Perceived sound character and objective properties of powertrain noise in car compartments

Sounds from automotive powertrains often have tonal components, due to periodically fluctuating parameters in the structure. In this study a single authentic car noise, recorded binaurally in a car compartment, was used for synthesis of single tone in background noise during acceleration. Three aspects of the tone were altered, length (half, same, double) amplitude (-6, -3, 0, 3, 6, 9 dB change) and amplitude modulation frequency (0, 1, 2, 4, 8, 16, 32, 64, 128 Hz). The frequency of the tone followed an order of a revolution speed, which was also recorded. In a listening test, where sounds were rated on adjective scales, significant difference could be shown with the sound series as within group factor for most adjectives. Principal Component Analysis (PCA) was used for grouping the adjectives into five dimensions interpreted as: quality, audibility, tonal content, modulation and safety. The obtained dimensions were shown to be reliable. With means over the adjectives in each dimension for all the sounds, relationships between the physical differences and the dimensions and the three series of change were found. This research will enable a deeper understanding of subjective dimensions underlying acoustical factors important for perceived sound quality. The findings may therefore be used in future design approaches improving the perceived sound quality in the automotive industry