There is an increasing need for personal audio systems, where two people are listening to different audio channels in adjacent seats in an aircraft or road vehicle, and each person wants to hear their own channel faithfully reproduced, with a minimum of interference from the other person channel. In this work, two methods of enhancing this acoustic isolation for sound reproduction with headrest loudspeakers were discussed, initially using a simply free-field model, and representing after a more realistic situation with a finite element software (ANSYS). The first method proposed used feedforward control between the two seats and the second control strategy employed an optimised nearfield acoustic array to reproduce the signals close to the array, but to attenuate the signals in the adjacent seat. Numerical simulations were carried out for the design of such an array maximising the ratio of the mean square pressures in the zone where sound is to be reproduced (bright zone) and the zone where sound is to be attenuated (dark zone). The simulations suggested that active control works well at low frequencies (below about 500Hz) but the zone of quiet becomes there rather small, whereas the nearfield array gives good isolation up to several kilohertz. These predictions were then investigated experimentally using a pair of thin loudspeakers mounted face to face in one side of the headrest. Informal listening tests indicated that the reduction in crosstalk between the seats was impressive, that the residual sound was less intrusive, and that the subjective impression was maintained even for significant head movements.
 |
 |
| Listeners in adjacent seats are listening to different audio channels radiated by loudspeakers in the seat headrest and corresponding pressure level generated by two monopole sources whose source strength is adjusted to maximise the contrast between the mean square pressure in the bright zone and the dark zone | |
