- Jun 13, 2012
Automakers sound off on unwanted noise
Fire up the new Ford Shelby Mustang GT500 and you're greeted with the sort of raucous exhaust note that would make a Harley-Davison owner quiver with delight. Slip inside a Lexus LS460 and it'll be nearly as quiet as a tomb.
"The loudest sound you ever hear is the first rattle in a new car."
While features like design and performance help define a brand, few things distinguish a product's character like sound. So, it's no surprise that manufacturers are putting more effort than effort into managing vehicle sound characteristics.
But, "It's not just about how loud a car is," suggests Kara Gordon, who oversaw noise-related work on the 2013 Chevrolet Malibu. "The quality of the sound also matters. And even little things can have a big impact on your perception of a vehicle," she says, suggesting, "The loudest sound you ever hear is the first rattle in a new car."
Traditionally, automotive engineers took a pretty straightforward approach to dealing with what was routinely referred to as the "N" in the trio of attributes known as NVH – short for Noise, Vibration and Harshness. And, indeed, all three go together. Reduce vibrations and harshness and noise usually drops way down, making your vehicle a lot more pleasant to drive.
The three biggest sources of unwanted noise come from the wind, the road and the engine compartment.
The simplest way to deal with unwanted sounds is to stiffen up the chassis, add insulating foam and blankets and perhaps turn to trick features like laminated side glass. It also helps to improve a vehicle's aerodynamics, suggests Vishnu Jayamohan, chief North American product planner for the 2013 Nissan Altima, who notes that the three biggest sources of unwanted noise come from the wind, the road and the engine compartment.
Aerodynamics, of course, serve a dual purpose since the slicker a vehicle's shape the better its fuel efficiency. So you're seeing makers invest in more sophisticated technologies like the full underbody pan on the Chevrolet Malibu Eco.
Mirrors are a particularly difficult challenge as one of the most significant sources of wind noise, which is why Chevrolet downsized the new Malibu's mirrors and Ford has mounted them on the sheetmetal, rather than the window pillar of the new Fusion. Those odd blisters on the Nissan Leaf headlamps, meanwhile, direct air away from the battery-car's side mirrors.
Getting noise under control is a particularly difficult challenge with electric vehicles because of what engineers call the "stumps-in-the-swamp syndrome." With all the familiar engine noises gone, you're suddenly aware of the gravel crunching under tires, the whirring of motors and the whistling of fans.
Simply tossing mass at the problem isn't the answer.
Simply tossing mass at the problem isn't the answer because the heavier an electric vehicle gets, the shorter its range. Then again, the same goes for even a mainstream, gasoline-powered vehicle like the Altima, says Nissan's Jayamohan. The fourth-generation sedan is expected to be the lightest model in the midsize segment – and deliver the highest highway mileage rating.
So, to bring noise levels under control, Nissan had to take some creative steps, such as the use of a new lightweight sound barrier in the headliner made from a modified version of 3M's familiar Thinsulate material. It also borrowed a trick from some of its competitors, using a flocked plastic under the wheel wells that doesn't resonate when splashed with rain or pummeled with gravel.
Automotive engineers are no longer limited by NIH, or the Not-Invented-Here syndrome. They're even lifting ideas from the aerospace world. Honda is one of several makers that has adopted the same basic noise cancellation technology that makes it so much more pleasant to fly these days. But instead of relying on tight-fitting headphones, the Accord sedan and Odyssey minivan uses its speaker system to cancel out some of the more unpleasant noises that would typically echo through the cabin.
The 2013 Lincoln MKS offers an interesting twist on the noise cancellation concept. In this case, engineers wanted to not just cancel out unwanted road noises but also enhance the sound of the sedan's engine.
That's not uncommon. Porsche and Ferrari, to name two exotic brands, have come up with various ways of beefing up the sound of their exhaust, in some models literally piping the sound into the passenger compartment. But Lincoln's approach is to amplify the sound on the front speakers, just enough that it appears you're actually hearing the engine itself.
Settle back into your seat and enjoy the sound and the fury. It's likely been carefully tuned for your enjoyment.
You can expect to see manufacturers make even more extensive use of active noise controls in the years ahead, though it won't replace good engineering and more traditional solutions like sound-deadening insulation or laminated glass.
Whatever the approach a manufacturer takes, the results can be significant. It's not uncommon to see the latest models deliver noise level reductions of three, six, even nine decibels. That may not sound like much, but sound is measured logarithmically, so those numbers mean cutting your original noise level to half, a quarter or an eighth. And that means that even in the highest-power muscle cars, like the GT500, you can hold a conversation at highway speeds – unless, of course, you've got your foot pressed to the floor. In that case, settle back into your seat and enjoy the sound and the fury. It's likely been carefully tuned for your enjoyment.