By on February 27, 2011

A GM NVH engineer brags:

[GMC] Terrain measured quieter than the Honda CR-V and Toyota RAV4 in our on-road interior noise tests. At 70 miles per hour, Terrain’s interior is quiet enough to allow conversation in normal tones of voice.

How did they manage that? Hours of engine tuning, right? Wrong.

When GM engineers set out to deliver segment-leading fuel economy on Terrain they chose to lower the 6-speed transmission’s gear shift points to enable the Ecotec 2.4L four-cylinder engine to run at lower rpm torque. In this “Eco” mode, which the driver can activate with a click of a button on the console, the torque converter clutch engages at lower engine speeds to help save gas. While the engineering action improved fuel efficiency by up to one mpg, it also created an objectionable low-end frequency boom. To counteract that boom the engineers turned to active noise cancellation technology.

Terrain’s noise cancellation system relies on two microphones embedded in the headliner to detect the hum and prompt an onboard frequency generator to create counteracting sound waves through the audio system’s speakers and sub-woofer. The system also reduces higher rpm engine noise at highway cruising speeds to help keep the vehicle interior quiet.

OK, that solution may not satisfy our desire to imagine engineers slaving over the details of engine tuning, but hey, it’s a solution. Too bad GM’s Theta CUVs have yet to live up to their MPG ratings in real-world testing.

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31 Comments on “How Do You Keep Fuel Economy Quiet?...”

  • avatar

    I can’t believe its taken this long for a manufacture to use this technique to quiet a cabin of a vehicle.  How long has this technology existed?  At least 20 years.
    I remember having a conversation with my car pool buddy about this a few years ago, but I was thinking more along the lines of using phase opposite frequencies to reduce vibration in the chassis to keep a vehicle in new condition longer, as well as quieter.   Although, that would probably use quite a bit more energy than just quieting an interior.
    An issue I see is this being used a shortcut to circumvent proper engineering and tuning, sort of how mechanical ventilation hijacked the architecture industry.  And now nearly a century later after the advent of mechanical ventilation, we have droves of buildings that simply cannot function without an HVAC system and a grove of lost knowledge related to building ventilation that was common prior to HVAC.
    So in another generation, vehicles will probably be extremely quiet, but turn the noise cancellation off (or it fails) and your 2035 Cadillac will be as noisy and vibratory as an 1980 VW diesel Rabbit.

    • 0 avatar

      Nissan did active noise canceling in one of it’s JDM Bluebird (called the Stanza over here) in 1992. God only knows how I remembered this bit of trivia….

  • avatar
    Robert Schwartz

    Where have they been. Noise cancellation has been available in headphones for years now. Far better to use it that to load cars up with asphalt sound deadener.

  • avatar

    So we have here a brilliant technology that TTAC uses to bash GM and call out the SUVs for their fuel economy.
    Yep…just another day.

    • 0 avatar
      Greg Locock

      Silvy, how do you know it is a brilliant technology? How did you assess its brilliance? Is it more brilliant or less brilliant than solving the problem the normal way?

      FWIW active noise cancellation has been around for 25 years, for cars. I installed and tuned a protype ANC in a GM vehicle in 1989, about the same time as Nissan had it in production.

  • avatar

    So, in order to save some gas, GM is lugging the engine causing a characteristic sound which they can’t tune out so they wind up using noise cancelling tech in the audio system. Not too elegant, but it  doesn’t make GM a bad person. I believe some Hondas have had this for a while.

    • 0 avatar

      Well amazingly, Toyota just rolled this out in Japan in the Crown there to address ‘engine rotational noise’.

      Wonder if they’ll write a piece about that too?

    • 0 avatar

      “If” Honda has this, it ain’t workin’!!   Our last CRV was loud and buzzy.  Our current Pilot isn’t much better, we ofter think a door or window is ajar when they are not.  Just sayin’.

  • avatar

    Is lugging the engine for economy a good idea even without the noise? Seems like over the expected life of the motor that would eventually cause problems. longevity of vehicles is more important to buyers than ever before.

    • 0 avatar

      Nope.  The execs who run the auto companies expect leasing to continually increase in popularity.  Eventually, vehicles will only last about a year longer than the lease.

  • avatar

    Honda has used this same technology for years on the Odyssey, a vehicle that was road-noisier than all of its competitors.  The better question is why is GMC still around???  Gas is going up again and will keep going up.  The future is not 2 truck brands.  I say ditch GMC, combine Cadillac and Buick dealers, and put the focus on selling more Chevy Silverados, Tahoes, Suburbans, etc.  Give the Theta Terrain to Buick and sell it at a higher price. GM is now selling more vehicles with 4 nameplates than it did with 8.  Maybe they can do better with 3.  Get rid of the GMC distraction and let Silverado challenge F-150 for best in sales.

    • 0 avatar

      GMC was kept alive because individually as a brand it was profitable. I actually agree that GMC should not have been kept, but the beancounters won.

      Buick and Cadillac should not be combined.

    • 0 avatar

      The Cadillac and Buick dealers should be combined NOT the brands themselves.  This would allow a much greater number of vehicles sold per dealer and would give a Cadillac-Buick dealer a broader array of luxury vehicles that are very different to sell.  There shouldn’t be much difference in how a Buick (Lexus) customer is treated versus a Cadillac (BMW) one.  Keeping GMC is tantamount to keeping Buick’s and Chevrolet’s hands tied for the sake of how things are versus how they should or could be.  Selling “Professional Grade” pickups at a luxury dealer makes no sense.  But the old guard at GM (you know, the ones that screwed everything up in the first place) were the ones that convinced the auto bailout committee to support keeping GMC.  No vision.

