Tyre-road noise measurements: influence of tyre tread and road characteristics

Traffic noise is a well known problem. For speeds above approximately 40 km/h the noise is mostly tyre-road noise. The noise level depends on the tyre, the road and the interaction between the tyre and the road. There are various well-known methods to measure tyre-road noise and in this paper the measurement results of CPX, impedance tube and road roughness measurements are combined to investigate the relation between the radiated noise and the tyre tread design and road characteristics. All measurements have taken place on a special test area at Airport Twente, where 8 different type of asphalt surfaces were constructed. Two these tracks are based on new models for sound absorption and grip. Six of the tracks are porous asphalt concrete. To investigate the relation between tyre tread design and the sound radiation, three simple parameters are defined based on properties that are commonly considered when researching the influence of tyre tread. However, the parameters defined in this paper are simplified, such that they can be applied when no detailed knowledge of the tyre properties is available. The relation between road characteristics and sound radiation is investigated using the properties of the road, such as stone size, porosity and sound absorption, and some texture parameters as defined by the International Organisation of Standardization (ISO). The correlation between the tyre and road parameters and the sound radiation is investigated, both for the root mean square values and the octave bands of 500 Hz, 1000 Hz and 2000 Hz. The results show that both the tyre parameters as the road characteristics, such as porosity of the road and the sound absorption by the road, are important for a decrease in sound radiation. The influence of the porosity of the road and the sound absorption by the road on the radiated sound is more significant for the frequencies in the octave band of 2000 Hz than the influence of the investigated tyre treads on the radiated sound. However, in the octave band of 1000 Hz, the influence of the tyre tread parameters on the sound radiation is larger. Furthermore, a relation is found between the radiated sound and the maximum stone sizes in the asphalt concrete. The measurements show a clear correlation between the sound absorption of the tested tracks and the radiated sound: for an increasing sound absorption coefficient the sound radiation decreases. Moreover, the total sound radiation decreases more when the sound absorption of higher frequencies is increased.