Annoyance, quality- and safety aspects of sound in truck cabins

Licentiate thesis, 2006

For heavy vehicles the interior sound environment is still more or less just a passive result of the engineering of the different parts that make up the vehicle, although measures are taken to keep sound pressure level within legislated boundaries. Additionally, the sound inside truck cabins is dominated by its low frequency (LF) content, and is hence prone to impair task performance and reduce wakefulness as well as cause general annoyance and different adverse health effects. In this report, four aims have been formulated in order to by use of a sound quality approach investigate possibilities to increase safety aspects of the sound environment, enhance positive and reduce negative subjective responses: • Understanding experience of and reaction to a sound environment such as the one in a truck cabin, with special focus on the prevailing high levels of low frequency content. • Understanding the relation between perceived negative and positive aspects of such a sound environment. • Investigate perceptually adequate ways of describing the sound environment, in addition to the for this context inferior traditional methods such as A-weighted sound pressure levels. • Investigate influence from physical properties of the sound environment, compared to influence from the information that is conveyed by the sound. Three dimensions were found to be of great importance for the assessment of interior truck sound: Annoyance, Quality and Wakefulness. Additionally it was found that reducing some negative aspects along the annoyance dimension also reduced some positive aspects along the quality dimension, indicating the need for a careful optimization between these dimensions. Importance of high frequency content for perception of differences in the low frequency region showed the use of spectral balance as a descriptor of interior heavy vehicle sound. Also, information content showed to mediate annoyance and affective responses to interior truck sound.