Earphone (or headphones in the early days of telephony and radio) is a pair of small loudspeaker drivers worn on or around the head over a user's ears. They are electrostatic transducers, which convert an electrical signal to a corresponding sound. Earphones 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. Earphones are also known as ear speakers, earphones and supra-aural headphones use a band over the top of the head to hold the speakers in place.