"Wow, what car is that?": Perception of exterior vehicle sound quality

Up until now most research and application in vehicle sound quality has been directed at describing interior vehicle sound quality. Even though the interior sound of a vehicle is a major component of the perceived sound quality, exterior sound is audible both to potential users and bystanders. It may be argued that interior vehicle sound quality is concerned with meeting the buyer's expectation, whereas exterior sound quality concerns a) attracting attention and positive responses of potential customers and b) minimizing negative responses in the general public. It may therefore be argued that optimizing exterior sound quality will benefit both consumers and the community. This article describes an approach to perceived exterior vehicle sound quality. To attain an understanding of exterior sound, we investigate both the semantic descriptions that are elicited when different exterior sounds are heard and specific situations (i.e. a given sound/vehicle in a given environment). Across different sounds and driving conditions we find four subjective dimensions: loudness/annoyance, perceived quality, low-frequency content, and temporal variations. This factor structure allows discriminating the sound quality of a variety of modern cars. In more specific tests we find that participants both discriminate between different vehicles and different environments (free field conditions, urban driving conditions as well as different street shapes). These results indicate that designing and predicting exterior sound quality is a multidimensional task that requires different approaches than those traditionally used for interior sound quality.