Sound quality evaluation of air-conditioning sounds in a vehicle using psychoacoustic parameters

With recent developments of noise reduction technologies from mechanical components of a vehicle, air-conditioning systems become a major noise source in the compartment of a vehicle. To improve quietness in the compartment further, it is important not only to reduce the sound pressure level (SPL), but also to improve the sound quality. In this study, we tried to evaluate the air-conditioning sounds from a viewpoint of sound quality. First, we carried out a subjective evaluation experiment using some evaluation words that represent characteristics of the air-conditioning sounds. As a result of a factor analysis, noting that the air-conditioning sounds can be explained by three factors of "rough," "space" and "refreshing." "Rough factor" has strong correlation with the SPL, however, "space factor" and "refreshing factor" have little correlation with SPL. Next, to investigate parameters that correlate with these factors, we carried out an experiment to evaluate the air-conditioning sounds using the psychoacoustic parameters of loudness and sharpness. As a result, noting that "rough" factor strongly correlates with loudness, "space" and "refreshing" factors correlate with sharpness. This result shows that it is possible to evaluate the air-conditioning sounds a viewpoint of sound quality by using the sharpness that is different from SPL.