Browsing by Author "Swart, Daniel Johannes"

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    The psychoacoustics of electric vehicle signature sound
    (Stellenbosch : Stellenbosch University, 2018-03) Swart, Daniel Johannes; Bekker, Annie; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: The automotive industry is currently exploring the global sound sphere to identify a pleasant, safe and unique electric vehicle signature sound. Drive-train acoustics contribute to the performance benchmark of vehicles in the marketplace. Electric vehicle sound signatures differ vastly from those of internal combustion engines. Questions arise as to how these signature sounds relate to consumer experiences, and how the positive attributes of these sounds can be extracted and enhanced. The presented work aimed to investigate the objectively and subjectively evaluated attributes of electric vehicle signature sound, and the associated consumer satisfaction. A subjective evaluation procedure for the classification of the noise produced by electric vehicles was adapted from existing methodologies for internal combustions engines. Itwas found that ‘Calm’, ‘Deep’, ‘Rumbling’,‘Creative’ and ‘Futuristic’ semantics should be added to existing tests to typically describe electric vehicle sound character. The sound signatures of six standard production electric vehicles and one hybrid electric vehicle were benchmarked through constant speed andWide Open Throttle drives. Time and frequency domain analyses were used to compare the different vehicles, and results revealed that electric vehicles contain substantial sound energy in the upper frequency bands due to the tonal components. Lower sound pressure levels were achieved in a multi-stage gearbox, with regards to the high frequency content associated with electric motors. High Prominence Ratio levels, in excess of 10 dB,were found for electric vehicles and current literature points to diminished consumer satisfaction as a result. Furthermore, standard production electric vehicle sound signatures were evaluated against enhanced sound stimuli, based on subjective semantics and objective metrics, to determine the dimensions of electric vehicle sound quality that can lead to improved consumer satisfaction. The methodologywas to undertake two independent subjective evaluations, performed by a jury of 32 and 52 members respectively, to determine the perceived electric vehicle sound experience. Results showed that Sharpness is fundamental to governing the electric vehicle sound experience. Secondly, the underlying dimensions of electric vehicle sound quality are sparsely described in literature and was therefore investigated. A factor analysis found that additional to the dimensions of refinement and powerfulness of internal combustion vehicle sound, electric vehicles also have a third dimension associated with a ‘Futuristic’ factor. Lastly, a consumer satisfaction model was proposed through multiple linear regression and the 95th percentile Sharpness value. The model yielded promising results for both interior and motorbay sound signatures and is proposed as a means of gauging consumer satisfaction for electric vehicle sound quality. The complexity of electric vehicle sound character was discussed and recommendations were offered with respect to the design considerations of future electric vehicle sound signatures. A holistic approach regarding both subjective and objective evaluation methods is recommended for future electric vehicle research, in order to fully understand the attributes that govern electric vehicle sound quality.