The effect of listener head orientation on front-to-rear speech intelligibility in an automotive cabin

Abstract

The listener head orientation significantly affects speech intelligibility (SI) in the small acoustic space of an automobile, owing to near-field binaural listening and special acoustic conditions such as early reflections and seat-back occlusions. However, situations involving a back-row listener and a front-row speaker (i.e., front-to-rear scenarios) have not yet been studied. Such scenarios are dominated by non-uniform early reflections rather than direct sounds, making them distinct from cases considered in previous studies. This study investigates the effect of listener head orientation on SI in front-to-rear scenarios in an automobile, using both the speech transmission index (STI) and subjective experiments. A virtual speaker (i.e., a loudspeaker) is located in the driver’s seat and faces forward. Binaural room impulse responses are measured on a dummy head in the three rear-row seats with different head orientations. Using the binaural room impulse responses, the corresponding STIs are calculated, and the Chinese SI scores are measured virtually via headphones. The results show that the SI variation range for various listener head orientations in front-to-rear scenarios is greatly reduced compared with that in the rear-to-front scenarios considered in previous studies. Overall, the effect of listener head orientation on SI is mostly negligible when a listener in the rear row listens to a speaker in the front, with variations in the SI score of no more than 5%. The present study provides a supplement to previous studies and helps to deepen understanding of the effect of multiple factors on SI in an automotive cabin.