Headphones

From Wikipedia, the free encyclopedia

Headphones (also known as earphones, earbuds, stereophones, headsets, or by the slang term cans or face plugs) 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 stereophonic, monophonic or binaural audio-frequency signal source such as an audio amplifier, radio or CD player. 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.

Contents 1 History 2 Applications 3 Types of Headphones 3.1 Technology 3.1.1 Dynamic 3.1.2 Electrostatic 3.1.3 Balanced armature 3.1.4 Other types 4 Benefits and limitations 5 Dangers and volume solutions 6 See also 7 References 8 External links

[edit] History

[1] The telephone earpiece such as the one pictured at the right was common around the turn of the 20^th century. Sensitive headphones were the only way to listen to audio signals before amplifiers were developed. Very sensitive headphones such as those manufactured by Brandes (Fig.1) around 1919 were commonly used for early radio work.

[edit] 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.). Some 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.

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 (DJ) 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.

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 and cheaper, and now widely-used, 3.5 mm 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.

[edit] 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. Circumaural headphones have circular or ellipsoid earpads that fit around the ears. This type of headphone is commonly used in recording studios and among audio enthusiasts. Supra-aural headphones have pads that sit on top of the ears, rather than around them. They were commonly bundled with personal stereos during the 1980s. 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.^[1] During the 1990s and 2000s, earbuds became a common type bundled with personal music devices. Canalphones, also known as in-ear monitors, or IEMs, are earbuds 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. 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.

Typically, the housing, or earcup of a 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 resonances. 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.

[edit] Technology

Headphone transducers employ one or more of several methods of sound reproduction.

[edit] Dynamic

The dynamic, or electrodynamic 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 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 flowing through the coil reacts against the static magnetic field in turn, causing the coil and attached diaphragm to move the air, thus producing sound. Modern dynamic headphone drivers were derived from dynamic microphone capsules.

[edit] Electrostatic

Some types of headphones use electrostatic drivers rather than dynamic. Electrostatic drivers consist of a thin, electrically charged diaphragm, typically a coated PET film membrane, suspended between two perforated metal plates (electrodes). The electrical sound signal is applied to the electrodes creating an electrical field; depending on the polarity of this field, the diaphragm is drawn towards one of the plates. Air is forced through the perforations; combined with a continuously changing electrical signal oscillating the membrane, a sound wave is generated. Electrostatic headphones are usually more expensive than dynamic, and are relatively rare. In addition, a special amplifier is required to amplify the signal to oscillate the membrane, which often requires electrical potentials in the range of 100 to 1000 volts. Electrostatic headphones have several advantages over dynamic headphones, including a much faster impulse response and greater detail retrieval due to the extremely thin and light diaphragm membrane, which is often only a few micrometeres thick.

[edit] Balanced armature

A balanced armature is a sound transducer design primarily intended to increase the electrical efficiency of the element by eliminating the stress on the diaphragm characteristic of many other magnetic transducer systems. As shown schematically in the first diagram, it consists of a moving magnetic armature that is pivoted so it can move in the field of the permanent magnet. When precisely centered in the magnetic field there is no net force on the armature, hence the term 'balanced.' As illustrated in the second diagram, when electric current flows through the coil, it magnetizes the armature one way or the other, causing it to rotate slightly one way or the other about the pivot thus moving the diaphragm to make sound.

The design is not mechanically stable, a slight imbalance makes the armature stick to one pole of the magnet. A fairly stiff restoring force is required to hold the armature in the ‘balance’ position. Although this reduces its efficiency, this design can still produce more sound from less power than any other. Popularized in the 1920s as Baldwin Mica Diaphragm radio headphones, balanced armature transducers were refined during World War II for use in 'sound-powered' telephones for military use. Some of these achieved astonishing electro-acoustic conversion efficiencies in the 20% to 40% for narrow bandwidth voice signals.

Today they are typically used only in canalphones and hearing aids due to their diminutive size and low impedance. They generally are limited at the extremes of the hearing spectrum (<20Hz, >16kHz) and require a seal more than other types of drivers to deliver their full potential. Higher end models may employ multiple armature drivers, dividing the frequency ranges between them using a passive crossover network. Some combine an armature driver with a small dynamic driver for increased bass output.

