The first headphones were developed in the late 19th century for use by telephone operators, to keep their hands free. Headphones connect to a signal source such as an audio amplifier, radio, CD player, portable media player, mobile phone, video game console, or electronic musical instrument, either directly using a cord, or using wireless technology such as Bluetooth, DECT or FM radio. In the context of telecommunication, a headset is a combination of headphone and microphone. A third type are bone conduction headphones, which typically wrap around the back of the head and rest in front of the ear canal, leaving the ear canal open. Another type, known as earbuds or earpieces consist of individual units that plug into the user's ear canal.
Circumaural ('around the ear') and supra-aural ('over the ear') headphones use a band over the top of the head to hold the speakers in place. Headphones are also known as earspeakers, earphones or, colloquially, cans. Headphones let a single user listen to an audio source privately, in contrast to a loudspeaker, which emits sound into the open air for anyone nearby to hear. They are electroacoustic transducers, which convert an electrical signal to a corresponding sound. Headphones are a pair of small loudspeaker drivers worn on or around the head over a user's ears.
