2011 GMC Terrain
GMC has introduced a new system that utilizes the stereo to aid the GMC Terrain in achieving higher gas mileage. While fuel economy and audio systems do not have any significant direct connection, GMC is cleverly utilizing technology to make the Terrain a viable competitor while making it more efficient.
Terrain drivers can select an "Eco" mode that programs the six-speed automatic transmission to choose lower shift points. This allows the vehicle's standard 2.4-liter 182 hp engine to run in at lower rpms when desired.
The low gearing gives the Terrain a 22/32 city/highway EPA fuel economy rating. GMC points out that this "tops" the 28 highway mpg achieved by the Honda CR-V, Toyota RAV4 and Ford Escape (all of them, including the Terrain get 21-22 mpg city ratings.) At a base price of $24,250, the GMC Terrain also starts out a few thousand dollars more than the competition it named. GMC can likely justify some of this extra cost with a high list of standard features.
The downside of this extra fuel economy is that the low gearing also creates what GMC calls, "An objectionable low-end frequency boom." This is unacceptable in a car that cost more than the competition, so GMC utilizes the car's speakers to combat the sound problem.
The GMC Terrain borrows similar technology used in noise-canceling headphones to make sure the occupants do not experience any of the low-end grunt from the drivetrain. Considering that this active noise cancellation technology can not only reduce or eliminate the low-end engine noise, but also other mechanical noises, it will likely make an appearance on other General Motors vehicles. "The use of active noise cancellation for fuel economy benefit on Terrain is among the first at GM," said Paul Beaker, program engineering manager for GMC Terrain. "It has strong potential for implementation on other four-cylinder vehicle programs."
For those who don't remember their high school science classes, the noise active cancellation system is a lesson in applied physics. All noise is produced in a wave pattern. By creating a wave of the exact opposite amplitude, it cancels out the original sound wave. The system in the GMC Terrain recognizes the wavelengths of the offending noise using microphones in the interior headliner, and then the vehicle's speakers produce counteracting waves. The two sounds cancel each other out so the occupants do not hear the engine noise or the artificial noise created by the speakers.
So really the radio system is not actually helping the vehicle save any fuel. Instead the Terrain's speakers are just making the gas saving mechanisms tolerable for occupants.