Silence is golden

Listen up. I SAID LISTEN UP!

The auto industry thought the increasingly fickle U.S. car and truck buyer wanted quiet. Conventional wisdom luxury nameplates such as Lexus and Infiniti proved no noise was good noise.

Wrong, Wrong, WRONG.

For openers, the pursuit of classic NVH (noise/harshness/vibration) attributes can create major league problems. Consumer Reports magazine says a BMW 325i failed a normally routine government crash test because NVH zealots strengthened the car's structure to the point where it no longer had the crush rates originally engineered into it to handle the 30-mph (48 km/h) barrier crash.

Consumer Reports also riled the troops at Chrysler Corp. recently by dropping the LH midsize cars and Grand Cherokee Jeeps from its recommended list, citing owner feedback about NVH issues such as annoying squeaks, rattles and buzzes. Chrysler says it has identified and corrected 300 problems on the LHs that were causing squeaks and rattles.

Beyond that, these days the wizards in the wondrously high-tech Big Three NVH labs have discovered that yet again the truth is as complex as the equations they pour over in search of answers. There is good noise. There is bad noise.

And most complicated of all, your idea of good noise may be my idea of bad.

"It's not just quiet," says Dr. Robert V. Lust, a staff research engineer in General Motors Corp.'s Engineering Mechanics Dept. "It's quiet, and do you like what you hear?"

"We've gotten into a field called sound quality," observes Ford Motor Co.'s Rudy Kunze, chief engineer-core and advanced vehicle attribute engineering. "It's not the level of noise or the absence of noise, but the frequency composition of noise."

Notes 25-year Chrysler Corp. veteran Ken Buczek, supervisor of the company's new $23 million NVH laboratory and test complex: "In the old days, almost any noise in the car was a bad noise. You'd just be flogging and you'd end up with a product that never really hit what the customer was talking about. Now we go for overall sound quality rather than for noise levels."

Complicating the formula is the simple fact that the definition of pleasant sound quality isn't a one-size-fits-all proposition. Obviously Dodge Viper owners are listening for something Cadillac buyers don't want to hear. But experts also note that the increasing number of female truck buyers has significantly altered what was once considered ideal truck NVH levels.

The elusive search for the differences in pleasant sound quality that distinguish a Pontiac Firebird customer from a Lincoln Continental driver has taken the industry in a number of directions.

Chief among them are increasingly complex acoustic computer models that attempt to predict from early engineering drawings and specifications what subtle sounds a future model may make. Those simulations take so many calculations that it can take even the most advanced Cray computers, processing billions of bits per second, 10 to 18 hours to do the run. Out of the miles of data that the supercomputers generate come some fairly offbeat ways to interpret the information.

At Chrysler, for example, one of the staff experts is a music fan who assigns musical notes to the frequency spectrums being studied then plays them on an electronic keyboard. "He finds discordant chords, and says you don't want to have this frequency line up with that frequency because then people will think it's a bad sound," shrugs Chrysler's Mr. Buczek. "We've started playing around with the same thing when we do engine noise."

Changing sound rather than totally eliminating it is the name of the game these days, says Ford's Mr. Kunze. "Noise cancellation, vibration cancellation, we'll see a lot more of that in the future. There's quite a lot of research on materials, active elements to either compensate for noise in the passenger compartment or reduce vibration into the body structure," he says.

NVH characteristics even come under criticism if they're too good. Some buff types complain that super-quiet cars like Lexus take the fun out of motoring.

And as they pursue super-quiet cockpits, more than one engineer has been baffled by the emergence of sounds or rattles they hadn't heard before, such as ticking clocks or the faint whir of odometer cables.

Whether it's the quality race or unbridled competition to please customers, NVH is getting increasingly serious attention. Body structures on most new vehicles are being upgraded for greater stiffness, a chief factor in reducing NVH. Such new models as Chrysler's 1996 NS minivans and GM's new Oldsmobile Aurora, Buick Riviera and new-generation J-body subcompacts all boast enhanced structures. Buick engineers also designed a new firewall sound-deafening system to reduce engine and other outside noise.

Already in the available parts bin are active engine mounts (see WAW - March 1993 p. 101) that produce anti-phase vibrations. They are expensive, says Ford's Mr. Kunze, but they might become fairly widely available in luxury cars before the turn of the century.

In the day-to-day world of automaking, robust engineering (see WAW - March 1994 p.51) and involvement of NVH experts early in the new product-development process are aimed at ending the long list of fixes for NVH problems developed on the assembly line. Once known as "Band-Aid engineers," NVH experts at one automaker solved an idle-shake problem in a popular car line by turning the bumper into a dynamic vibration absorber.

"NVH has always been known as a weight-adder, a cost-adder," says Chrysler's Mr. Buczek. "Our thing has been to try and get out of that mode."

The basics of advanced NVH technology are shared by most of the world's automakers these days. Common are such details as a Belgian acoustic measuring system or dynamometer rolls replicating specific pieces of pavement. Those are all made by a single English firm. Any serious player has elaboate, computerized benchmark tests of any serious competitor, allowing comparison of everything from exhaust notes to tire compounds.

"We all use the same technology," says GM's Dr. Lust.

But how each uses that technology in increasingly competitive NVH rankings may be crucial. If there are any long-range magic bullets lurking in the relatively new focus on sound quality as key to NVH leadership, they're in computer models.

Dr. Donald J. Nefske, senior staff research engineer in GM's Engineering Mechanics Dept., has been working on NVH simulations since 1975. He only grins when asked if he feels like a fast-ball pitcher discovered late in his career. "There's been a lot of interest lately," he notes.

But he cautions that computers and his modeling software aren't ends unto themselves. "It's not so much an issue of whether you could go from a computer model to hardware today and have an acceptable vehicle. You want it to be more than just acceptable. You want it to be world-class. You can't design purely from the model."

Experts at Ford and Chrysler agree - at least in general terms.

Among the computer-committed, virtual reality these days is one of the hot buttons (see WAW - Nov.'94 p.33). Theoretically, a computer-driven virtual reality system would allow everyone from designers to marketers to sit inside a highly realistic, three-dimensional mockup of a new model and quickly change any part of the car or truck using a variety of electronic magic wands.

Everybody's working on the idea, but in an automotive world driven by financial and marketplace realities, those closest to it are cautious. Ford, for example, has a project under way. "It's in the pilot stage at the moment," says Mr. Kunze. "But it costs a lot of money, computer power and modeling technology."

Maybe, he says, early in the next century it will be "a professional tool."

There will remain, however, a need for the traditional touch, says Chrysler's Mr. Buczek. "You still need the hardware. You still want to put your hands on something. I think most engineers are still the kind of people who say, `Give me the thing and let me feel it,"' he says.

These days it may be more important to hear what it sounds like.