acoustic shadow

noun

: an area where sounds from a nearby source that should normally be audible cannot be heard because of an unusual combination of factors (such as topography and wind)

During the American Civil War, observers noted a curious fact: the sounds of a battle, clearly distinguishable at ten miles, could be utterly inaudible at two. These weird wrinkles in the landscape were called "acoustic shadows."

—Mark Slouka, Harper's, June 2000

Word History

First Known Use

1830, in the meaning defined above

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