Design of alert sound for electric vehicle based on fluctuation strength for amplitude fluctuation

The motor sound of an electric vehicle is quiet at low speeds. Thus, it is difficult for pedestrians to detect vehicles approaching them. This is not only a particular problem for visually impaired people but also for any people who cannot see the approaching vehicle, for example, in a situation where the vehicle comes from behind or an obstacle object. Therefore, the vehicle was designed to provide an alert sound to solve this problem. The UN Regulation No.138 on Quiet Road Transport Vehicles was adopted and published in 2016. The regulation introduces a minimum sound level, spectrum, and frequency shift depending on the speed of the vehicle. However, the regulation of the amplitude fluctuation has not been defined. In this study, it is assumed that pedestrians are aware of approaching gasoline vehicles by hearing the amplitude fluctuations in the exhaust sound. We propose that they can be aware of approaching EV by hearing amplitude fluctuation sounds. Our previous studies found that fluctuation frequency, non-periodic fluctuation, and amplitude envelope influence the sensation of hearing fluctuation or fluctuation strength. Their effects on pedestrian detectability were assessed in an actual environment. The results indicate that these characteristics are effective in detecting approaching vehicles.