This Door Strikes the Right Note

Even the best sounding car audio system can give engineers a real headache when it comes time to find room for the speakers. For the 2005 Ford Mustang, Visteon came up with a patented door trim design that makes it easier and less costly to package the subwoofers.

This one-piece door trim, which took home the grand prize during the Society of Plastics Engineers' Blue Ribbon Awards, is a showpiece of function integration. It incorporates an 8-inch subwoofer enclosed within a 12-liter hermetically sealed acoustic chamber. And it also integrates an important side impact feature.

Visteon injection molds the door trim from glass-filled polypropylene. The chamber portion starts out as a separate molding. But the company uses a vibration welding process to attach it to the rest of the trim, creating the hermetic seal in the process. In the past, by contrast, these sealed acoustic chambers for the subwoofers tended to be blow molded and packaged somewhere other than the door-in the rear package tray, for example.

As for the material, Visteon engineers opted for a 10-percent-glass-filled, 12-percent-impact- modified polypropylene from Ferro Corporation. Bob Stafford, Visteon's door trim engineering manger, says the material was specially formulated for this application, which needed sufficient stiffness to support the weight of the speaker and ductility for side impact performance.

One key advantage of the new design comes down to delivering a big sound while minimizing both power requirements and, more importantly, packaging space. Ford and Visteon optimized the acoustic chamber for sound quality. "The enclosed woofers provide a lower distortion," says Stafford. And he points out that the 2005 Mustang uses just two woofers but still plays 8 db louder than previous Mustang models, which had four woofers. In terms of power, he continues, the old four-woofer systems required 2.6 times the current amplifier power to get to the same output as the new integrated system.

The parts consolidation from the new door trim only starts with the elimination of the two woofers. Stafford notes these big speakers required their own trim components. For example, a 6 mm-thick package tray subassembly held the two extra woofers and their amplifiers in many previous Mustang models. Getting rid of the subassembly not only saves money but also "frees up trunk space," Stafford notes.

And aside from having two fewer woofers to package, the system also eliminated the need for a separate pelvic cushioning component in the door. Instead, Visteon engineers designed the acoustic chamber with a collapsible wall in the side impact zone. "The wall allows us to meet side impact performance requirements without the use of a standard hip bolster," Stafford says.

And of course, all this parts integration saves weight and money. Stafford estimates that the new door trim system saves about 18 lb and more than $40 per vehicle.

Future applications for the new door system include trucks, which tend not to have as much room to package the woofers. "We're excited about this door system in the future truck market," says Stafford. "You'd end up with some great sounding trucks."