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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.

This paper presents an objective evaluation using order analysis to quantify the noise levels generated by the pumps of the power steering system mounted on a test stand and operating under two pressure load conditions (5 and 50 bar) in the working range between 500 and 5.000 rpm. Also, under these conditions experimental tests are carried out to verify the influence of the output pulsating pressure of the pump on the noise and vibration measurements.

In this study an objective metric is presented to evaluate the hiss noise of hydraulice power steering. The correlation between subjective tests and psychoacoustics metrics is investigated. The objective metric is obtained using multilinear regression where the psychoacoustics metric and the results of the subjective tests are the dependent and independent variables of the linear regression, respectively.