Headphones are a pair of small loudspeakers, or less commonly a single speaker, held close to a user’s ears and connected to a signal source such as an audio amplifier, radio, CD player, or portable media player. They are also known asstereophones, headsets or, colloquially, cans. The in-ear versions are known asearphones or earbuds. In the context of telecommunication, the term headset is used to describe a combination of headphone and microphone used for two-way communication, for example with a telephone.
The telephone earpiece, such as the one pictured at the right, was common at the beginning of the 20th century. Headphones originated from the earpiece, and were the only way to listen to electrical audio signals before amplifiers were developed. The first truly successful set was developed by Nathaniel Baldwin, who made them by hand in his kitchen and sold them to the U.S. Navy.
Very sensitive headphones such as those manufactured by Brandes around 1919 were commonly used for early radio work. These early headphones used moving iron drivers, either single ended or balanced armature. The requirement for high sensitivity meant no damping was used, thus the sound quality was crude. They also had very poor comfort compared to modern types, usually having no padding and too often having excessive clamping force to the head. Their impedance varied; headphones used in telegraph and telephone work had an impedance of 75 ohms.