Half a croissant, on a plate, with a sign in front of it saying '50c'
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Ventriloquist Horn

To get pedestrians to jump out of the way well in advance
  [vote for,

The roads in my part of the world are narrow, crowded and filled with people whose one mission in life seems to be to make life miserable for drivers. They only give way when you are about to run them over - and if one gets confused and jumps the wrong way, you have to be quick on the brakes. Come to think of that, that is how I walk, too. No footpath.

Enter the ventriloquist horn. Using advanced wave shaping technology and an array of piezoelectric speakers (paint on speakers - link) the horn is made to sound as if coming from a point just behind the victim, who then skedaddles off the way pronto.

The entire frontal area of the car, except the glass, is a giant array of piezoelectric ultrasonic transducers. They are driven with controlled phase such that the ultrasonic energy concentrates to a spot some three car lengths in front of the car. The ultrasound is modulated with a pulse rate appropriate to the pitch of the car horn.

The concentrated ultrasound heats the air which expands and produces sound according to the modulation. Since this virtual horn moves through the air with the motion of the vehicle, it seems to an unwary pedestrian that he is about to be run over - when you are, in fact, a comfortable distance away.

neelandan, Jan 15 2003

Paint on Speakers http://www.halfbake...int_20on_20speakers
Cover the front of the car with this. [neelandan, Oct 04 2004]

Ultrasonic Interference Loudspeaker http://www.atcsd.com/pdf/HSSdatasheet.pdf
Ventriloquist's voice thrower that works! [csea, Oct 04 2004, last modified Oct 21 2004]

Illustration (from web archive) http://web.archive.....com/it2n/horn.html
A pictorial representation - Original artwork by Bristolz [neelandan, Dec 21 2013]


       Croissant for the elegant prose and picture.   

       Maybe I'm a little dim. I'm having trouble with the ultrasonic bit....   

       I think a Ventriloquist Horn is possible, using phase modulation, like Surround Sound. A doppler shift could be mimicked to give the impression of movement. Even so, it'd only be possible to spoof a brief blast from a car passing to the side.   

       Great idea, though.
FloridaManatee, Jan 15 2003

       Awesome picture! I think we need special pink croissants for people who earn praise primarily for their awesome artwork.
phundug, Apr 16 2003

       Don't know about paint-on speakers, but the ultrasonic interference loudspeaker technique is baked, and works quite well, throwing a 3 degree beam where pointed. Should it focus on a pedestrian, the effect is similar to wearing headphones (!)   

       See link.
csea, Mar 03 2004


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