Headphones

From Wikipedia, the free encyclopedia

Contents 1 History 2 Applications 3 Types of Headphones 3.1 by Form Factor 3.2 by Driver Technology 3.3 by Earcup Enclosure 3.4 by Positioning 4 Benefits and Limitations 5 Dangers and volume solutions 6 See also 7 References 8 External links

Headphones (also known as earphones, earbuds, stereophones, headsets, or by the slang term cans) are a pair of transducers that receive an electrical signal from a media player or receiver and use speakers placed in close proximity to the ears (hence the name earphone) to convert the signal into audible sound waves. In the context of telecommunication, the term headset is also commonly understood to refer to a combination of headphones and microphone used for two-way communication, for example with a mobile phone.

[edit] History

Headphones date back to the early days of the telephony and the radio.^[1] The telephone earpiece such as the one pictured at the left was common around the turn of the 20^th century. Sensitive headphones were about the only way to detect some of the weakest electrical signals of the early instruments. 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 with both stationary equipment (e.g. CD or DVD player, home theater etc.) and portable devices (e.g. digital audio player/mp3 player, mobile phone, etc.). Headphones are also often used with the personal computer. Some headphone units are portable and self-contained, incorporating a radio receiver and battery power. Other headphones are cordless and use some form of wireless technology (e.g., radio such as analogue FM, Bluetooth, Wi-Fi, or infrared signals) to receive the audio information via signals from a base unit.

Another application is in the professional audio sector. Headphones are used in live situations by disk jockeys (DJ) and sound engineers for monitoring channels independently from what the public hears. In radio studios, DJs use a pair of headphones when talking to the microphone while the speakers are turned off, for reduced feedback and monitoring of their own voice. In studio recordings, musicians and singers use headphones to play along to a backing track.

Headphones are normally attached to an audio device through a connector, the so-called jack plug. The two common connectors are 1/4" and 3.5 mm plugs. Headphones designed for home stereo systems and recording studios use the older 1/4" connector. Sony introduced the 3.5 mm connector in 1979, adapting the older monophonic 3.5 mm connector for use with its Walkman personal stereo. Advantages of the smaller connector include lower bulk, weight and cost. This smaller connector is more prevalent today due to the popularity of portable music devices, although aftermarket headphones sometimes include an adapter for compatibility with the larger connector. In the professional world, only 1/4" is used, although professional headphones often come with an adapter to 3.5 mm.

[edit] Types of Headphones

[edit] by Form Factor

• Circumaural. Circumaural headphones^[2] have pads that go around the ears, usually very large and very comfortable. This is the type commonly used in recording studios and among audio enthusiasts.

• Supra-aural. Supra-aural headphones^[3] have pads that go on top of the ears. They were commonly bundled with personal stereos during the 1980s.

• Earbuds/Earphones. 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 precision and range of sound offered by many full-sized headphones and canalphones. 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.^[4]

During the 1990s, earbuds became a common type bundled with personal music devices; for example, the headphones included with the iPod are earbuds.

• Canalphones. Canalphones, also known as interruptible foldback systems (IFB), are earbuds that sit directly inside the ear canal. Although canalphones offer portability similar to earbuds, it often acts as an earplug to block out environmental noise (utilizing “closed-canal” technology to create an acoustic seal).

There are two main types of IFBs — 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 IFBs are more expensive than universal IFBs.

[edit] by Driver Technology

The drivers are the primary provider of sound in the headphones.

• Dynamic. The dynamic driver is the most common type used in headphones. This 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.

• Electrostatic. A thin, electrostatically charged diaphragm (typically a coated PET film membrane), is 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 membrane 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.

Typically electrostatic headphones are more expensive than dynamic, and are relatively rare.^[5] 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.

• Balanced armature. Usually used only in canalphones (due to their diminutive size and low impedance), such as Etymotic, Shure, Sensaphonics, Ultimate Ears and Westone. They generally are limited at the extremes of the hearing spectrum (<50Hz, >16kHz) and require a seal more than other types of drivers to deliver their full potential. Some canalphones, like the Ultimate Ears super.fi 5EB, combine an armature driver (for high frequencies) and a small dynamic driver (for low frequencies), for the benefit of lower costs. For the higher-end models, such as super.fi 5 Pro and the Shure SE420/E5, two balanced armature drivers were utilized for a more balanced picture. Flagship models such as the Ultimate Ears UE-10, Shure E500/SE530, and Westone ES3 employ three balanced armature drivers with a view to enhance the sound towards perfection. However, multiple-driver earphones tend to have the problems of inaccurate spacing and emphasis in the bass department, thus losing some fidelity. This is compensated by a couple of technologies, such as routing a balanced armature to handle a dedicated range of notes, utilizing a specialized port (or air duct) to allow air to flow through the armature for increased efficiency, and utilizing inline crossovers to ensure accurate reproduction of high, mid, and low notes to rectify these weakness.

Besides the construction of the actual sound producer, the amount of “load” or impedance on the line is an important differentiating factor among headphone design. Many common headphones using a dynamic driver resting on or slightly in the ear have 32 ohms impedance. Smaller, in-the-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 other. Often portable devices designed to work with low-impedance headphones are unable to drive high-impedance headphones to high levels of sound.

