Hey engineering types, would this work?

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.

:scratch:

I basically understand how the doppler shift works, but is this kind of system really feasible?

S.

I am no genious, but I would think that this would only work if the sound from the exhaust was a constant, and not varied while it is being measured. Doubtful it would stand up as a ticket in court though.

Nothing will stand up in court until it's tested in front of a jury, appealed, etc...

I'll have to read the patent applications once they're published and see what I think.

Sure is. I would imagine that once the base note is isolated, the rate at which that note changes in pitch relative to the stationary observer platform could be used to determine velocity pretty easily.

Imagine what a car sounds like passing you at 60mph if you're standing still (more importantly imagine the rate at which the exhaust note changes in pitch - rising as the car approaches you, then falling as it recedes). Now, imagine the same thing, but the car is passing at 10mph instead - the rate at which the pitch rises and falls is much slower, due to the Doppler effect.

The biggest hurdle will probably be isolating the base note and filtering out extraneous sound. Time to add some variable pitch air horns to your car. :wink:

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Originally Posted by altiain

The biggest hurdle will probably be isolating the base note and filtering out extraneous sound. Time to add some variable pitch air horns to your car. :wink:

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Or eat a bunch of Beans! ::Fart::

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Originally Posted by POS Racing

Or eat a bunch of Beans! ::Fart::

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That's how my wife knows where I'm at...

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Originally Posted by POS Racing

Or eat a bunch of Beans!

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Sick and wrong.

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Originally Posted by altiain

Sure is. I would imagine that once the base note is isolated, the rate at which that note changes in pitch relative to the stationary observer platform could be used to determine velocity pretty easily.

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Is that assuming that the car's velocity remains constant? What if the driver is not using cruise and modulating the pedal?

Exactly... it works by the exhaust note being constant... what about during acceleration or deceleration? The exhaust note won't be constant. I wonder how far that will throw off the calculations.

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Originally Posted by Treibenschnell

Is that assuming that the car's velocity remains constant? What if the driver is not using cruise and modulating the pedal?

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I'm sure when the patent is published we'll see that they're measuring the doppler effect over about .01 seconds on either side of the measuring point... Not enough time for a lot of pitch change to occur due to throttle inputs.

I imagine it would be pretty easy to fight that... you could just be like "Yeah it recorded the guy next to me, I was in the center lane..." problem solved. It may be able to isolate one note, but who's note is it getting?

sure, its' certainly possible, but it's going to take a lot of development..

alo, the rate of the change is going to vary depending on which lane the car is in as well.. if the device is on teh shoulder, the pitch change over teh same period of time is going to be different for a car in the outside lane form the fast lane...

again, all things that they *could* overcome easy enough, but there's a lot that still has to be worked out there.

So what if you are driving a hybrid or fuel cell vehicle? :confused: :burnrubr:

Or someone could fashion a hybrid type deer whistle in order to create several tones coming from the same vehicle.

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Originally Posted by Bolix

I imagine it would be pretty easy to fight that... you could just be like "Yeah it recorded the guy next to me, I was in the center lane..." problem solved. It may be able to isolate one note, but who's note is it getting?

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Yeah, 'cause that excuse has worked sooooo well against radar and laser. :rolleyes:

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Originally Posted by tailchaser

Sick and wrong.

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Yea but think of the excuse you could use!

Officer Sparky : We clocked you with the new sound-a-doohickey doing 76 mph in a 55.

Me : No sir officer I just farted and I have the racing stripe to prove it! ::Clown:: You can smell my seat or just call in the CSI guys! ::Fart::

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Originally Posted by Treibenschnell

That's how my wife knows where I'm at...

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not the kind of BASS note i was thinking... :rolleyes:

i dont think this will hold. radar guns will catch the big rig next to you, even at a distance, and the officer will guess your speed. he can make it say whatever he pleases. this method wont work at a distance, where youre coming more perpendicular towards the machine, because it cant "hear" you from far away. if i see one of these coming, ima rev like crazy or step on the clutch. itll be 1000mph or just the sound of a dropping idle...

nope, untill i see it work. :burnrubr:

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Originally Posted by Treibenschnell

Or someone could fashion a hybrid type deer whistle in order to create several tones coming from the same vehicle.

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Did someone say Whistle Tips?! WOO WOO!!

Just shove a KaZoo in your tailpipe!

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Originally Posted by rx7gslse

Just shove a banana in your tailpipe!

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http://www.dnevkino.ru/films-foto/fi...yhillscop2.jpg
I'm not fallin for no banana in the tailpipe!

::Banana:: ::Banana:: ::Banana:: ::Banana:: ::Banana::

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Originally Posted by black roadster

http://www.dnevkino.ru/films-foto/fi...yhillscop2.jpg
I'm not fallin for no banana in the tailpipe!

::Banana:: ::Banana:: ::Banana:: ::Banana:: ::Banana::

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I just watched that a couple days ago... it made *me* feel old..