Sound quality evaluation on folding sound of vehicle door mirror

Most of passenger vehicles have the door mirrors that can be folded by electric motors. The folding drive sound is one of the target to enhance its sound quality to be quieter and pleasant. The main objective of this research is to determine a metric that describes the subjective perception of the listeners in terms of pleasantness. For this purpose, we have measured four different exterior mirrors in a semi-anechoic room using an acoustic dummy head and conducted subjective evaluation test. Two different psychoacoustic tests, pairwise comparison and ranking procedure, were performed in three institution locates in Japan, Spain and Portugal in order to obtain a subjective evaluation cross-culturally. Thirteen to twenty-six people with normal hearing were participated in each experiment. The result showed that the pleasantness evaluations were not dependent on the equivalent A-weighted sound pressure level of the stimuli but seemed to be related with the level of their stationary (middle) part and the quality of ending part. Then, we conducted the second experiment using the stimuli adjusted sound level equally and divided into three different durations; middle parts, starting and middle parts, and middle and ending part; in order to examine the effect of sound quality of each part on the total impression. The results were also discussed in comparison with some sound quality metrics such as loudness, sharpness, fluctuation strength, and roughness.