Tuesday 25th April 2006

Can they catch you using sound?

Acoustics developed as sneaky speeding deterrent

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Just watch for microphones

The next technology under development to catch you speeding is based on sound. According to New Scientist magazine, a system developed by the University of Tennessee and the Battelle Institute uses microphones hidden in the road verge to capture the sound of passing cars.

There's no radiation, radar or other telltale sign that there's a detector there, which might defeat the point of having detectors -- but that's another issue. It's what happens after the sound has been capture that's intriguing.

Captured sound is digitally filtered to remove background noise and then, according to the report, software can calculate the speed of the vehicle by the sound of its engine. It uses knowledge about the type of engine, the angle and type of road at the capture point, and the Doppler shift as the car passed by.

It can measure engine speed by detecting firing pulses and comparing the noise with a library of acoustic signatures. This allows it to estimate the size of engine, we're told. How it'll cope when most vehicles use just a handful of engines -- a point we're rapidly approaching -- isn't known.

It's been tested too, by recording vehicles travelling at known speeds and comparing results. The system measured the correct speed within a few percentage points in 32 out of 33 instances.

Developed with funding from the US Department of Energy, the system has been patented.

Scary or what?

[pdV6]

The atricle said:

It uses knowledge about the type of engine

And how, exactly, would it know that?

[dinkel]

So pasing the mike in low gear gets you fined, choose a high gear (and some extra secs to reach your speed) and it's allright?

[Yugguy]

Sounds like a load of arse to me. I could be doing 30 but in first gear with my engine racing and it'd sound like I was doing 90.

[ripton]

Yugguy said:

Sounds like a load of arse to me. I could be doing 30 but in first gear with my engine racing and it'd sound like I was doing 90.

You'd expect that the boffins developing this would have slightly more grey matter - the engine note is used for identification of a vehicles passing a number of sensors and claculating speed through time over a known distance. You might get away by rapidly changing gear

[Sonic Nonsense]

Yugguy said:

Sounds like a load of arse to me. I could be doing 30 but in first gear with my engine racing and it'd sound like I was doing 90.

By the degree of Doppler shift (how much the engine noise is distorted as it passes the mic) would be greater the higher the speed, so changing gear probably wouldn't save you.

Dunno about you, but suddenly electric cars are looking more attractive!


Edit to correct sucky spelling

>> Edited by Sonic Nonsense on Tuesday 25th April 11:07

[gizard]

pdV6 said:

The atricle said: It uses knowledge about the type of engine And how, exactly, would it know that?

Plus if you have after market changes - i.e. exhaust etc. or even a hole in the exhaust

HAHAHAHAHHA - just though - what about an electric car!

[BliarOut]

gizard said:

pdV6 said: The atricle said: It uses knowledge about the type of engine And how, exactly, would it know that? Plus if you have after market changes - i.e. exhaust etc. or even a hole in the exhaust HAHAHAHAHHA - just though - what about an electric car!

Or wheels with a different rolling radius to standard...

[turbobloke]

They're quackers, and it's a dead duck.

[Yugguy]

You could make yourself a very clever system that would analyse the sounds your car produced and then transmit its own sounds to cancel them out.

[turbobloke]

Yugguy said:

You could make yourself a very clever system that would analyse the sounds your car produced and then transmit its own sounds to cancel them out.

Don't M-Benz already use anti-sound?

[dinkel]

Sonic Nonsense said:

Dunno about you, but suddenly electric cars are looking more attractive!

Automatic, Variomatic . . .

[7db]

Or you could run the microphone over...

[chrisjl]

It's not about what gear you're in, or what circumference your tyres are. It's about the difference in the perceived sound as you go from approaching the vicinity of the microphone to departing it.
I'm not sure what purpose identifying engine size has (or do they mean number of cylinders?).

[Sonic Nonsense]

And what about Chav-boys whose stereo's (or ICE or whatever the young whipper-snappers call it these days) are loud enough to drown out an Iron Maiden concert, let alone the sound of their engines... That'd have to be some kick-ass noise cancelling software!

[eein]

I can see how this would technically work, but I'd be surprised if it could be made commercially viable compared to other technology for speed detection. Averaging camera systems do not emit anything either and could, if required, be made very small and concealed somewhere.

With the sound, I would have thought it would be easier to do if they had two mics spaced apart using signal processing techniques a bit like array antenas use.

[r988]

eein said:

I can see how this would technically work, but I'd be surprised if it could be made commercially viable compared to other technology for speed detection. Averaging camera systems do not emit anything either and could, if required, be made very small and concealed somewhere. With the sound, I would have thought it would be easier to do if they had two mics spaced apart using signal processing techniques a bit like array antenas use.

Would have thought the myriad of current speed dectection systems are vastly superior and more accurate, this is like reinventing the wheel but making it an octogon shape.

[cooperman]

I thought they used this to detect submarines and called it SONAR. It's a 70+-year-old technology.

[Einion Yrth]

cooperman said:

I thought they used this to detect submarines and called it SONAR. It's a 70+-year-old technology.

Sonar is active, this is passive.

[leosayer]

chrisjl said:

It's not about what gear you're in, or what circumference your tyres are. It's about the difference in the perceived sound as you go from approaching the vicinity of the microphone to departing it.

Reminds me of a 2 Ronnies sketch where they're driving an old police car, ringing one bell as the approach a pedestrian and then changing to a different (deeper sounding) bell as they drive past. Very funny.

[dean_ratpac]

just hope the flames out the back set the mic's alight!