Knabben, R., Triches, G., Villena, J., Greges, S. et al., "Tyre-Road Noise and Sound Absorption of Different Road Types," SAE Technical Paper 2012-36-0616, 2012, doi:10.4271/2012-36-0616.
The generation and propagation of noise from vehicles is governed by several different mechanisms, but it is mainly produced by motor vibration at speeds below 50 km/h and the tyre/pavement contact at speeds above 50 km/h. In the latter case the noise can be mitigated through the use of special asphalt mixes. This study evaluates the sound absorption coefficient, using the impedance tube method, of different types of asphalt mixes (common dense asphalt mix, dense mix with asphalt-rubber, coating of drainage mix with voids and porous friction layer, the latter two with rubber asphalt). The results show that the sound absorption coefficient is dependent on the volume of total and interconnecting voids as well as the thickness of the sample.