Noice cancelling headphones — after my piece on noise-cancelling ear plugs, a few people wrote in to recommend noise-cancelling (canceling) headphones. (Sorry — Canadian spelling in use!) Noise-cancelling headphones use a microphone and electronics to create a soundwave at polar oppose to the soundwave coming in. Thise cancels out the noise.
To my surprise, Wikipedia has a fairly lengthy article on noise-canceling headphones.
Have you ever used headphones to block out noise?