Emotional Effect of Car Interior Sounds: Pleasantness and Power and Their Relation to Acoustic Key Features

Factor analysis of attributes describing various aspects of car sounds quality reliably shows that the emotional meaning and reinforcing properties of car interior sounds are mainly related to two categories: pleasantness and power. They form the four quadrants of an emotional space with one axis defined by “pleasant - unpleasant” and the other axis defined by “powerful - weak”. Application of these categories to a set of 51 car interior sounds reveals that no sound exists which combines a high amount of pleasantness with an equal amount of power. As a conclusion, a trade off between the technical realization of pleasantness and power is assumed (“trade off hypothesis of pleasantness and power”). It predicts that if the sound of a car is designed to be as pleasant as possible the impression of power might be strongly affected and vice versa. Thus, a compromise between these two effects cannot easily be realized. Analysis of the engine order level envelope (EOLE) of sounds typically representing the four quadrants show that pleasantness is associated with the height of the EOLE in the low frequency range. The impression of power seems to be related to the dynamic of the low frequency EOLE increase. Based on these observations an experiment is performed to pinpoint the trade off between pleasantness and power by manipulating systematically the interior sound of a selected car while driving. The experimental sounds are recorded with dummy head and scaled afterwards in the laboratory according to their pleasantness and power. The results confirm the prediction made by the trade off hypothesis as power can be increased to a certain extent without affecting pleasantness. If this trade off range is exceeded, pleasantness is reduced significantly.