New Scientist
magazine reports that researchers at the University of Tennessee and Batelle Institute have applied for patents on a
system that detects the speed of a passing vehicle based on its exhaust note.The system uses microphones to capture the sound of a passing car, and then filters out all but the sound made by the engine. By measuring the doppler shift of the engine sound as it moves past the speed trap, the system can calculate the vehicle's speed.
While the sound detector is unobtrusive and completely passive (therefore undetectable by a conventional radar/laser detector), identifying speeders will require something a little less stealthy, like a traffic camera. Of course, other early detection systems are possible, like the subtle warning in the accompanying picture.
Hmmm. Sounds like better muffler technology is in order.
[Source: New Scientist]
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Reader Comments (Page 1 of 2)
Ryan @ Apr 27th 2006 12:11PM
ekkk, I scared!
nick @ Apr 27th 2006 12:22PM
even if you have a completely silent drivetrain, the car still makes noises. like tires on the road surface and the air as it parts around the car. you could just as easilly filter on those sounds and measure the doppler shift in them.
solution, 115dB freight train airhorn. audio recording systems can't filter a heck of a whole lot when they are saturated by 115dB of shorts soiling sound. "sorry officer, i went fot the cruise control and hit the horn"
Alex @ Apr 27th 2006 12:25PM
This is crap, what about performance exhausts? Am I going to get a $500 ticket because they think i'm going a bazillion miles an hour? doubtful, there are plenty of noises that will obstruct such a device, especially in the ny metro area
Tom @ Apr 27th 2006 12:43PM
Engine noise? Won't this be inaccurate if the driver is accelerating or decelerating? The noise is only constant if the engine is at constant revs.
Mauwk @ Apr 27th 2006 12:46PM
I got a great idea. How about we admit that selective speed enforcement does nothing more than generate revenues for corrupt local governments?
Scott @ Apr 27th 2006 12:54PM
Yeah, I guess it would work; but all the driver would need to do is slow down before he passes the trap. Doesn't seem to be too effective to me. And without an officer there, it would seem fairly easy to me to contest this in court.
Dave @ Apr 27th 2006 12:59PM
Perhaps you could put a highly directional speaker in the back on your car. You could then produce a warble tone at or around the frequencies they are using. This would mask the Doppler effect of your engine.
eyad @ Apr 27th 2006 1:00PM
explain to me how they can target YOU specifically on a highway unless there was no other car nearby.
also, another reason to get a hybrid which can shut down the internal combustion engine at speed (or by user input).
chris @ Apr 27th 2006 1:36PM
what about tuner cars. most exhaust notes are higher than normal cars?
Tim UF @ Apr 27th 2006 2:05PM
just learn how to rev the throtte as you pass... itll counteract the doppler effect (apparent frequency decreases as outbound velocity goes up, so, just rev it to boost the freq!)... if its listening to exhaust note.
Howard Kerr @ Apr 27th 2006 3:14PM
I read many years ago that Lotus was working on a system to "drown-out" noises that cars make in a bid to make a quiet car without having to load it down with sound-deadening. I think I also read recently, that Ferrari was using a similar system on it's newest cars as a means of passing Europe's tough noise pollution laws. In both cases you would "flip a switch" and the sound(s) the car/exhaust was making would be changed to a nearly inaudible pitch because a sound or sound spectrum would be produced that cancelled out unwanted/unpleasant noise. It sounds (no pun intended) like this technology could "fool" this new system IF a way could be found to broadcast it outside your car.
bernie @ Apr 27th 2006 3:33PM
That's baloney. How does it know what gear you're in, drive ratio, tire size, and the dozen other variables to vehicle performance? What a crock of BS.
risingsun @ Apr 27th 2006 3:36PM
I don't see this actually making it into the hands of your local law enforcement. Just like the exhaust noise level laws when NO officer has a dB meter, and it depends on how close you are.
If an officer claims to have used radar or laser to acquire your speed, ask the officer if they are certified to use the equipment. Most motorcycle officers are, but not as many patrol car officers are.
Even when I really AM speeding, it seems that the officer always says I was going several more miles per hour than I really was... kind of fishy.
risingsun @ Apr 27th 2006 3:39PM
And selective speed enforcement IS just a cash flow scheme. There is too much profiling by police for it to be fair. I get pulled over almost weekly, and I DON'T SPEED. Just because I'm driving a black Honda with dark tint and I'm 22. Just like airport screenings... those are random... riiiiight. My hispanic friend that flies back and forth to college gets "randomly" searched every time.
Micah @ Apr 27th 2006 3:50PM
What about hybrids? When operating on the electric motors do they produce any noise from the tailpipes?
Eddiecoaster @ Apr 27th 2006 5:30PM
RE: 11...
I dont know so much about targeting a certain age group or a certain car. I have a Acura rsx, silver, with (loud) exhaust, a wing, and a very visible radar detector in the front wind shield. I *knock on wood* have yet to be pulled over, and i have been driving it since last aug. By the way, im 17.
Perhaps it's a town by town thing, though.
Justin Bell @ Apr 28th 2006 3:44AM
There are some real idiots here that either don't understand science, or don't read beyond the headline. This doesn't measure the pitch or loudness of the exaust, but the doppler shift, which basicly is the change of pitch over time.
As for trying to fool it by accellerating at the right time, I'm not sure if that would work or not. Depends how sophisticated the software is, I guess.
Road Tester @ Apr 28th 2006 6:50AM
A system similar to this is already used in TV broadcasts, when the revs are shown. So far I'd thought the sensor needed to be attached directly to the car, though. Like many others here, I question its feasibility in road traffic, with several cars approaching the sensor.
catching violators @ Apr 28th 2006 11:06AM
This is nothing new. I looked at this 9 yrs ago as a way of verifying that certain racing teams weren't violating a rev limiter rule. Not only could you pick out the RPM but also the speed of the car...provided your measurement wasn't contaminated by too much background noise. It's amazing what you can learn about a car based on its raidated noise.
MikeW @ Apr 28th 2006 1:40PM
Even without the engine running, there is still a general doppler shift noise from the tires, car aero wake.
Time for front mounted exhausts. Isn't VW working a car with a transverse front-mid engine with the engine right on the firewall, so the pedestrian safety is improved for EU rules. Why bother routing the exhaust to the back, when mufflers can make good crumple zones (see McLaren F1-rear muffler crupple zone)