[edit] by Earcup Enclosure

• Open. Open headphones (sometimes marketed as “open air” headphones) have an open grille on the back of the driver, exposing the driver to the outside, and allowing the 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 easily heard by others in the vicinity of the user (not always a desirable quality). They, however, usually have less sound distortion (due to the lack of resonance) and tighter controlled sound reproduction. Most audiophile-quality headphones, such as the AKG K-501, Grado GS1000, and Sennheiser HD 650 are open headphones.

• Closed. Closed headphones have a sealed backing, which attenuates sound waves propagating in the direction 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 (typically a 10 dB decrease in outside sounds). A sealed chamber is often claimed to have a negative effect of distorting sound in certain instances and providing “boomier”, less controlled bass. Examples of closed headphones: AKG K271S, Audio Technica ATH-A900, Sennheiser HD-280 Pro, Sony MDR-V6, Koss Pro/4AA, Ultrasone HFI-550, Beyerdynamic DT-770, Rystl SH-400.

[edit] by Positioning

• Over the head. The traditional style of headphones has a band or bands over the top of the head. This is especially prevalent for heavier headphones such as circum-aural designs, which would otherwise slip downward due to their weight.

• Behind the head. Designs with the headband behind the head are usually used in portable supra-aural headphones. They do not disturb one's hair like an over-the-head headband does, and can be worn with hats, etc. However, they are very uncomfortable when using them in lying on one's back or when sitting on a chair with headrest. This now-common style, sometimes referred to as "street-style," was popularized by Sony.

• Clip. The earpiece is secured with a clip that wraps around the base of the pinnae (outer ear), similar to eyeglass temples (thus potentially uncomfortable for anybody wearing eyeglasses). Usually used with earbuds, but also sometimes used with supra-aural headphones or canalphones.

• In-ear. Earbuds and canalphones sit on the concha of the pinnae or directly in the ear canal.

• Around the ear. The earbuds are wrapped around the ear then put into the ear. Most used when the earbuds keep falling out of the ear because the earbud is too big or the ear is too small.

• Under the chin. This style is very rare in consumer headphones, using a U-shaped tension band suspended beneath the chin to hold transducers in the ears, similar to the design of stethoscopes. It was sometimes used in inexpensive airline headphones, although Sennheiser had a cordless model on the market for a short period.

• Around the neck. Some people prefer to hang their headphones around their neck, with the volume turned all the way up so that they can still hear the music. This allows the wearer to listen to other things, e.g. someone talking, while still listening to their music.

[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.) Headphones of the 'closed back' type are also used to exclude external sounds, particularly in sound recording studios and in noisy environments. 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, 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 our 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, though, because, historically, loudspeaker listening was 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. This typically happens in the left earpiece at the connection junction. ^{[dubious — see talk page]}

[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 is 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 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, one may manipulate the volume tags, or Replay Gain, of MP3s; this method must be manually done by the user using 3rd-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 decry this as an infringement on personal choice, and use 3rd-party options to reverse the software volume caps placed on such devices. Others 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.

Canalphones (which sit directly in the ear canal, much as earplugs do) 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/headphones is blocked out by canalphones, therefore allowing the user to listen at lower volumes without having to turn up the listening device (possibly to unsafe levels) to compete with background noise. (Canalphones are a passive counterpart to active noise cancellers, which use circuitry and destructive wave interference to attenuate sound). Manufacturers of canalphones quote that their products reach an isolation level 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-pitched sounds.

[edit] See also

• Noise-cancelling headphone
• Loudspeaker
• Subwoofer (Stereo separation)
• Microphone
• Headphone amplifier

[edit] References

1. ^ It has been speculated that headphones were invented by Nathaniel Baldwin of Utah in 1910.[1]
2. ^ Examples include: AKG K501, Audio-Technica ATH-A900, Beyerdynamic DT880, Sennheiser HD650, Sony MDR-7506, Koss Pro/4AA, Ultrasone HFI-2200 ULE, Bose QuietComfort 2 and Around-Ear (first released as TriPort) headphones. NB: these products are listed only as being common models of the circumaural design. No endorsement of the respective brands/models is implied.
3. ^ Examples include: Grado SR-60, Koss Porta Pro, Sennheiser PX-100, Ultrasone iCans, Bose QuietComfort 3) headphones. NB: these products are listed only as being common models of the supra-aural design. No endorsement of the respective brands/models is implied.
4. ^ http://www.ear-hearing.com/pt/re/earhearing/abstract.00003446-200412000-00001.htm
5. ^ Examples of electrostatic headphones are Koss ESP/950, Stax SR-007 Omega II, and Sennheiser HE90 “Orpheus”. NB: no endorsement of the respective brands/models is implied.

[edit] External links

• The Audio Circuit - Information on and user reviews of loudspeakers, headphones, amplifiers, and playback equipment
• Types of Headphones, Koss website
• Headphone Gallery & Archive - Database of Headphone Specifications and Images
• Headwize: A Resource Site for Headphones and Headphone Listening
• HeadphoneReviews.org-A sister site of the Head-Fi forums; reviewers rate their headphones on criteria like bass extension/quality, comfort, soundstage, etc. No reviews of common, low-cost headphones.
• Head-Case: Ad and Commercial Free, just-the-facts Forum Site for Headphone Fans.
• Headphonesguru : a resource site for headphones - tests, projects, DIY, articles, products, links.
• Head-Fi: Covering Headphones, Earphones and Portable Audio
• Headphones and Audio IRC Chat room (Java applet)