GMC Terrain noise canelling system

How can headphone technology increase a vehicle's fuel economy? Well, the truth is, it can't. Not directly, anyway. However, by employing an active noise cancelling system similar to what's used in some of today's high-tech headphones, General Motors solved a problem that would've otherwise plagued the GMC Terrain. In doing so, GM managed to squeeze another mile or two out of each gallon of gas put into the Terrain for an EPA rating of 32 miles per gallon highway.

GM engineers strapped a six-speed automatic to a 2.4-liter direct-injection four-cylinder engine and equipped the vehicle with an eco mode that lowers the transmission's shift points while improving the gas mileage. However, when eco mode was activated, the powertrain offered up an audible hum.

To counter the buzz, engineers installed an active noise canceling system that relies on two headliner-mounted microphones to detect the hum and a frequency generator that emits an "antinoise" signal through the vehicle's speakers to cancel out the engine's boom. And that's how headphone technology, in a roundabout kinda way, cranked up the Terrain's fuel efficiency.

[Source: GM via Autopia]