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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]


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  • 16 Comments
      • 3 Years Ago
      This is kinda of like masking a odor, the original unwanted odor is still there but the occupants of the effected vehicle get overwhelmed with the new chemical fresh lemony odor which is more acceptable. The original sound is still there, it is turned into a more pleasant sound with added sound waves.

      Eliminate it at the source, vehicles have got to many gadgets like this to trouble shoot.
        • 3 Years Ago
        " vehicles have got to many gadgets like this to trouble shoot."

        +1
        What happened to KISS? Or, if saving gas is really that important to someone, quit driving like a jerk. Wow, you mean the vehicle operator has the power to effect increased mpg?
        • 3 Years Ago
        Not quite MikeY but close. When you do an active noise control system in this arrangement, you minimize the offending sound at the error microphone. Notice how the error cancelling mic is near the head? The unwanted side effect is that there are other points in the sound field that can actually be louder. Luckily the speaker system in a car is usually optimized to present excellent sound to the head spaces of the occupants. I wonder what happens in this arrangement for the non-optimal location (read that as any spot other than the Driver)?

        I suspect the iphones system is like a lot of other phone, a directional microphone and a filter set that is keyed into the normal speech range.
        • 3 Years Ago
        Except it is more like filtering than masking. As far as the occupants are concerned, there is _no_ noise, at least in theory.

        I'm a bit concerned about the effectiveness of this approach, though. The noise in the car is not only the one "radiated" one but also (perhaps primarily) the noise "conducted" through the car body. I don't think that this two point noise cancellation will make the latter go away.
        • 3 Years Ago
        It's a very inelegant solution.
        • 3 Years Ago
        EVsuperhero; you nailed it.

        Lipstick on a pig.. how about they fix the booming sound that this motor/transmission is making in the first place?

        It is probably due to the fact that the transmission lugs the hell out of this motor by design to stretch the MPG.
        And the fact that DI motors sound kinda diesel-esque due to the high pressure fuel injection
        • 3 Years Ago
        As nbs said, not quite masking. I just want to add that masking would be cranking up your favorite tunes so you won't hear anything else. Noise canceling actually creates "mirror image" sound waves that neutralize the sound waves you don't want. That noise actually disappears. This tech is not only in headphones, but is also on the iPhone 4 -- background noise is negated so all the other party hears is your voice.
        • 3 Years Ago
        I could deal with a hum, but why does this car hum in eco mode? whats humming? It's nice that it's masked, but why is the terrain the only car that hums in eco mode?
      • 3 Years Ago
      This phase cancelation scheme isn't exactly knew. It's already being used in a number of commercial vehicles. Perhaps it can help the Fisker Karma with it's Sport mode.
        • 3 Years Ago
        I'll take one of those Karma mufflers for my 2.0L i4 car.

        It'll sound like a v8 then, right?
        • 3 Years Ago
        Two wheeled menace

        Perhaps you're thinking of the Karma's external audio device, which could potentially make any sound you'd like. There are already aftermarket kits that can accomplish this, if you're looking to retrofit your vehicle.

        The muffler is intended to reduce the noise of the engine, not make it sound like something else. Other reviews by those who were at the same test drive mention that the Karma's exhaust sounds like a Pontiac Solstice GXP - not surprising, since it's the same engine. Likewise, it isn't the worst sound to make, but perhaps not what you would expect from a full-size luxury sedan, hence the decision to upgrade the muffler.

        "When battery propelled, the car sounds eerily like a taxiing jet — absolutely fascinating. Unfortunately, when the Ecotec engine chimes in — its exhaust hoarsely huffing from orifices just aft of the front wheels — you look around wondering where the Pontiac Solstice GXP is. When I mentioned this to the engineers they rolled their eyes and replied that a new exhaust is on the way. In a delightful irony, the Karma’s EV operation can be too quiet for unsuspecting pedestrians, so it emits an artificial but cool, future-world sound from both the car’s nose, and what appears to be dual exhausts at the rear. Go figure."

        http://www.motortrend.com/roadtests/alternative/1102_2012_fisker_karma_drive/engine.html#12987550292711&DISPLAYINTERSTITIAL_15

        Car and Driver actually seemed to like the exhaust note:

        "Tugging the “sport” paddle to the left of the steering wheel brings additional energy to bear. When the gasoline engine kicks in to supplement the battery pack’s wattage—to trim the 0-to-60-mph run from a claimed 7.9 seconds to 5.9, or to add 250 miles to the driving range—the extra thrust is accompanied by the whistle of a turbo spooling up, the snarl of angry exhaust gas, and a resonant boom or two. Bent on fulfilling its mission, the generator set keeps growling even when you ease off the accelerator."
        • 3 Years Ago
        Exactly what I was thinking. Hopefully a new muffler will be the fix the Karma needs, but I certainly expect to see this sort of sound manipulation to become quite commonplace, considering how cheap it is to implement.
        • 3 Years Ago
        Sorry for the typos. By "knew" I meant "new" and by "commercial" I meant "consumer".
        Any video reviews of the Karma out? I'd like to have an idea of how bad the Sport noise is.
      • 3 Years Ago
      Good job GM!!! Now may be you can save on sound proofing materail too...I like to see noise cancelling in all the car, it's worth it.
        • 3 Years Ago
        I think this is the point. Body boom is controlled by upgauging the sheetmetal or with a lot of heavy sound package items like mastic. That's how they make the fuel efficiency improvement...lower weight.
      • 1 Year Ago
      have just purchased my 2nd terrian, a 2013 slt 4cyl awd , have a noise on differnt road surfaces that sounds like a person talking in an emty room, dealer has called gm and was told that this the nature of the beast? this is not a good or even close to a good answer. are me &my wife the only people that here this sound in their terrians?
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