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Binaural head in TRW Automotive NVH lab.

"The team's redesign meant re-configuring the stiffeners. It turned out to be a two-step solution process. The added material is cast right into the drum, so it's still a one-piece construction," explains George Schumacher, Senior Manager of CAE/NVH Department for TRW Automotive in Livonia, MI.

Redesigns may be less commonplace once predictive analysis becomes refined. Today's faster computing time, which permits 250,000 to 500,000 degrees of freedom, is a major enabler to advanced predictive NVH analysis. "For model year 2003-2004 production platforms, the team will use predictive models to solve NVH issues. That will enable us to conduct noise screening on the computer using entire system models (axles, knuckles, suspension) before prototype parts are built," says Schumacher.

Although dampening and deadening sounds remain a common method to hinder noise paths, Siemens Automotive is developing a unique approach to enhancing desirable sounds. "We recognize the subjective nature of NVH," says David Geran, Director, Business Development for Siemens Automotive Powertrain Air Induction Division in Windsor, Ontario, Canada.

Satisfying consumer wants does follow patterns. For instance, the public expects a sports car's engine to sound different from a luxury car's engine. "A V6 engine could have an enhanced growl in one application, but purr like a kitten in another application because we can focus on frequency sounds via the air induction system to create a noise signature," Geran says. As an engine accelerates through higher and higher rpms, electronics could be used to null and void certain frequencies that only occur at certain rpms.

"We're working on electronic cancellation of noise frequencies, which is different from passive resonators that only address one noise frequency. By using electronics to cancel or enhance sounds, plastic hollow resonators could be eliminated. That's a huge issue from a packaging and cost standpoint," explains Geran.

Ford Motor Company engineers plotted a comprehensive vehicle, systems and components engineering approach on a new vehicle platform. "We set very specific goals/targets relating to NVH," Tom Lahvic, Ford Motor Company's Vehicle NVH Department Manager for Research and Vehicle Technology, says about 2000 Lincoln LS and Jaguar S-Type. "There was no unique technology used to address NVH, it's just conventional techniques executed very well."

Even small components influenced sound quality on the luxury cars powered by a new 3.9-L V8 DOHC engine. "It's probably the stiffest bracket design we've ever had. Each of the engine-to-body brackets are a small, pyramid shaped design. The design of the engine was driven by achieving noise and vibration goals." Noise and vibration targets helped Ford engineers bypass costly and time consuming re-engineering.

"NVH can be an Achilles' heel because it can actually slow or delay the release of a product," Lahvic says. Since a vehicle's interior is the ending route for NVH, a cabin devoid of unwanted noises helps generate and maintain vehicle brand loyalty.

"If seats are properly designed, they can absorb more than half the sounds reaching the inside of a vehicle," says Mike Dinsmore, Manager of Business Development and Product Planning for Acoustics and Materials at Johnson Controls, Inc. in Holland, MI. More than 60 seat cover materials are undergoing standardized acoustics measurement tests at Johnson Controls as part of the supplier's concentrated efforts to design and engineer improved NVH seat systems.

Although other interior zones such as instrument panels, headliners, and carpeting possess untapped noise absorption possibilities, seats are a primary focal point. "Right now, seats have the most potential for improved interior noise control. There's not much yet being done with instrument panels as a noise absorber, and one reason is because of knee bolsters, airbags, and other structural concerns," Dinsmore says.

In the future, tools that help engineers develop noise-appropriate vehicles may mix subjective and objective considerations. "The trend is to develop scientific models to predict subjective responses. That's an important goal because we are designing our cars to satisfy the subjective impressions of real customers," expresses Muller-BBM's Feng. In the meantime, automakers and suppliers use other methods to predict consumer NVH preferences.

"We do not know how to model how humans perceive the noises of a vehicle, which is why we rely very heavily on jury testing," as well as objective measurements, concludes Peter Laux, PhD, and technical expert in acoustic integration at Johnson Controls.