Noise-cancelling headphones reduce unwanted ambient sounds (i.e., acoustic noise) by means of active noise control (ANC). Essentially, this involves using a microphone, placed near the ear, and electronic circuitry which generates an "antinoise" sound wave with the opposite polarity of the sound wave arriving at the microphone. This results in destructive interference, which cancels out the noise within the enclosed volume of the headphone.

Noise cancellation makes it possible to enjoy music without raising the volume excessively. It can also help a passenger sleep in a noisy vehicle such as an airliner. Retail noise cancelling headphones typically use ANC to cancel the lower-frequency portions of the noise; they depend on more traditional methods (like the materials from which the earcups are made) to prevent higher-frequency noise from reaching the ear.

This approach is preferred because: By the 1950s, systems were created to cancel the noise in helicopter and airplane cockpits including those patented by Lawrence J. Fogel in the 1950s and 1960s such as U.S. Patent 2,866,848 (filed in 1954), U.S. Patent 2,920,138, U.S. Patent 2,966,549 and Canadian patent 631,136. Dr.

Amar Bose (founder of the Bose Corporation) began work on his noise-cancelling headphones in 1978 on board an airplane. During the international flight, he was provided with a set of headphones from the airline and almost immediately realized how dissatisfied he was with their quality and the loud engine noise. After nearly a decade of research, Bose would release the first noise-cancelling headphones.

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