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New approach to noise cancellation

Raymond de Callafon
Raymond de Callafon

If a tree falls in the forest and nobody hears the crash, it may not be news; however, when the noise inside an airplane cabin or in the air-handling system of a large building is significantly reduced, Raymond de Callafon cheers.

In a report in the April 4 issue of the Journal of Sound and Vibration, de Callafon, a professor of mechanical and aerospace engineering, described a new mathematical algorithm that Ph.D. candidate J. Zeng and he designed to dramatically improve noise-cancellation technologies by destructive interference.

“Noise cancellation is a hidden technology that most consumers aren’t aware of, but vehicles made by BMW, Mercedes, Honda, and other companies are now using it,” says de Callafon.“Our new technique should greatly expand the potential of active noise-cancellation technologies.”

Basic “feedforward” active noise-cancellation is composed of a microphone that measures incoming noise, a computer processor that converts that information into anti-noise instructions, and an audio speaker that broadcasts sound waves that are exactly 180 degrees out of phase with the unwanted signal and of the same magnitude. Unfortunately, feedforward noise cancellation is plagued by noisy acoustic feedback.

“We’ve developed a totally new approach that works by generating the feedforward noise cancellation signals and adaptively changing them in the presence of acoustic coupling,” de Callafon says. “This has been a complicated problem to solve and we think the approach we’ve taken will have a significant impact on the field.”

A technique invented by Raymond de Callafon improves the ability to achieve destructive interference of an electronic chirp (left) and white noise (right) emitted by a commercial air-handling system. (purple signal, unfiltered sound; green signal, after noise cancellation). A technique invented by Raymond de Callafon improves the ability to achieve destructive interference of an electronic chirp (left) and white noise (right) emitted by a commercial air-handling system. (purple signal, unfiltered sound; green signal, after noise cancellation).
A technique invented by Raymond de Callafon improves the ability to achieve destructive interference of an electronic chirp (left) and white noise (right) emitted by a commercial air-handling system. (purple signal, unfiltered sound; green signal, after noise cancellation).