[edit] Other types

Much rarer driver designs include orthodynamic, Air Motion Transformer, and piezoelectric drivers. Orthodynamic, or magnetostatic drivers, are either comprised of a thinly pressed disc made of tightly coiled fine aluminium wire affixed to a mylar sheet or of a printed circuit. This disc is the diaphragm. The diaphragm is then sandwiched between two magnets which have the same polarity facing each other. As a result the magnets repel from each other and so the whole assembly is clamped together. An electrical signal is passed through the disc as it would be through the voice coil of a dynamic driver and the motion produced generates the sound. Once a popular choice for manufacturers such as Yamaha for their headphones, the technology has fallen generally into disuse as companies increasingly favour moving coil designs. Fostex continue to make orthodynamic headphones, although their fidelity is not generally well regarded in comparison with older orthodynamic designs. AMTs and Piezoelectric drivers are very rare in headphones. There is only one AMT and one piezoelectric headphone in current production.

Besides the construction of the sound producer, the amount of “load” or impedance on the line is an important differentiating factor among headphone designs. Many common headphones using a dynamic driver have an impedance of 32 ohms. Smaller, in-ear types may have an impedance as low as 16 or 11 ohms. "Studio" and noise-reducing headphones tend to have much higher impedances, ranging from 300 in some cases to as high as 5000 ohms in others. Portable devices designed to work with low-impedance headphones are often unable to drive high-impedance headphones to high volume levels.

[edit] Benefits and limitations

Headphones may be used to prevent other people from hearing the sound either for privacy or to prevent disturbance, as in listening in a public library. They can also provide a level of sound quality that could only be matched by speakers costing a great deal more. This is especially true in the bass (low frequency) region, where loudspeaker-listening room interactions normally cause resonant nodes, so that even with the best speakers, a listener in a given place hears some bass notes too loudly and others too softly. Good headphones, with a good seal to the ear, can have an extremely flat low-frequency response down to 20 Hz within 3dB. Marketed claims such as 'frequency response 4 Hz to 20 kHz' are usually overstatements; the product's response at frequencies lower than 20 Hz is typically very small. Those of the 'closed back' type are also used to exclude external sounds, particularly in sound recording studios and in noisy environments. Headphones have been reputed to better portray subtle layers of sound.^[2] Headphones can also be useful for videogames that use 3D positional audio, allowing players to better judge the position of an off-screen sound source (such as the footsteps of an opponent).

Although modern headphones are widely sold and used for listening to stereo recordings, especially since the invention of the Walkman, some say they are fundamentally unsuited to such use. They supposedly produce the disconcerting effect of sound coming from the middle of the listener's head, with unnaturally isolated sounds occasionally appearing predominantly in one ear, giving the impression that the other has suddenly gone deaf. This is because stereo recordings represent the position of each sound by large amplitude differences between two channels intended for reproduction through a pair of loudspeakers. When the sounds from the two speakers mix, they create the phase difference the brain uses to locate direction. Others claim that stereo sounds better through headphones, because the right and left channels haven't mixed. This makes panning effects more easily appreciated, and adds a sense of immersion to the listening experience. Binaural recordings use a different microphone technique to encode direction directly as phase, with very little amplitude difference (except above 2 kHz) often using a dummy head, and can produce a surprisingly life-like spatial impression through headphones. Commercial recordings almost always use stereo recording, because historically loudspeaker listening has been more popular than headphone listening. It is possible to improve the spatial effect from stereo on headphones by using frequency-dependent cross-feed between the channels, or—better still—a Blumlein shuffler (a custom EQ employed to augment the low-frequency content of the difference information in a stereo signal), though this is rarely done. While cross-feed can reduce the feeling of deafness in one ear, only the use of a dummy head during recording, with artificial pinnae, can convincingly take away the "middle of the head" effect. Optimal sound is achieved when the dummy head matches the listener's head, since pinnae vary greatly in size and shape.

Headphones can have an ergonomic benefit over the traditional handset at office desks. They save space and many new models are wireless. They also allow call center agents to maintain good posture instead of tilting their head sideways to cradle a handset. They are also used in professional sound editing, so that more than one person can work on an audio track without interfering with another.

Over time, many wired headphone cables fail. A common scenario in which a replacement set might need to be purchased is the physical breakdown of copper wiring within the cords of many popular headphones. Over time, the connection formed to close the circuit may become severed due to stress fatigue.

