Case Study: Experimental Study on Enhancing Acoustic Contrast of Personal Sound Zones in a Car Using Headrest Loudspeakers

Personal sound zones (PSZs) in cars allow occupants in different seats to enjoy distinct audio content without mutual interference. However, achieving sufficient acoustic isolation in real-world vehicle cabins remains challenging. In-vehicle experiments were conducted to enhance acoustic contrast using four headrest loudspeakers mounted on the rear-right seat to create dark zones at the front seats. Three arrangements of four headrest loudspeakers on a single seat were evaluated: longitudinal horizontal, lateral horizontal and vertical configurations. Compared with distributing four headrest loudspeakers across two seats, concentrating them on one seat yielded better acoustic contrast. When evaluated in the car using control points distributed on a horizontal plane, the vertical configuration exhibited superior performance among the tested arrangements, achieving an overall acoustic contrast of 12.4 dB over the 88–4525 Hz frequency band. This represents improvements of 3.9 dB over the two-loudspeaker setup and 0.9 dB over the two-seat-distributed four-loudspeaker arrangement. These results indicate that the vertical loudspeaker arrays on a single seat provide an effective approach for improving PSZ isolation in automotive environments. However, this enhanced acoustic isolation comes at the cost of increased array effort at low frequencies compared to the two-seat distributed configuration, as quantified in the study.