referred to as CNOSSOS -EU: 2015.
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ISO/TR 17534-4:2020(E)

In its Chapter 2.5, “Calculation of noise propagation for road, railway, industrial sources”, CNOSSOS -EU:

2015 describes a method for calculating the attenuation of sound during propagation outdoors in order

to predict the levels of environmental noise at a distance from a variety of sources.

5 Uniform and agreed interpretation of ambiguities
5.1 General

The propagation of sound outdoors in CNOSSOS -EU: 2015 is calculated with a ray-based energetic model.

Attenuations are calculated in eight octave bands, and separately for two idealized meteorological

conditions labelled homogeneous and favourable. Finally, the A-weighted exposure level at a receiver

position is given as the weighted energetic sum over all sources, paths, meteorological conditions, and

octave bands.

Some aspects of the sound propagation model of CNOSSOS -EU: 2015 are not described in sufficient detail

to be unambiguous; in other aspects, in some part the official documentation is misleading. For each of

these problematic topics, an agreed interpretation is given in 5.2 to 5.15 to allow for a standardized

u nder s t a nd i n g of C NOS S OS -E U: 2015 .

The abbreviations are not explained when they are identical to those described in CNOSSOS -EU: 2015.

Symbols are not defined when they are identical to those applied in CNOSSOS -EU: 2015.

5.2 Sloping objects

Topic: CNOSSOS -EU: 2015 states in subclause 2.5.1 that “obstacles sloping, when modelled, more than

15° in relation to the vertical are out of the scope of this calculation method”. This restriction does not

constitute a general restriction of the method. Rather, it applies only to reflectors: obstacles sloping

more than 15° in relation to the vertical are not considered as reflectors.
Agreed interpretation:

Objects sloping more than 15° in relation to the vertical are not considered as reflectors, but are taken

into account in all other aspects of propagation such as ground effects and diffraction.

5.3 Equivalent heights

Topic: CNOSSOS -EU: 2015 states in subclause 2.5.3, under the headline "Significant heights above the

ground", that “If the equivalent height of a point becomes negative, i.e. if the point is located below

the mean ground plane, a null height is retained, and the equivalent point is then identical with its

possible image.” For points located below the mean ground plane, the equivalent height is set to zero in

the calculation of A . For the calculation of path length differences, it is irrelevant whether points

ground

lie above or below a mean ground plane, no points are shifted. For the calculation of Δ and

ground(S,O)

Δ special care has to be taken in the case that one of the respective end points lies below the

ground(O,R)
mean ground plane.
Agreed interpretation:

The first major step in the algorithm is to decide whether A or A must be calculated. The step

ground dif

is based on real coordinates, not equivalent heights. If a point lies below the mean ground plane, its

equivalent height is set to zero in the calculation of A . Equations (2.5.31) and (2.5.32) of CNOSSOS

ground

-EU: 2015 apply only in the most common case that both S and R lay above the mean ground plane. If

either S or R lies below the mean ground plane, the following simplified Equations apply:

Δ = A (CNOSSOS -EU: 2015, 2.5.31)
ground(S,O) ground(S,O)
Δ = A (CNOSSOS -EU: 2015, 2.5.32)
ground(O,R) ground(O,R)
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ISO/TR 17534-4:2020(E)

For the calculation of path length differences, the original coordinates are used and no points are

shifted, i.e. in the calculation of Δ the original heights of S and R are used.
dif(S,R)
5.4 Alternative statistical approach

Topic: CNOSSOS -EU: 2015 mentions in subclause 2.5.5, under the headline "Statistical approach inside

urban areas for a path (S, R)", a statistical approach for calculations inside urban areas beyond the

first line of buildings. This approach is not described in sufficient detail to be subjected to the quality

assurance methodology of ISO 17534-1.
Agreed interpretation:

A statistical approach is not appropriate in the calculation of sound propagation beyond the first line of

buildings.
5.5 Octave band centre frequency f

Topic: CNOSSOS -EU: 2015 is somewhat ambiguous about whether nominal centre frequencies or exact

centre frequencies should be used in the calculation of the atmospheric attenuation coefficient α .

atm
Agreed interpretation:

In the calculation of the atmospheric attenuation coefficient α , ISO 9613-1 is followed, and exact centre

atm

frequencies are used. In all other calculations, the nominal centre frequency, denoted f , are used.

The tabulated values in ISO 9613-1 are based on the pressure at sea level.
5.6 Ground factor of the source area, G

Topic : C NOS S OS -E U: 2015 i nt r o duc e s G in subclause 2.5.6 as the ground factor G of the source area. For

industrial sources, it is left open how exactly G is to be calculated.
Agreed interpretation:

For industrial point sources, G is calculated as the average of the ground factor G over a distance of 1 m

beginning at the vertical projection point below the source and proceeding along the direction source-

receiver.
5.7 Distances in Figure 2.5.b of CNOSSOS -EU: 2015

Topic: In CNOSSOS -EU: 2015, it is unclear whether the distances d displayed in Figure 2.5.b are

3D-distances along the ground or 2D-projection onto a horizontal plane.
Agreed interpretation:

