The Rolls-Royce Silver Cloud II was introduced in 1959 with the slogan “At 60 miles an hour, the loudest sound comes from the electric clock.”
These days, that might not be quiet enough. Modern cars have become so silent that people notice things they never did, says Paul Williamsen, product education manager at the University of Toyota in Torrance, Calif.
“The little remaining noises are the ones you never used to hear, like the sound of the wind around the wiper blade or the sideview mirror or the electric fuel pump,” he says. “I can hear the fuel pump in my neighbor’s V-8 from my front yard.”
And in a world where technology moves fast, the latest car is the quietest.
A surprising example is the 2005 Land Rover LR3, which looks like a couple of shoeboxes on wheels. According to Edmunds.com, which tests all cars on the same stretch of highway, the LR3 generated only 63 decibels internally at 70 m.p.h. and idled at less than 50 decibels. Considering that normal conversation produces 60 decibels, it’s no wonder that 50 was too quiet for the meter to record.
In comparison, Edmunds.com tested the Volkswagen W12 Phaeton, the company’s $96,000 flagship, in 2004, and recorded 70 interior decibels at 70 m.p.h. In 2003, the $256,000 Bentley Arnage registered 73 decibels at that.
The LR3 was designed using aerodynamic bucks, or wooden models, computerized pressure measurements and acoustic holography, says chief program engineer Steve Haywood.
He said these tests led Rover to install “a tuned harmonic absorber fitted to an interior roof bow” to eliminate “road-induced boom,” the drumming that results when vibration from the tires matches the harmonic of the car body.
Quiet operation was the domain of the luxury cars–you could balance a penny on edge on the grille of an idling 1906 Rolls-Royce Silver Ghost–until the late 1980s, when premium brands Acura and Lexus started sharing technology with their mainstream cousins, Honda and Toyota.
“It’s hard to distinguish between `real’ luxury cars and `near’ luxury cars these days,” says Williamsen. “They’re all a lot quieter than a decade ago.”
“Luxury vehicle owners expect to seal out the noise in their vehicles, but economy buyers tend not to focus on noise as much,” said Dan Kahn, road test editor at Edmunds.com. “For sports car owners, noise is a factor but in a different way–most of those drivers want to hear the motor and know they have a powerful car.”
The latest weapons in the noise battle are steel-laminates, counteractive sound systems and tires that tread quietly.
Several automakers, including GM, Ford, Chrysler and Mercedes, are using “quiet steel,” in which two layers of steel are separated by a polymer. Ford was the first with the 1999 Explorer.
Greg Corda, marketing manager for the steel’s producer, Material Sciences Corp. in Farmington Hills, Mich., says the metal sandwich effectively turns noise into minimal heat, which disperses.
“Manufacturers used to allow noise into the cabin, then try and deaden it. Now they design the body to prevent noise from entering,” Corda said. “The technology started in the 1980s with the brake industry, trying to solve brake squeal. Then it spread to powertrains and engines [valve covers in diesel motors for example] and finally into bodywork.”
The next significant application will be the cowl plenum, the area around the windshield, which includes the dash, roof and A pillars, he says. “It’s attached and it vibrates and rain hits it–it’s all noise coming right at you.”
As far back as 1990, Lexus used foam-filled A-columns on the LS400 to control noise, according to Williamsen.
Tiremakers also are working to conquer the three types of noise, according to Hideo “Hank” Hara, executive vice president of Bridgestone’s North American Tire technical center in Akron.
“The first is airborne noise. You can hear the sound of the tire rolling, like a voice. The second is vibration. The road hits the tire, creates vibration to the wheel, the wheel to the suspension and the suspension to the vehicle. Each vehicle makes a different sound; we match the construction of the tire to different cars.”
The third is the wheel cavity, Hara said. “The tire is an air chamber, like a timpani or a kettle drum and 250 hertz equals the key of C. If you put a small chamber inside the larger one, it doesn’t make any noise. That’s simple physics.”
Exhaust technology has even found a way to muffle a muffler.
Corsa Performance in Cleveland has a muffler developed from an idea by retired NASA scientist Ron Huff. It’s grown into a $20 million company annually.
Huff’s idea is a free-flowing muffler in which the soundwaves are 180 degrees out of phase and cancel each other out, says Jim Browning, who started the company in 1989.
The Corsa muffler was introduced on the 1997 Chevrolet Corvette.
“We take out specifically high frequencies. 110 decibels at 100 hertz is very uncomfortable, but get it down to 85 decibels at 100 hertz and people don’t think about it.” (A lawnmower registers 85 decibels and a motorcycle 95).
And though the system is silent at light throttle, it’s throaty under hard acceleration.
“People love that,” says Browning. “They’re bold when they want to be.”
But perhaps the most interesting research into noise reduction comes from Honda, which has developed a system of noise cancellation emitted through the stereo speakers of the Acura RL and the Honda Odyssey minivan.
“There was a low frequency boom in the RL–when you’ve got 300 horsepower you’re going to have a throaty exhaust note,” said John Watts, manager of product planning at Acura. “The engine management system on the Odyssey goes from 6 cylinders to 3 in time of low power need, so we tuned the system to keep that noise out of the cabin.”
The effect can be an eerie quiet, says Kahn of Edmunds.com, who recalls a strange experience in Los Angeles:
“Inside, the car was perfectly silent. Then, at the light I could hear a song, but I had the radio off. I looked over at the guy beside me, and it was his stereo. The system was cutting out all the background noise of the city, but it was letting in his stereo noise through the speakers in my car.”