[edit] Dangers and volume solutions

Using headphones at a sufficiently high volume level can cause temporary or permanent hearing impairment or deafness due to an effect called "masking." The headphone volume has to compete with the background noise, especially in excessively loud places such as subway stations, airplanes, and large crowds. This leads to the disappearance of the normal pain associated with higher levels of volumes. Extended periods of the excessively loud volume are extremely damaging. Some manufacturers of portable music devices have attempted to introduce safety circuitry that limited output volume or warned the user when dangerous volume was being used, but the concept has been rejected by most of the buying public, which favors the personal choice of high volume. Koss introduced the "Safelite" line of cassette players in 1983 with such a warning light. The line was discontinued two years later for lack of interest.

In recent years, interest has once again focused on protecting hearing, and companies have responded. Sony's AVLS feature corrects differences in track volumes as they are being played, and Apple's Sound Check normalizes the peak volumes of selected tracks in iTunes. Also, listeners may manipulate the volume tags, or Replay Gain, of MP3s; this method must be manually done by the user using third-party software, but is regarded to provide better consistency than the above options.

The French government has imposed a limit on all music players sold in the country: they must not be capable of producing more than 100dBA (the threshold of hearing damage during extended listening is 80dB, and the threshold of pain, or of immediate hearing loss, is 130dB). Many users decry this as an infringement on personal choice, and use third-party options to reverse the software volume caps placed on such devices. Still, other users welcome the government's pro-health stance.

Other risks arise from the reduced awareness of external sounds—some jurisdictions regulate the use of headphones while driving vehicles, usually limiting the use of earphones to a single ear. The complete isolation from outside noise can be a hazard in itself, as a user could miss the sound of a car horn and walk into traffic with fatal consequences. Losing situational awareness can also lead to getting robbed, particularly in busy environments where bumping into another person would be ignored, e.g., subway stations.

Canalphones are generally believed to be safer than open-air headphones for use in noisy environments. The reason for this is that much of the external noise which is usually heard while using earphones or headphones is blocked out by canalphones, therefore allowing the user to listen at lower volume levels without having to turn up the listening device to compete with background noise. Canalphones are a passive counterpart to active noise canceling headphones, which use circuitry and destructive wave interference to attenuate sound. Manufacturers of canalphones quote that their products reach isolation levels of -30dB to -40dB, while noise cancellers isolate by a degree of -15dB to -20dB. Closed and noise-cancelling headphones can have a similar effect, although sound attenuation of the latter is usually limited in frequency range and amplitude: closed headphones do not isolate low frequency sounds very well, and noise cancellers do not attempt to attenuate high frequency sounds.

[edit] See also

• Noise-cancelling headphone
• Subwoofer (Stereo separation)
• Headphone amplifier
• TRS connector
• Digital audio player

[edit] References

[edit] External links

• The Audio Circuit - Information on and user reviews of loudspeakers, headphones, amplifiers, and playback equipment
• Types of Headphones, Koss website
• HeadphoneReviews.org-A site where reviewers can rate their headphones on criteria like bass extension/quality, comfort, soundstage, etc. No reviews of common, low-cost headphones.
• Headphone Gallery & Archive - Database of Headphone Specifications and Images
• Headphone burn-in wave files (white noise, pink noise, frequency sweep)
• Headphonesguru : a resource site for headphones - tests, projects, DIY, articles, products, links.
• Sennheiser Headphone Reviews

Headphone Forums and Chat

• Head-Case Ad-free forum for headphone-related discussion.
• Head-Fi Headphones and more forum
• iPod and Headphone Studio Headphone and portable audio forums
• Headwize: A Resource Site for Headphones and Headphone Listening The original home of the high-end headphone community
• Head-Place Very low traffic headphone forums
• Auriculares.org Headphones forum in spanish.
• Headphones and Audio IRC Chat room (Java applet)cs:Sluchátka

da:Hovedtelefoner de:Kopfhörer es:Auriculares eo:Kapaŭskultilo fr:Casque audio ko:이어폰 it:Auricolari he:אוזניות nl:Hoofdtelefoon ja:ヘッドフォン no:Hodetelefoner nn:Hovudtelefon pl:Słuchawki pt:Auscultadores ru:Наушники fi:Kuuloke sv:Hörlurar uk:Навушники zh:耳機