Subjective evaluation of vehicle door mirror noises with differing clearances between parts

As a part of a study on the effects of mounting conditions of vehicle door mirror on aerodynamic noise, hearing impression of the noises were examined by a series of subjective evaluations. We focused on the difference of aerodynamic noise caused by the differing clearance between the mounting base and door panel, and that between the base and mirror visor. To examine the effects of these clearances on hearing impression, a series of subjective evaluation experiments were conducted. The aerodynamic noises were recorded in a wind tunnel using several mirror models that had different clearances. The acoustic transfer function between door mirror and ear position of a driver, which was previously measured, was convoluted to the recorded noises. To evaluate the relative difference on hearing impression, we conducted a similarity evaluation using paired-comparison method (Experiment 1). As the result of the first experiment, we obtained two-dimensional hearing impression space, then we confirmed the significant difference between the mounting clearances. The relative positions of stimuli on the impression space indicated that the impression was affected not only by A-weighted sound pressure level but also the other aspects. To confirm the qualitative meaning of the relative difference, the other experiment using semantic differential (SD) method was conducted (Experiment 2). The relationship between the hearing impression space and the rating values of SD-scales was discussed by the multi-regression analysis. The results suggested that a larger clearance between the mounting base and mirror visor resulted a noisy and bright impression.