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.
History
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.
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; headphones used in telegraph and telephone work had an impedance of 75 ohms. Those used with early wireless radio had to be more sensitive and were made with more turns of finer wire; impedance of 1,000 to 2,000 ohms was common, which suited both crystal sets and triode receivers.
In early powered radios, the headphone was part of the vacuum tube's plate circuit and had dangerous voltages on it. It was normally connected directly 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.
Applications
Headphones can be used both with fixed equipment such as CD or DVD players, home theater, personal computers and with portable devices (e.g. digital audio player/mp3 player, mobile phone, etc.). Cordless headphones do not need to be connected via a wire, receiving a radio or infrared signal encoded using a radio or infrared transmission link, like FM, Bluetooth or Wi-Fi. These are actually made of powered receiver systems of which the headphone is only a component, these types of cordless headphones are being used more frequently with events such as a silent disco or Silent Gig.
Headphones are widely used for listening to audio sources for recreation. In the professional audio sector headphones are used in live situations by disc jockeys with a DJ mixer and sound engineers for monitoring signal sources. In radio studios, DJs use a pair of headphones when talking to the microphone while the speakers are turned off, to eliminate acoustic feedback and monitor their own voice. In studio recordings, musicians and singers use headphones to play along to a backing track. In the military, audio signals of many varieties are monitored using headphones.
Wired headphones are attached to an audio source. The most common connectors are 1/4" and 3.5 mm stereophonic jack plugs and sockets. The older 1/4" standard is used on professional equipment, and is often used on fixed equipment. Sony introduced the smaller, cheaper, and now widely-used, 3.5 mm "mini" stereo connector in 1979, adapting the older monophonic 3.5 mm connector for use with its Walkman portable stereo tape player. Adapters are available for converting between 1/4" and 3.5 mm devices.
Types of headphones
There are many different types of headphone designs, with the listening situation and the needs of the listener determining what type of headphone will be used. Generally, headphone formfactors can be divided into four separate categories: circumaural , supra-aural , earbud , and in-ear .
Earcup headphones
Earcup or on-ear headphones rest on the exterior of the ear and were the earliest headphone form designed.
The housing, or earcup , of an earcup headphone will be either open or closed. Open headphones, sometimes marketed as “open air” headphones, have an open grille on the back of the earcup, exposing the driver to the outside and allowing sound waves to propagate away from the ear freely. This backing type does not isolate the listener from outside sounds; in addition, sound through open headphones can be heard by others in the vicinity of the user. They usually have less distortion due to the lack of earcup resonance. Closed headphones have a sealed backing, which attenuates sound waves propagating away from the ear. As a result, listeners away from the headphones cannot hear the produced sound easily. In addition, sound from outside is attenuated by the sealed backing, providing a level of isolation to the listener. A sealed chamber is often claimed to have the negative effect of distorting sound in certain frequencies due to resonances within the earcup housing, however, bass frequencies are stronger in a sealed chamber headphone design.
Circumaural
Circumaural headphones (sometimes called full size headphones ) have circular or ellipsoid earpads that completely surround the ears. Because these headphones completely surround the ear, circumaural headphones are often noise-isolating and sealed, but cheaper ones usually are not. Because the earpads must enclose the ear, circumaural headphones are often larger in size and tend to weigh more, making them somewhat less portable, but their size also allows for a larger driver. This type of headphone is commonly used in recording studios and by audio enthusiasts.
Supra-aural
Supra-aural headphones have pads that sit atop of the ears, rather than around them. They were commonly bundled with personal stereos during the 1980s. This type of headphone generally tends to be more lightweight.
Earbuds
Earbuds or earphones are headphones of a smaller size that are placed directly outside of the ear canal, but without fully enveloping it. They are generally inexpensive and are favored for their portability and convenience. However, due to their inability to provide isolation, they are not capable of delivering the same dynamic range offered by many full-sized headphones and canalphones for a given volume level. As a result, they are often used at higher volumes in order to drown out noise from the user's surroundings, which increases the risk of hearing-loss. During the 1990s and 2000s, earbuds became a common type bundled with personal music devices.
In-ear headphones
Canalphones
Main article: In-ear monitorCanalphones (also known as in-ear monitors , or IEMs ) are earphones that are inserted directly into the ear canal. Canalphones offer portability similar to earbuds, and also act as earplugs to block out environmental noise. There are two main types of IEMs: universal and custom. Universal canalphones provide one or more stock sleeve size(s) to fit various ear canals, which are commonly made out of silicone rubber, elastomer, or foam, for noise isolation. Universal canalphones are typically marketed to casual listeners and are relatively inexpensive, though some offer very high audio quality.
Custom canalphones are fitted to individuals. Castings of the ear canals are made, usually by an audiologist. The manufacturer uses the castings to create custom-molded silicone rubber or elastomer plugs that provide added comfort and noise isolation. Because of the individualized labor involved, custom IEMs are more expensive than universal IEMs.
Technology
Headphone transducers employ one or more of several methods of sound reproduction.
Moving-coil
The moving coil driver, more commonly referred to as a "dynamic" driver is the most common type used in headphones. The operating principle consists of a stationary magnetic element affixed to the frame of the headphone which sets up a static magnetic field. The magnetic element in headphones is typically composed of ferrite or neodymium. The diaphragm, typically fabricated from lightweight, high stiffness to mass ratio cellulose, polymer, carbon material, or the like, is attached to a coil of wire (voice coil) which is immersed in the static magnetic field of the stationary magnet. The diaphragm is actuated by the attached voice coil, when an audio current is passed through the coil. The alternating magnetic field produced by the current through the coil reacts against the static magnetic field
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