Directional sound sources using real-time beamforming control

Quiet vehicles may be noticed relatively late and therefore constitute a potential risk for vulnerable road users such as pedestrians and bicyclists. The ideal acoustic warning signal generator notifies vulnerable road users while minimizing noise pollution. Several sensor systems exist which are able to reveal the position of the vulnerable road users, which information can be used by the warning signal generator. The warning signal generator is designed to generate the specified warning signal at the location of the vulnerable road user while the acoustic response at other locations is minimized. The directional sound beam was realized with an array of controlled actuators, using least-squares beamforming methods. The particular least-squares methods are based on measured transfer functions between the actuators and the acoustic sensors. Different actuator technologies were evaluated. Changes of the relative positions of the vehicle and the vulnerable road user require continuous adjustments of the sound beam. The latency of the beamforming method with respect to an adjusted beaming direction is an important factor for the present application. Different methods to generate the sound beam are described and advantages of the different beamforming methods in experimental results are shown. Rapid real-time adjustment of the beaming direction is demonstrated.