DIN ISO 13472-2:2010-12

DIN ISO 13472-2 specifies a test method for measuring in situ the sound absorption coefficient of road surfaces as a function of frequency under normal incidence. The measurement method enables evaluation of the sound absorption characteristics of a road surface without damaging the surface. It is intended to be used to describe 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 DIN ISO 13472-2 is based on propagation of a test signal from the sound source to the road surface and back to the receiver through an impedance tube. The impedance tube covers an area of approximately 0,008 m² and a frequency range, in one-third-octave bands, from 250 Hz to 1 600 Hz. The test method follows 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. The method is primarily intended for smooth low absorption road surfaces, such as those constructed 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. This method is complementary to the extended surface method (ISO 13472-1 [5]) that covers an area of approximately 3 m² 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 application and therefore their accuracy differ strongly. The method described in ISO 13472-1 [5] 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 in DIN ISO 13472-2 fails at higher sound absorption values. Within their application ranges, the methods are also applicable to the determination of acoustic properties of materials other than those used on road surfaces. The measurement results of the method given in DIN ISO 13472-2 are comparable to the results of the impedance tube method, performed on bore cores taken from the surface in accordance with documents such as ISO 10534-1 [4], ISO 10534-2 and ASTM E1050 [7]. The measurement results obtained with the method given in DIN ISO 13472-2 are, in general, not comparable to the results of the reverberation room method (ISO 354 [1]), because the method described in DIN ISO 13472-2 uses a plane progressive wave at perpendicular incidence, while the reverberation room method uses a diffuse sound field. The methods of DIN ISO 13472-2 are 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. The International Standard ISO 13472-2, on which DIN ISO 13472-2 is based, has been prepared by ISO/TC 43/SC 1/WG 38 "Procedure for measuring sound absorption properties of road surfaces - In-situ method", with the German collaboration of Subcommittee NA 001-01-05-03 UA "Road vehicles - Characteristics" of Working Committee NA 001-01-05 AA "Geräuschemissionsmessungen an Fahrzeugen einschließlich Messungen im Fahrgastraum und am Arbeitsplatz" ("Measurement of noise emission on vehicles, including measurements in the vehicle's interior and workplace").