headphones

Headphones are a pair of small loudspeakers, or less commonly a single speaker, with a way of holding them close to a user's ears and a means of connecting them to a signal source such as an audio amplifier, radio or CD player. They are also known as earphones, earbuds, stereophones, headsets or, informally cans. 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 around the turn of the 20^th century. From the earpiece developed the headphones. Sensitive headphones were the only way to listen to audio signals before amplifiers were developed.^[1]

Brandes radio headphones, circa 1920

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. Impedance varied, but 1,000 to 2,000 ohms was common, which suited both triodes and crystal sets.

When used with early powered radios, the headphone was normally connected to the positive high voltage battery terminal, and the other battery terminal was securely earthed. The use of bare electrical connections meant that users could be shocked if they touched the bare headphone connections while adjusting an uncomfortable headset.