Perception of rolling noise

Licentiate thesis, 2015

Due to improvements on combustion-engines and electric-engines for cars, tyre noise has become the prominent noise source at low and medium speeds. Models exist that simulate the noise produced by a rolling tyre, as do models that auralize different traffic situations from a basic data set. When constructing a tyre it is of interest if improvements and planned changes are not only physically measurable, but that they also can be perceived. Focussing on that, two aims were followed in this thesis. The first aim was to combine an established model for tyre noise (SPERoN) with an auralization tool. The combined model can predict the spectrum of the sound at 7.5 m, as well as reproduce the sound for a given listener position. The auralization uses a methodology where recorded sounds are converted to source signals for engine and tyre/road-interaction. These can be shaped by the spectra estimated in SPERoN and synthesized back into a pass-by signal. Psychoacoustic judgements were used to compare the modelled signals with recorded signals. To see how well the modelled signals match the real recorded signals for perception, two listening-tests were performed. The simulated and recorded signals were rated by pleasantness, loudness, roughness and sharpness using semantic differentials. It was found that responses for simulated and recorded signals correlate for all cases, but rankings could not be reproduced exactly. The model can be further improved to be more applicable for listening tests. The model has been optimized after a first validation. The second aim laid focus on the perception of tyre/road noise. When designing tyre sounds, the main aim should be to increase the pleasantness of the total vehicle sound while maintaining the carried information and reducing the sound level. To be able to do this an understanding of how physical changes in a tyre are reflected in the perception of the same tyre is essential. Thus, the second aim was to see if the rolling noise of a tyre can be both differentiated and characterized by its perceptual qualities. The focus is on the perception of the sound outside the car, perceived by for example a pedestrian. Listeners have judged different road tyre combinations and their perception in terms of their emotional responses (pleasantness, activation and stress) and their psychoacoustic responses (loudness, sharpness, roughness, and pitch). The results confirmed that rolling noise can be perceptually differentiated. It is further possible to differentiate between the effects of the street and the effects of the tyre on all emotional and most psychoacoustic parameters. The results suggest that changes to road surfaces or tyres can affect both emotional and psychoacoustic perceptual qualities.