Machine Design

Cool sounds for hot cars

Motion platforms that give users control over six degrees of freedom can be expensive and complex.

For the last 100 years, automakers have basically used two different muffler designs: reactive mufflers with sound-deadening chambers and straightthrough designs in which a perforated pipe is wrapped with acoustic material. But reactive mufflers also trap the "good" engine noises, according to some car enthusiasts. Straight-through designs let too much noise through. And both get louder with age. A third alternative, electric noise cancellation, is too costly and still impractical.

Engineers at Corsa Performance, Berea, Ohio(, have devised a mechanical, sound-canceling muffler. It lets some engine noise escape into tuned chambers. The chambers are sized so that the noise echoes off the back of the chamber so as to arrive back at the starting point 180° out of phase. There it combines with the engine noise and cancels some of it out. According to users, the muffler emits a high-performance sound when accelerating and gets rid of in-cabin resonance at cruising speeds.

The mufflers have to be tuned to specific engines, and currently there are versions for some Corvettes and Vipers. But the company plans to offer mufflers for Camaros and Firebirds, GM cars and trucks, Mustangs, Dodge trucks, SUVs, and several European imports.

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