The object of this investigation was to determine whether it would be possible to use loudspeakers located in the drivers headrest to produce driver information messages at a sufficient level for the driver to hear them without disturbing their passengers. The messages were of 4 types; (a) of those giving route guidance ; (b) those giving advice about traffic conditions, and suggesting that the driver either changed route or slowed down; (c) those concerned with the condition of the vehicle (tyre pressures, brakes etc); and (d) those concerned with weather conditions. A total of 22 messages were read in a normal voice and recorded on a tape recorder fitted with volume control. The optimum sound level for the messages was obtained by using a panel of 16 drivers aged between 20 and 59 years. Each member of the panel was asked to drive the test vehicle around a circular track at 60 km/hr, as the messages were played back to him at various volumes. Passengers were asked to comment on the disturbance caused by the messages. It was found that the optimum sound level varied between age groups, but that the level which suited all groups was 65 dB(A). Most of the passengers could hear that announcements were being made without being able to understand them. Half of the passengers thought they should be able to hear them too anyway.
Samenvatting