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Unless you have a pair of noise-canceling headphones, flying can be annoying to the ears. A lot of low-pitched rumbling makes it into the cabin. Problem is, the wings, floors, ceilings and bulkheads are lined with a lightweight material with a honeycomb structure—which adds structural integrity to the aircraft—but engine and airflow sound cuts right through.
"The physical law says that the lighter the material is, the worse it can block sound." Yun Jing is an acoustician at North Carolina State University.
In a quest for quiet, he and his colleagues constructed a similar material—but with a quarter-millimeter thin layer of latex stretched across the cells of the honeycomb. In tests, the latex-laced structure cut the intensity of low-frequency rumbling to a thousandth of its previous level—enough, he says, to make an airplane cabin sound more like a peaceful living room. The study is in the journal Applied Physics Letters. [Ni Sui et al, A lightweight yet sound-proof honeycomb acoustic metamaterial]
Problem is, the material Jing developed is six percent heavier than the standard stuff. And more weight means more fuel means more expense. But if we settled for a slightly quieter flight, Jing says he could use less latex, making the noise-blocking honeycomb just a few percent heavier. Considering that the honeycomb is already one of the lightest parts of an airplane, you’re then looking at only a modest plane weight gain.
Of course, that's assuming everyone wants a quieter plane. "Some people say they actually want to hear the sound of the engine. They don't want the cabin to be too quiet. They want to make sure the plane is still flying." Sounds like you’ll need those expensive headphones a little while longer.
—Christopher Intagliata
[The above text is a transcript of this podcast.]
