In seeking ways to counter rising fuel prices and lessen environmental impacts, the auto industry is staking out two key trajectories. One is the industry's commitment to lightweight design. The new VW Golf, for instance, weighs in at over 100 kg lighter than its predecessor. The other is the trend toward hybrid and electric vehicles that can complete at least part of a journey solely on electric power.
What both developments have in common is the challenge they present for vehicle noise optimization. The lower the vehicle’s target weight is, the less material can be installed to reduce noise, meaning that noise penetrates the vehicle interior (and passenger ears) unmitigated. Electric motor-powered vehicles, on the other hand, by their very nature emit little or no noise at all. As a result, pedestrians are unable to hear an electric vehicle until it is virtually upon them – or worse still, they fail to hear the car at all. Moreover, the lack of engine sound exacerbates the impact of other vehicle noise, meaning that road or wind noise, or wind may be perceived as relatively loud in the vehicle interior.
To counteract these effects, auto manufacturers need effective systems which can synthesize sound in electric vehicles to warn pedestrians, and that can also suppress interior noise successfully. A solution that excels at both, external sound synthesis and internal noise suppression, is HALOsonic, a joint development of HARMAN and the British developer Lotus Engineering.
Fig.1: Complete audio synthesis and noice cancellation system in a car
Protection through sound
The acoustic pedestrian safety feature in HALOsonic works according to a relatively simple principle. A loudspeaker is mounted to the front of the vehicle. This has the effect of projecting sound forward to the front of the car. The audio source is supplied with signals that correspond to the driving situation, ensuring that the synthesized sound is consistent with the vehicle's speed and acceleration.