Car Interior Sound Quality: Experimental Analysis by Synthesis

Car interior sound quality (CISQ) can be described by two perceptual factors forming a four quadrant scheme of sound quality with one axis defined by "pleasant–unpleasant" and the other axis defined by "powerful–weak". Within that scheme individual sound events are found to be located relative to their degree of pleasantness and powerfulness. Scattering of a representative sample of car interior sounds within the scheme reveals that if the sound of a car is designed to be as pleasant as possible the impression of powerfulness might be strongly affected and vice versa. Thus, a trade-off between these two effects might be realizable only in a limited way.

An experiment was set up to prove whether this trade-off can be pinpointed more precisely in an analysis by synthesis approach. The engine order level envelope (EOLE) of sounds representing a broad spectrum of sound quality show that pleasantness is associated with the height of the EOLE in the low frequency range. The impression of powerfulness seems to be related to the change of the low frequency EOLE. To test the validity of these observations the interior sound of an experimental car was manipulated with an on-line sound simulator. The sounds thus produced were recorded with dummy head and scaled by subjects. The results confirm the prediction made by the trade-off hypothesis as powerfulness can be increased only to a certain extent without affecting pleasantness. If the trade-off range is exceeded, however, pleasantness is reduced significantly.