More Space for Sound



Sounding Off: A developmental composite
material from Owens Corning and NXT's automotive exciter technology helps
turn door trim panels into loudspeakers.

Novi, MI-Many drivers may like to listen to tunes in the car, but interior suppliers are the ones who have to face the music. Speakers take up space in the door, creating packaging problems. And they drive up assembly costs as well. Now Owens Corning Automotive (www.owenscorning.com) is working on a way to address both problems.

The company has come up with a developmental composite speaker panel that integrates NXT plc's Distributed Mode Loudspeaker (DML) technology (www.nxtsound.com). DML creates sound with the help of a specially designed transducer, or "exciter" that induces resonant vibrations in flat panels. Already well established in consumer audio applications, the technology attracted interest as a way to make automotive sound systems that save space without sacrificing sound quality.

It has, however, not been easy finding panel materials that have the right balance of physical and mechanical properties. "Materials selection has been one of the biggest challenges," says Martin Cassey, NXT's North American applications manager. He cites surface density, stiffness, and inherent damping characteristics as a few key physical properties that determine acoustic performance. Add to those stringent automotive requirements for mechanical properties, thermal resistance, and cosmetics. NXT has been able to use commonplace thermoplastics-such ABS and polypropylene-for a speaker material. But Cassey acknowledges there can be "trade-offs" between sound and structure.

And here's where Owens Corning comes in. The material for its speaker panel has been formulated with both acoustic and structural performance in mind, according to Howard Hiers, the company's global engineering services director. He declined to divulge any details about the material's composition or properties, other than to describe the material as "a reinforced thermoplastic."

Owens Corning's speaker could be implemented in several ways, including partial speaker panels that drop into larger door trim panels, instrument panels, or even pillars. The biggest bang for the buck, however, will probably be designs that create full door trim panels from the speaker material. Hiers notes that this implementation would eliminate the most assembly steps and save the most space. "It would require only about one-third the depth of a conventional cone-speaker assembly," he says.

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