ISO 13472-2:2010

INTERNATIONAL ISO
STANDARD 13472-2
First edition
2010-05-15
Acoustics — Measurement of sound
absorption properties of road surfaces in
situ —
Part 2:
Spot method for reflective surfaces
Acoustique — Mesurage in situ des propriétés d'absorption acoustique
des revêtements de chaussées —
Partie 2: Méthode ponctuelle pour les surfaces réfléchissantes

Reference number
©
ISO 2010
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

©  ISO 2010
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2010 – All rights reserved

Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Normative references.1
3 Terms and definitions .2
4 Principle.2
5 Test equipment.4
5.1 Components of the test system.4
5.2 Sound source.4
5.3 Test signal.4
5.4 Impedance tube .4
5.4.1 Tube diameter.4
5.4.2 Tube length and microphone positions.5
5.5 Microphones .6
5.6 In-situ test fixture between impedance tube and test surface.6
5.7 Signal-processing system.6
5.8 Thermometer and pressure measurement .6
6 Measurement and analysis procedure .6
6.1 Stabilizing the system.6
6.2 Calibration of the system.7
6.3 Reference measurement.7
6.4 Background noise measurement.7
6.5 Measurement of a road surface .7
6.6 Data analysis.8
7 Positioning of the equipment.8
7.1 Location of the measurement positions .8
7.1.1 Test surfaces such as those meeting ISO 10844 requirements .8
7.1.2 Regular roads.8
7.2 Condition of the road surface .8
7.3 Temperature.8
8 Measurement and analysis procedure .8
9 Measurement uncertainty.9
10 Test report.11
Annex A (normative) Correction on base of reference measurement .12
Annex B (informative) Measurement uncertainty .13
B.1 General.13
B.2 Expression for the calculation of the absorption coefficient .13
B.3 Sources of uncertainty.14
B.4 Expanded uncertainty of measurement.15
Annex C (informative) Sketch of in-situ test fixture .16
Annex D (informative) Example of a test report.18
Bibliography.20

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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 13472-2 was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.
ISO 13472 consists of the following parts, under the general title Acoustics — Measurement of sound
absorption properties of road surfaces in situ:
⎯ Part 1: Extended surface method
⎯ Part 2: Spot method for reflective surfaces
iv © ISO 2010 – All rights reserved

Introduction
This part of ISO 13472 specifies a test method for measuring in situ the sound absorption coefficient of road
surfaces as a function of frequency under normal incidence.
This method enables evaluation of the sound absorption characteristics of a road surface without damaging
the surface. It is intended to be used to qualify the absorption characteristics of road surfaces used for vehicle
and tyre testing. It may also be used during road construction, road maintenance, and other traffic noise
studies. However, the field of application is limited to low absorption surfaces.
The method specified in this part of ISO 13472 is based on propagation of the test signal from the source to
the road surface and back to the receiver through an impedance tube. The tube covers an area of

approximately 0,008 m and a frequency range, in one-third-octave bands, from 250 Hz to 1 600 Hz. It uses
the test procedure and signal processing specified in ISO 10534-2, but because of the defined frequency
range of application, the dimensions of the system are not adjustable, but fixed.
This method is primarily intended for smooth low absorption surfaces, such as those in accordance with
ISO 10844. The method is not reliable if the measured sound absorption coefficient exceeds 0,15. Surfaces
with values above 0,10 are not considered to be reflective.
[5]
This method is complementary to the extended surface method (ISO 13472-1 ) that covers an area of
approximately 3 m and a frequency range, in one-third-octave bands, from 250 Hz to 4 000 Hz.
Both methods should give similar results in the frequency range from 315 Hz to 1 600 Hz, but their fields of
[5]
application and therefore their accuracy differ strongly. The method described in ISO 13472-1 has limited
accuracy at small sound absorption values and is therefore unsuitable for checking compliance of surfaces
with the requirements of such documents as ISO 10844, while the method specified here fails at higher sound
absorption values.
Within their ranges, the methods are also applicable to acoustic materials other than road surfaces.
The measurement results of this method are comparable to the results of the impedance tube method,
[4]
performed on bore cores taken from the surface in accordance with documents such as ISO 10534-1 ,
[7]
ISO 10534-2 and ASTM E1050 .
The measurement results obtained with this method are in general not comparable to the results of the
[1]
reverberation room method (ISO 354 ), because the method described in this part of ISO 13472 uses a
plane progressive wave at perpendicular incidence, while the reverberation room method uses a diffuse sound
field.
INTERNATIONAL STANDARD ISO 13472-2:2010(E)

Acoustics — Measurement of sound absorption properties of
road surfaces in situ —
Part 2:
Spot method for reflective surfaces
1 Scope
This part of ISO 13472 specifies a test method for measuring in situ the sound absorption coefficient of road
surfaces for the one-third-octave-band frequencies ranging from 250 Hz to 1 600 Hz under normal incidence
conditions. For special purposes, the frequency range can be changed by modifying the dimensions of the
system.
The test method is intended for:
a) determination of the sound absorption coefficient of semi-dense to dense road surfaces (and, if of interest,
also the complex acoustical impedance);
b) determination of the sound absorption properties of test tracks in accordance with standards such as
ISO 10844 and test surfaces defined in national and international type approval regulations for road
vehicles and vehicle tyres;
c) verification of the compliance of the sound absorption coefficient of a road surface with design
specifications or other requirements.
2 Normative references
The following referenced documents are indispensable for the application 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 10534-2:1998, Acoustics — Determination of sound absorption coefficient and impedance in impedance
tubes — Part 2: Transfer-function method
ISO 10844, Acoustics — Specification of test tracks for measuring noise emitted by road vehicles and their
tyres
ISO/IEC Guide 98-3:2008, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
IEC 61260, Electroacoustics — Octave-band and fractional-octave-band filters
3 Terms and definitions
For the purposes of this document, the following definitions apply.
3.1
frequency range
frequency interval in which measurement
...