2016-11-10 21:58:21
Wheels: Giving Today’s Car a Well-Tuned Interior

IT can make engines sound like purring pussycats — or growling tigers.

Through the wizardry of digital technology some of today’s most sophisticated vehicles, like the GMC Sierra Denali, are designed to keep annoying engine noise from seeping into the cabin.

Others, like the Lexus NX F Sport, include digital tuners to accentuate the engine’s throaty growl to satisfy the primal urges of driver and passengers.

And sometimes — in a seeming contradiction — the same car does a bit of both.

In the Nissan Maxima, for example, noise-cancellation technology helps suppress undesirable droning frequencies from the engine. But the throb of horsepower is acoustically amplified when the driver steps on the gas.

“It’s about the driver’s comfort,” explained Aaron Gauger, a product planning manager at Nissan. “But we also want the driver to have a good experience during acceleration.”

All of this, like so much else in modern automobiles, happens through the magic of digital software and hardware.

“There are many companies that are using noise cancellation to make your ride quieter,” said Grant Courville, a senior director at the software company QNX, a BlackBerry subsidiary whose technology is used in Chrysler, Ford and Honda vehicles. Suppressing noise digitally can reduce the need for insulation, helping to make vehicles lighter and thus improving fuel economy.

Noise cancellation can also improve the accuracy of voice recognition for navigation systems and other controls in cars. In addition, it can make it easier to appreciate the music from sophisticated onboard audio systems, or even make it easier to have conversations in the capacious cabin of a seven-seater S.U.V.

Noise cancellation systems use multiple microphones (usually positioned near the driver’s and passengers’ ears in the liner of the vehicle’s ceilings) to detect sounds in the interior, isolating particular unwanted wavelengths and frequencies. Software and digital signal processors then use the car’s audio system to create countervailing waveforms that are broadcast over the speakers to block the original noise.

Not all unwanted sounds can be eliminated. The noises in and around a car — like the whine of tires on different surfaces, the rush of wind through an open window or a road crew’s jackhammers — are too varied and changing to cancel out completely.

“We can’t create a cone of silence — yet,” said Alan Norton, senior technical leader for audio quality at Ford.

Bose, which has been working on active noise cancellation with automakers including Nissan and General Motors since 2010, says the technology is necessarily more complex than that employed in the company’s familiar noise-canceling headphones, which some travelers wear on jetliners to block the steady droning of engines.

“Headphones cancel broadband noise,” explained John Pelliccio, a product manager in the automotive division at Bose. “The noise canceling that we do in cars is designed to go after specific engine harmonics.”

That can mean eliminating lower-frequency engine sounds, some of which result from newer fuel-saving designs. Cylinder deactivation, for example, which can turn off four cylinders in a V8 at cruising speed to save gas, may also generate booms, throbs and other noises that may make drivers think something is wrong with the car.

Mr. Pelliccio said Bose’s active noise canceling can reduce such annoyances by tapping into the car’s computers to determine the status of the cylinders and the engine load in real time, and making the necessary acoustical adjustments.

The technology relies on complex algorithms that are tuned to specific vehicle interiors, accounting for reflective glass surfaces, the position of passengers, and even such details as whether there are cloth or leather seats.

“There’s also a signature to every engine,’’ Mr. Pelliccio said, “and automakers are particular about which harmonics they want to enter the cabin and which ones they don’t.”

That is where the ability to enhance engine sounds can come into play. Because the current generation of smaller, more fuel-efficient engines and turbochargers often does not generate the sort of throaty resonance drivers expect, automakers design systems to augment the sonic experience.

In some ways it is a tradition that stretches back at least as far as the 1960s with Thrush’s hot-rod mufflers. But unlike those chrome-plated exhaust pipes, which were meant to spur the admiration — or annoyance — of people on the street, today’s digital engine enhancements are usually aimed at the driver and passengers inside the car.

“What we do is essentially the same,” Mr. Pelliccio said, “except we’re doing it electronically and playing it through the speakers.”

He noted that consumers in different parts of the world have different opinions on what constitutes a “good” engine sound. In the past, for example, car companies might have had to design different exhaust systems for a European car and an American model of the same car.

“Today,’’ Mr. Pelliccio said, “we can just change the software.”