    • 0 avatar

      Yeah, GMC as a division just seems very redundant, I am not sure what the difference from a Chevy is other than big square fender flares.  I can only assume closing the dealerships would have been too much expense/headache etc.

    • 0 avatar

      If GMC is profitable and people continue to go to their showrooms, why get rid of them?
      You cannot expect everyone who would normally buy a GMC pickup, if discontinued, to automatically purchase a Chevy from now on.  Some might venture to Ford, Dodge, and (ghasp) Toyota or Nissan.
      If I were in the market for a new full size truck, GMC would probably be my only stop.   If GMC were discontinued,  I don’t think I’d get a Chevy… Even though they are 95% identical.    I believe there is a perception (true or not) that GMC is a grade above  your run of the mill Chevrolet truck.

    • 0 avatar
      Some Guy

      The armchair CEOs are out in full force.

    • 0 avatar
      Acc azda atch

      Find me someone AT GM who knows what the hell is going on over there…
      How to sell and market vehicles correctly
      How to get someone to BUY a GM vehicle.. because it is the best there is and not cause of the WARRANTY..
      ANd I will show you 2000 people who sit around on their sofas.. and watch the TV show ONE LIFE TO LIVE starring GM and the REN CEN who got a better idea of how to run a MANUFACTURING company.. than the current barrage of STUPID TELECOM CEO

  • avatar

    Most CUVs are quieter than the Honda CR-V, because Honda doesn’t believe in sound insulation.

  • avatar

    I see, it is just another day at TTAC and another chance to bash GM – even though there is a strong claim that there is no editorial, nope, nope, can’t say the b word and I don’t mean Bettlegeuse.

    Lets see, Acura’s been doing this since 2005 – so is it shame on Acura?

    Toyota does it in Japan on the Crown – shame on Toyota?

    For that matter, Lotus has been doing it since 1990.

    Nope, no b-word here, nope, nope, nope. Much better for GM to put a metric ton of sound deadening into the Theta so TTAC can complain about it being overweight instead.

  • avatar

    Get rid of the 18-20″ alloy’s would do wonders on sound dampening and ride quality.

  • avatar

    It’s a cool idea, and if it works, great.  How does it effect the sound quality of the speaker system when playing music?  Does it cause distortion, or does it cut out when the radio is on?  If you are listening to something that has audio in the same frequency as the engine drone, is it going to suppress that as well?

    • 0 avatar

      I don’t know about the GM system specifically but in general these systems will ignore the desired sound from the radio and not affect it.  The microphones will of course pick up the desired sound from the radio as well as the undesired engine/road noise sound; however the system “knows” what sound is coming out of the radio and can electrically subtract this from the microphone’s signal so the the radio sound is not cancelled out.

  • avatar

    I guess it’s an improvement over GM’s usual method of compensating for engineering shortcomings – cranking up their marketing hype machine to 11.

  • avatar

    Screw suppressing engine and road noise.  Tune that sucker to cancel out the better half.  Talk about a world of improvement!  Not my spouse, of course…the rest of your wives…

  • avatar

    From my experience this system actually works incredibly well.
    GM needs to extend it to the Buicks too because the LAF isn’t exactly a K24Z3.  It should probably go into the Malibu, Cruze LTZ, and vehicles with the boat anchor 3.0L as well.

  • avatar

    We have known this system is in there and it isn’t the only noise cancellation system to go into a car either.  I am not sure what the point of the article is.

    • 0 avatar

      It’s to remind the TTAC readership how GM continually uses subpar technology to mask its own engineering failures, of course.
      Try to follow along, Steve-O: in the name of fuel efficiency, GM is deliberately hiding from owners the noises of protest an engine makes when being forced to lug along. Those noises exist for a reason, a very good one, but GM chose to hide that. Of course that lugging will cause mechanical difficulties down the line for anyone foolish enough to try to keep their GM CUVs longer than 3-4 years… but that doesn’t matter when the only game in town is pushing an IPO, baby!
      GM’s remedial engineers chose this noise-masking “solution” over other, better methods, because they simply can’t do any better. They’re simply unable to design a better engine from the start. FAILING that, those remedial engineers could have culled at least 300 lbs from the overweight Thetas… but, ah, no, GM couldn’t figure out how to do that either while maintaining structural rigidity (maybe those remedial engineers should ask their counterparts at Hyundai — HYUNDAI, for chrissakes — how they did it.)

      FAILING that, maybe GM’s marketeers could have spec’ed the Terrain without heavy 20″ chrome rims… no, wait, that would mean the company could risk alienating GMC’s increasingly gangsta-wannabe customer base, and we can’t have that.
      So here we are, with yet another complicated and inelegant “solution” from GM. Oh, and as Ed mentioned — after all that, GM still FAILED to appreciably raise mileage in the first place.

  • avatar

    I’ve seen noise cancellation in the Ecotec motors for at least the past 6 years. Hardly anything new from GM as they have had this technology in place for some time now. 

  • avatar

    I wonder how it works?  One of the things that I like about my DTS is how wonderfully quiet it is.  Both inside and outside noises are almost not there, its awesome. I wonder if these technologies can quiet down my Golf, which is way more fun, but way more noisy.

  • avatar
    Acc azda atch

    Ya could just put some sound deadening under the hood, thicker / laminated glass…
    Wouldn’t know the difference.
    On the other hand..
    If the motor doesnt sound right… well people in these damn things wouldnt know any better anyway.

  • avatar

    It’s about time.  This technique has great potential to reduce vehicle weight.  Sound deadener, insulation, thick glass, etc. all weigh a lot, and can be thinned out with active cancelation.

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