What are Circumaural Headphones?
Circumaural headphones (also called full size headphones) are headphones that completely surround the ears. Headphones which are circumaural (literally meaning "around the ears") allow for the user's ears to be fully enclosed and are designed to fully seal against the head, thus providing a great deal of isolation from the outside, which serves to attenuate unwanted external noise in the background.
Because of its large encompassing characteristic and, thus, the isolation that it provides, circumaural earcups are the chief type of earcups that are used for noise-cancelling headphones. Since circumaural headphones enclose the ear completely with their earpads, they allow for very little acoustic intake of sound from the outside, thus providing passive noise cancellation for noise-cancelling headphones. Circumaural headphones achieve this by using large circular or ellipsoid earpads. These earpads, made up of high-density foam, serve as sound-absorbing material to block out sound so they can't penetrate through the earcup foam and reach the user's ears. Using this method, circumaural headphones can block out a substantial amount of background noise in any environment.
The tradeoff of circumaural headphones is their large size. Because their earcups and surrounding earpads are so large (to fit completely over the person's ears), circumaural headphones can be very cumbersome to travel with and make for an inefficient and poor model for ease of portability. But what is lost in portability is gained in reduction of outside noise, allowing a user to listen to his or her headphones with less intrusive, unwanted background noise.