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The paper describes the development of a scale for the assessment of car interior sound quality. The scale had to meet three demands: Standardization, i.e. the scale values of different sound events should be directly comparable to each other. Economy; i.e. the use of the scale should be time efficient. Validity, i.e. the scale should be suitable for a precise distinction between sounds of different quality. A rating scale based on centile standards was constructed enabling the economic and specific measurement of four basic qualities: pleasantness, power, brightness and impulsiveness. In a series of experiments the scale was applied to a representative sample of interior sounds. The results show that the scale differentiates indeed precisely between the individual vehicles. This gives a reliable data base for the selection of reference sounds for optimization purposes.

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.