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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.

The Hybrid FE-SEA method is a recently developed numerical technique that deals with the so-called mid-frequency problem. Such problems involve the dynamic analysis of systems that include, at the same frequency range, components with high and low modal density. Systems with a reduced number of modes are usually modeled using deterministic methods, as the Finite Element (FE) Method, while modal dense systems need to be treated by means of statistical methods such as the Statistical Energy Analysis (SEA). Neither FE nor SEA can properly describe a system that displays the mid-frequency behavior due to a prohibitive computational cost (FE) or the lack of accuracy (SEA). The floor structure of an aircraft is a typical case of a mid frequency problem, where the floor beams are relatively rigid and have very few modes while the floor panels have a very high modal density.