Earphones, earbuds, are sound transducers that are inserted directly into the ear. Earphones or earbuds are shaped to hook onto the outer ear. Thehousing of the earbud contains a miniature loudspeaker whose sound travels directly to the eardrum via an auditory canal lined with foam rubber.
In addition to this design, there are also in-ear headphones, whose auditory canal is connected airtight to the ear canal. Hence the term auditory canal headphones. The airtight hearing canal produces a much better sound, with even low tones being transmitted directly to the eardrum.
Smallest electrostatic loudspeakers, piezo loudspeakers. MEMS loud speakers or plunger coil loud speakers are built into the earpieces. The frequency range is exceptionally high, covering the complete audio frequency range up to over 20 kHz. The lower frequency depends on whether it is an earphone or an in-ear earphone. While earphones transmit low frequencies of about 200 Hz, in-ear earphones do so at about 60 Hz. This means that in-ear earphones can also reproduce hi-fi. Depending on the speaker principle, the speaker impedance is low impedance, but there are also high-impedance versions. In addition, earphones are characterized by high sensitivity, which may well be 110 dB and higher.
There are wireless and wired versions. In the case of wireless earphones, the signals can be transmitted via radio, infrared light or by means of induction loops. Wireless earbuds use Bluetooth and the corresponding Bluetooth profile. In this case, the Headset Profile( HSP). Wired earphones have miniaturized 3.5 mm jack plugs, which in make versions are also gold-plated. Among the better-known wireless earphones are Apple's AirPods, which work with iPhones, iPods, iPads, smartwatches, with MP3 players and media players.