Figure 2.5.b displays a 2D-projection onto the horizontal plane. The distances d used in the calculation

of G are measured in this horizontal plane.
path
5.8 Equivalent heights in Equation (2.5.20) of CNOSSOS -EU: 2015

Topic: CNOSSOS -EU: 2015 explains that modified equivalent heights should be used in the calculation of

A . But it is unclear whether these modified equivalent heights or unmodified equivalent heights

ground,F

should be used in the calculation of A according to Equation (2.5.20) of CNOSSOS -EU: 2015.

ground,F,min
Agreed interpretation:

Unmodified equivalent heights are used in the calculation of A according to Equation (2.5.20)

ground,F,min
of C NOS S OS -E U: 2015 .
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ISO/TR 17534-4:2020(E)
5.9 Rayleigh’s Criterion

Topic: CNOSSOS -EU: 2015 states that no diffraction should be calculated if the ray path passes "high

enough" over the diffraction edge. In this context, CNOSSOS -EU: 2015 refers to Rayleigh’s Criterion

without providing details or formulae. The circumstances under which diffraction is calculated should

be defined unambiguously.
Agreed interpretation:

In the unique vertical plane containing source and receiver, the line of sight from source to receiver

is defined, under homogeneous conditions, as the straight line connecting source and receiver. Under

favourable conditions, the line of sight is defined as the arc of radius Γ, given by Equation (2.5.24) of

CNOSSOS -EU: 2015, connecting source and receiver.

The decision whether diffraction must be calculated is made separately for homogeneous and favourable

conditions respectively. If the line of sight is blocked, diffraction is always calculated. If the line of sight

from source to receiver is unobstructed, Rayleigh’s Criterion is employed as follows: first, that point

D of the terrain profile including obstacles is identified, which gives the largest δ , i.e. the δ with the

D D

smallest absolute value. Then δ * is calculated as the path length difference from S’ to R’ via D, where S’

and R’ are the respective images of source and receiver constructed with the appropriate mean ground

planes containing source or receiver. Diffraction is calculated only if δ > -λ/20 and δ > λ/4 - δ *

D D D

(Rayleigh’s Criterion), where λ is the wavelength at the nominal centre frequency and calculated with a

speed of sound of 340 m/s.
5.10 Parameter e

Topic: CNOSSOS -EU: 2015 introduces the parameter e as the total distance along the path from the first

to the last diffraction edge according to the "rubber band method". It is unclear how the parameter e is

calculated under favourable propagation conditions.
Agreed interpretation:

The parameter e is defined as the total distance along the path from the first to the last diffraction

edge. Under homogeneous conditions, straight lines are used as ray segments, while under favourable

conditions, arcs of uniform radius are used as ray segments. Different diffraction edges may be relevant

under homogeneous and favourable conditions respectively.
5.11 Diffraction under favourable conditions

Topic: CNOSSOS -EU: 2015 explains diffraction under favourable propagation conditions. The text

contains too little details to be unambiguous. In particular, the scale of Figure 2.5.f of CNOSSOS -EU:

2015 is chosen such that the ray segments appear to be straight lines while they should be arcs of radius

Γ, given by Equation (2.5.24) of CNOSSOS -EU: 2015.
Agreed interpretation:

Under favourable conditions, the propagation path in the vertical plane always consists of segments

of a circle whose radius is given by the 3D-distance between source and receiver according to

Equation (2.5.24) of CNOSSOS -EU: 2015, i.e. all segments of a propagation path have the same radius of

curvature. If the direct arc connecting source and receiver is blocked, the propagation path is defined

as the shortest convex combination of arcs enveloping all obstacles. Convex in this context means that

at each diffraction point, the outgoing ray segment is deflected downward with respect to the incoming

ray segment (see ISO 9613-1).

To illustrate the principle of constructing the ray path with multiple diffractions under favourable

conditions, Figure 2 is a slightly modified version of Figure 2.5.f of CNOSSOS -EU: 2015, scaled such that

the curvature of the rays is apparent.
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ISO/TR 17534-4:2020(E)

Figure 2 — Modified version of Figure 2.5.f of CNOSSOS -EU: 2015 showing ray paths

with easily visible curvature
5.12 Error in Figure 2.5.f and Equation (2.5.29) of CNOSSOS -EU: 2015
Topic: Figure 2.5.f and Equation (2.5.29) of CNOSSOS -EU: 2015 are erroneous.
Agreed interpretation:

Figure 2.5.f and Equation (2.5.29) of CNOSSOS -EU: 2015 treat the point O as a diffraction edge, even

though it lies below the rubber band. This is incorrect. Given the geometry displayed in Figure 2.5.f of

CNOSSOS -EU: 2015, the right-hand edge of obstacle E2 cannot be treated as a diffraction edge. A

corrected version of Figure 2.5.f of CNOSSOS -EU: 2015 is displayed as Figure 3, with Equation (2.5.29)

    
of C NOS S OS -E U: 2015 r e ad i n g : δ =+SO OO ++OO OR−SR .
F 11 22 33
Figure 3 — Corrected version of Figure 2.5.f of CNOSSOS
...

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