ISO 13472-2:2025
(Main)Acoustics — Measurement of sound absorption properties of road surfaces in situ — Part 2: Spot method for reflective surfaces
Acoustics — Measurement of sound absorption properties of road surfaces in situ — Part 2: Spot method for reflective surfaces
This document 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. If necessary for practical applications the diameter of the tube can be reduced to 80 mm. This will increase the upper boundary of the frequency range to 2 000 Hz one-third octave band (see REF Section_sec_5.4 \r \h 5.4 08D0C9EA79F9BACE118C8200AA004BA90B020000000800000010000000530065006300740069006F006E005F007300650063005F0035002E0034000000 ) but reduces the area under test. The test method is intended for the following applications: — determination of the sound absorption coefficient (and, if of interest, also the complex acoustical impedance) of semi-dense to dense road surfaces; — determination of the sound absorption properties of test tracks according to ISO 10844[ REF Reference_ref_4 \r \h 2 08D0C9EA79F9BACE118C8200AA004BA90B0200000008000000100000005200650066006500720065006E00630065005F007200650066005F0034000000 ] or other similar standards and test surfaces defined in national and international type approval regulations for road vehicles and their tyres; — verification of the compliance of the sound absorption coefficient of a road surface with design-specifications or other requirements.
Acoustique — Mesurage in situ des propriétés d'absorption acoustique des revêtements de chaussées — Partie 2: Méthode ponctuelle pour les surfaces réfléchissantes
General Information
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Standards Content (Sample)
International
Standard
ISO 13472-2
Second edition
Acoustics — Measurement of sound
2025-05
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 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle of the method . 3
4.1 Measurement principle .3
4.2 Signal analysis . .4
4.3 In situ fixture .4
5 Test equipment . 5
5.1 Components of the test system .5
5.2 Sound source .5
5.3 Test signal .5
5.4 Impedance tube .5
5.4.1 Tube diameter .5
5.4.2 Tube length and microphone positions .5
5.4.3 Microphones .6
5.5 In situ test fixture between impedance tube and test surface .6
5.6 Signal processing system .7
5.7 Thermometer and barometer .7
6 Measurement and analysis requirements . 7
6.1 Stabilizing the system .7
6.2 Calibration of the system .7
6.3 Reference measurement .7
6.4 Measurement of a road surface .7
6.5 Data analysis .8
6.6 One-third octave band absorption spectrum .9
7 Positioning of the equipment . 9
7.1 Location of the measurement positions .9
7.1.1 Test surfaces such as those meeting ISO 10844 requirements .9
7.1.2 Regular roads .9
7.2 Temperature .9
8 Measurement and analysis procedure . 9
9 Measurement uncertainty requirements . 10
10 Test report .11
Annex A (informative) Correction on base of reference measurement .13
Annex B (informative) Measurement uncertainty . 14
Annex C (informative) Alternative procedures to improve accuracy . 17
Annex D (informative) In situ test fixture .20
Annex E (informative) Example of a test report .22
Bibliography .25
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.
This second edition cancels and replaces the first edition (ISO 13472-2:2010), which has been technically
revised.
The main changes are as follows:
— mandatory choice of the transfer function formulation and quality requirements for the coherence
function;
— an alternative microphone arrangement and application of alternating transfer functions are presented
to cancel the distortion due to destructive interference at the microphone positions.
A list of all parts in the ISO 13472 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.
iv
Introduction
This method provides a means to evaluate the sound absorption characteristics of a road surface without
damaging the surface. The field of application is limited to low absorption surfaces such as those in
[2]
accordance with ISO 10844 and similar surfaces. Due to air leakage the method is not reliable if the
measured sound absorption coefficient exceeds 0,15. Surfaces with a sound absorption coefficient of 0,10 or
below are considered reflective.
The method in this document is based on propagation of the test signal from the source to the road surface
and back to the receiver through an impedance tube with a diameter of 80 mm to 100 mm. The tube covers
2 2
an area of approximately 0,005 m to 0,008 m and a frequency range, in one-third octave bands, from
250 Hz to 1 600 Hz for a 100 mm diameter, or from 250 Hz to 2 000 Hz, for an 80 mm diameter tube. It uses
the test procedure and signal processing described in ISO 10534-2, but because of the defined frequency
range of application, the dimensions of the system are not freely adjustable.
The essential part in the ISO 10534-2 procedure is the determination of the transfer function between two
microphones at different distances from the sample at the end of the tube. In this case of a reflecting sample
at specific frequencies destructive interferences (nodes) will occur at the microphone positions jeopardizing
the correct determination of the transfer function between the microphone pair.
Therefore in this document the ISO 10534-2 procedure is extended with a preference for transfer function
H calculated as the ratio of the auto spectrum S at the lowest microphone position and the cross
spectrum S and requirements on the resolution, the sample frequency and the block length in the FFT
analysis added with a requirement on the average narrow band coherence within a one-third octave band.
Recommendations for improvement of the accuracy by alternative microphone arrangement, variation in
transfer function and type of random noise are presented in Annex C.
[3]
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.
B
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