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Do You Hear What I Hear?

September 10th, 2009

Eberspächer, a German-based company focused on automotive exhaust systems, heaters, and electronics, has recently demonstrated a new product:  a speaker integrated into a vehicle’s muffler, with the capability of significantly affecting the exhaust sound.  “So what?” you might ask.  Well, as described in Automotive Engineering International, there are numerous applications for this technology.

First of all, it could be used to enhance the sound of the tiny little 4-banger – or the quiet rattle of the diesel engine – in our cars.  Conversely, where noise limits are enforced, it could be used to subdue the scream from the high-strung V8 in your Ferrari F430 with the flick of a switch.  (This is done by generating antiphase sound waves – basically, the inverse of the sound being produced from the engine.  The waves cancel each other out – a phenomenon I played around with when I did digital signal processing research in college.  But I’m getting off-topic, and you’re getting bored…)  Furthermore, with talk of the dangers of electric vehicles quietly roaming our city streets, plowing down unsuspecting pedestrians who fail to hear them approaching, the Eberspächer system could be used to produce an exhaust note of any sort to upcoming EVs.

Le Mans PosterHhhmmm.  I’m a bigger fan of a properly tuned exhaust note than most anyone I know.  (To get a sense of what I’m talking about, watch the movie Le Mans in Dolby Digital.  Tell the kids to hush when the Porsche 917 screams down the Mulsanne Straight.  That, to me, is the greatest sound ever made.)  But the automotive purist in me appreciates the fact that these sounds come from the mechanical process that’s moving the car!  Auto OEMs, as well as the aftermarket, have devoted a lot of resources into improving and enhancing the sound coming from our vehicles’ engines.  (Respective examples are the Motor Sound Package offered on various Porsche models in the past, and the fart-can exhausts that people tend to affix to their souped-up Hondas – though any “improvement” from the latter is agruable.)  But they’ve always relied on the engine itself – not some artificial audio source.

Applications making EVs audible might be a more worthy cause, though I tend to think the safety issue there is overblown.  (In cities, where pedestrians are used to crossing the street, people tend to use their eyes as well as their ears to give them an indication of when it’s best to step off the curb.  And at higher, high-way speeds, noise from the tires and air flowing around the car tend to equal that of the engine anyway.)  To me, the most ideal use of this technology might be in PHEVs/EREVs once they’re traveling in charge-sustaining mode (i.e., when the engine comes on to keep the battery charged).  It seems to me that, say, once the engine turns on in the Chevy Volt or Fisker Karma, it would most optimally run at a constant rpm to generate electricity – maintaining this speed whether the car is traveling at a steady speed, accelerating, or even (in some cases) sitting at a stop-light.  That would be a bit unnerving to the driver, who’s used to the engine sound having some sort of relationship with what the car’s doing.  (As an aside – Constantly Variable Transmissions have specific gear-ratios programmed into their software in part for this exact reason.)  Perhaps the Eberspächer system could be used to help recreate the aural experience to which the consumer is accustomed – one more tool to help smooth the transition to electrified vehicles.

Now, go watch Le Mans!

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