leftlanenews.com — 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. It works by detecting the Doppler shift from the sound of the car's exhaust as it passes. Brilliant yet horrible all at the same time!
Apr 27, 2006 View in Crawl 4
mordredApr 27, 2006
What if I'm "speeding" in an electric car with no sound from the exhaust?
cykaosApr 27, 2006
Read the other comments. It doesn't measure distinct sounds but the change in pitch of the sound.. You could measure the pitch change of a kid screaming or a horn honking, or car exhaust. The change in pitch is relative to the velocity. So like everyone has said, as long as the sound is constant you can figure out the speed from the change in pitch.
d03boy_Apr 28, 2006
Yay, now we can (easily) find a way to get around this "technology" using noise cancellation techniques.
eyegorApr 28, 2006
The way the system works is that it listens to the exhaust tone as the car approachs (with up doppler) and when the car is at its closest point of approach (directly over the microphone) the exhaust tone is at its fundemental frequency. As the car moves away, the dopper effect is again seen with a similar downward shift in the frequency.If the car upshifts or downshifts while near the microphone, then the tone will change and affect the reading. That being said, you probably only need 25 - 50 feet on either side of the microphone to gather all of the info you'll need. Not a lot of time to be able to change engine speed.Since they're only measuring the delta between the shifted freq(s) and the fundamental tones, it doesn't really matter too much about glass packs, rpms, etc. The only thing that matters is that the source freq doesn't change while passing over the mike and that no other car interferes with the reading.I
datastorageguyMay 1, 2006
Correct me if I am wrong here but...isnt radar doing the same thing?
freeipodguy_comMay 4, 2006
camiller, it is your concern only as long as you don't use the information to endanger the lives of others. If you are speeding, you are endangering the lives of others. Who do you think you are?