"" from LL News.

A new type of speed trap developed by the University of Tennessee,
can detect the speed of a car based on the sound of its exhaust as it passes.

According to a report in the 2548 issue of New Scientist,
the system uses microphones to record the sound of passing cars.
A computer then program isolates the various vehicles.

The program calculates the vehicle�s speed by measuring the exhaust sound�s Doppler shift.
According to patent filings, development was funded by the US Department of Energy.

Unlike radar systems that can be detected by dashboard-mounted devices,
this sound-based system would be undetectable.

 

I don't see how that is possible. Considering all the different types of exahusts on cars these days. Hell a Yugo with a hole in the muffler will sound super loud, even though its going 10 miles an hour.

 

The speed isnt detected from the volume so it wouldnt matter how loud your exhaust is. It only uses the exhaust sound as a signature to pick your car out from all the other cars, and then it tracks that sound as it passes the microphone.....the ammount of dopler shift in the sound will let the sensor figure out how fast you are going. At least, thats how I imagine it'd work....

 

You just need a quiet exhaust! (aka a turbo!)

Or just you wait - I'm sure someone will come up with audio interference to render the system useless...

 

It would be quite simple to defeat actually. Since it is using the doppler affect and assumes you are traveling a constant speed. You just need to source a sound by the car that wildly varies in pitch over a short period of time. The machine will think your speed is all over the place and be unable to 'lock on' accurately.

JH

 

Ya ill go 25mph on first gear and it sounds the same as going 150 mph on 6th gear.

I dont think that is possible.

 

It has nothing to do with how fast your engine is going. 9000rpms in 1st gear in an S2000 or 800rpms in a diesel truck, it doesn't matter.

 

I seriously didnt get what u were trying to say.

Faster ur engine RPM higher the sound vibration. is that right or no?

 

The doppler shift is based on the frequency change for any sound. When you are approaching the trap, the exhaust sound is a higher frequency because your speed is added to the frequency of the sound emitted by your car. When you are driving away, the sound is a lower frequency. Think of the sound a siren makes coming toward you then moving away from you. The sound has a higher pitch coming towards you and a lower pitch moving away.

 

no way....... what about aftermarket and oem.... how will they know?

 

Race car around a track is a better analogy than a siren

 

How they pick your car out of the rest of the cars in a pack could be difficult. If there is a couple feet of space between you and the next car, it could be easy. I haven't read the patent or article but it seems they would need to have a video or camera system to actually pick your car out of a pack or an RFID tag system. I don't want to start a big brother thread, but a RFID chip with a unique serial number in every car would cost less than $0.25 per car, an RFID chip detector attached to the sound/speed unit would cost less than $100 per unit and a national database matching RFID serial numbers to VIN numbers would be trivial. Hopefully big brother is worried about other things besides chronic speeders. If not, I'm selling my G and buying a Prius.

 

Current Radar uses the doppler effect now! Radar picks up the change in returned wave frequency that results from the doppler effect. This is pretty unlikely stuff and sound like step back technolgy wise when laser is nearly unstoppable.

 

This would require two measurements of sound frequency, one heading toward the unit and one heading away after you pass it. Simple answer... I shifted gears officer. End of discussion.

Curt