Subjective evaluations of detectability of alert sound for electric and hybrid electric vehicle under actual environment

The motor sound on electric and hybrid electric vehicle is quiet at low speeds. Thus, pedestrians have difficulty detecting those vehicles approaching them. Although those vehicles were designed to play an alert sound to solve this problem, it has not been solved yet. Our previous studies found that the fluctuation frequency, non-periodic fluctuation and amplitude envelope are effective to make them detect approaching vehicles. However, those studies were investigated under only an actual environment, weren't examined validity of detectability in those studies. Therefore, this paper investigate under some actual environment, examine the validity. Investigations were carried out by using synthesized complex sounds which were designed to have periodic and non-periodic amplitude fluctuations. Those complex sounds have characteristics of amplitude fluctuations in gasoline powered vehicle. Envelopes such as modulation wave in amplitude-modulated sound were set for deviations for time and amplitude, and amplitude-modulated complex sounds were synthesized using sine wave, sawtooth wave, and rectangle wave as modulation wave. Then, their effects on detectability by pedestrians were assessed in some actual environment. The results found that amplitude fluctuation enhances the ability with which people detect approaching electric and hybrid electric vehicles in case of some complex sound.