Energy distribution for sournd quality improvement of exhaust noise of crusier type of motorcycle

Abstract

The demand for motorcycles has seen steady growth in recent years. For motorcycles, as well as automobiles in general, sound quality (SQ) is one of the important factors affecting riding comfort. Thus, as with the wider field of automobile manufacturing, motorcycle manufacturers regard SQ-based noise control as a useful tool for improving competitiveness and popularity in the global commercial market. Among the numerous parts of a motorcycle, the exhaust system is the key to determining the SQ, as well as its performance. In this study, the distribution of the exhaust noise energy of a cruiser type of motorcycle in the frequency domain was proposed to improve its SQ. To this end, the audible frequency range was divided into three bands based on its effect on the perceptual feeling described as pleasant. To obtain a desirable energy distribution, a subjective listening experiment based on a semantic differential method was conducted with the modified exhaust noises by changing the band level of each division of the frequency band. A hierarchical clustering analysis and factor analysis were applied to the results of the subjective experiment in order to determine the relation between the subjective feeling and the variation in the spectral shapes of the exhaust noises. The results showed that perceptual feelings described as pleasant, expensive, and classic were strongly influenced by a change in the band level in the low-frequency range below 300 Hz, whereas the hard and crispy perceptions were influenced in the high-frequency range above 1 kHz. To quantitatively represent such situations, the energy ratio and partial-loudness ratio representing the energy balance were defined and calculated. Finally, it was found that a larger energy ratio or partial-loudness ratio resulted in a better SQ for the exhaust noise of the cruiser type of motorcycle.