headphones

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.

History

Headphones date from the beginnings of the history of the telephone and the radio. The weak electrical signals of the early instruments were enough to operate only headphones audibly. Beyerdynamic is considered to have officially invented headphones in the late 1930s, and was the first company to market headphones to the public.^[1][2]

Applications

Headphones are normally detachable, using a jack plug. Typical products to which they are attached include the walkman, mobile phone, CD player, Minidisc player, digital audio player (MP3 player), and personal computer. Headphones can also be used with full-size stereo components. Some headphone units are self-contained, incorporating a radio receiver. Other headphones are cordless, using radio (for example analogue FM, digital Bluetooth, Wi-Fi or infrared) signals to receive signals from a base unit.

Another application is in the professional audio sector. Here, headphones are used in live-situations by DJ's and sound engineers for monitoring channels independently from what the public hears. An effect can also be previewed this way. In radio-studios diskjockeys use a pair of headphones when talking in 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 a backing track. These headphones tend to be of better quality than 'normal' headphones.

The two common connectors are 1/4" and 3.5 mm plug. Headphones designed for home stereo systems and recording studios use the older 1/4" connector. Sony introduced the 3.5mm connector in 1979, adapting the older monophonic 3.5mm 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. Please note that in the professional world, only 1/4" is used. Therefore, professional phones are actually 1/4" oriented and always include an adapter to 3.5 mm.

In theory, all microphones are speakers and vice-versa. People can use a microphone as a speaker or the left channel of a pair of headphones for a microphone. However, microphones and headphones are different in frequency response. Headphones, especially more expensive ones, will have a large bass response but thin mids and highs. Microphones will sound very undetailed in the high end, and will sound light on the bass end. Therefore, while it is not fully necessary, it is recommended that microphone are to be used as microphones and headphones are to be used as headphones.

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 modes 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 (though claims such as 'frequency response 4 Hz to 20 kHz' and are just marketing hype based on the fact that the headphone has some output at 4 Hz, however 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 offscreen sound (such as the footsteps of an opponent).

Although modern headphones are very widely sold and used for listening to stereo, especially since the invention of the Walkman, they are fundamentally unsuited to such use. This is why they usually 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 at each ear they create the phase difference which our brain uses to locate direction (at least below 2 kHz). 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 spacial 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 spacial effect from stereo on headphones by using frequency-dependent cross-feed between the channels, or better still a Blumlein shuffler (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 when the actual recording is done, with artificial pinnae can convincingly take away the middle-of-the-head effect. Optimal sound can only be 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. You can also have a room full of people using computers to mix audio tracks all at the same time.

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, and 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. Also of note, the French government has imposed a limit on all music players sold in the country: they may not be capable of producing more than 100 dbA (the threshold of hearing damage during extended listening is 80 dB, and the threshold of pain, or of immediate hearing loss, is 130 dB). 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. Also, most European countries have imposed high penalties since 2002 on drivers not using a headset while operating a mobile phone in a car, to ensure that drivers keep their hands on the vehicle's controls.

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 (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 -30-40 dB, while noise cancellers isolate by a degree of -15-20 dB. 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.

Types of headphones

In descending order of size:

Circumaural

Circumaural headphones have pads that go around the ears, usually very large and very comfortable. This is the type typically used in recording studios and among audiophiles. Examples include: AKG K501, Audio-Technica ATH-A900, Beyerdynamic DT880, Sennheiser HD650, Sony MDR-V6, Koss Pro/4AA, Ultrasone HFI-2200 ULE.

Supra-aural

Supra-aural headphones have pads that go on top of the ears. They were commonly bundled with personal stereos during the 1980s. Examples include: Grado SR-60, Koss Porta Pro, Sennheiser PX-100, Ultrasone iCans, Bose QuietComfort 3.

Earbuds/Earphones

Earbuds (American English) or Earphones (British English) are small headphones 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.^[3]

During the 1990s, they became the most common type bundled with personal music devices. For example, the distinctive white headphones included with the iPod are earbuds.

Canalphones

Canalphones, also known as in-ear monitors, are earbuds that sit directly inside the ear canal. They offer portability similar to earbuds but with greater sound isolation, and often deep bass response.

There are two main types of canalphones — universal and custom. Universal canalphones provide one or more stock sizes of cushions to fit various ear canals (which are commonly made out of silicone rubber, elastomer, or foam). 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 greater comfort and "closed-canal, closed-air" noise isolation (a passive noise cancellation principle that does not require use of batteries). Because of the individualized labor involved, custom canalphones are far more expensive.

Driver types

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 soundwave is generated.

Typically electrostatic headphones are 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.

Examples of electrostatic headphones are the Koss ESP/950, Stax SR-007 Omega II, and the Sennheiser HE90 "Orpheus".

Balanced armature

Usually used only in canalphones (due to their diminutive size and low impedance), such as Etymotic, Shure, Sensaphonics, and Ultimate Ears. They generally are limited at the extremes of the hearing spectrum (>16 kilohertz, <50 hertz) 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 E5C, dual balanced armature drivers were utilized for a more balanced picture. Highest-end models such as the Ultimate Ears UE-10pro and Westone ES3 employs triple balanced armature drivers with a view to enhance the sound towards perfection. However, multiple-drivers earphones tend to have the problem of inaccurate spacing and emphasize in the bass department, thus losing fidelity to a certain extent. This is compensated by added details and a broader soundstage.

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 of load. Smaller, in-the-ear types may have a load as low as 16 or 11. "Studio" and noise-reducing headphones tend to have much higher loads, ranging from 300 in some cases to as high as 5000 ohms in other. The Headphone Ohm List gives some sample ohms for a wide range of consumer headphones.

Usually, higher ohms are correlated with higher quality headphones, but higher ohms means more "load" and therefore a higher power requirement from the sound source.^{citation needed]} This may mean that better or larger headphones will either not sound as loud or run down the battery of a portable device, or that more power may be needed via an external amplifier. For portable devices, over 64 ohms may result in reduced performance.

Backing type

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 soundwaves 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 a more expansive soundstage (due to the lack of resonance) and more tightly controlled sound reproduction; most audiophile-quality headphones, like the ones listed below, are open headphones.

Examples of open headphones: AKG K-501, Grado RS-1, Sennheiser HD-650.

Closed

Closed headphones have a sealed backing, which attenuates soundwaves propagating in the direction away from the ear. As a result, listeners away from the headphones cannot hear the produced sound easily. In addition, extra-soundwaves are attenuated due to the sealed backing, providing a level of isolation to the listener (typically a 10dB decrease in outside sounds). Their sealed chamber generally has the added negative effect of reducing soundstage and providing "boomier", less controlled bass, making them skew lower in price and high-end quality than open headphones.

Examples of closed headphones: AKG K271S, Audio Technica ATH-A900, Sennheiser HD-280 Pro, Sony MDR-V6, Koss Pro/4AA, Ultrasone HFI-550.

Methods of wearing headphones

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 can be 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.

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.

See also

• Noise-cancelling headphone
• Wireless headphones
• Loudspeaker
• Subwoofer (Stereo separation)
• Microphone
• Headphone amplifier
• Head-fi

References

1. ^ http://www.beyerdynamic.com/cms/History.687.98.html?L=0
2. ^ http://www.beyerdynamic.co.uk/brochures/HIFI_E_2002.pdf#search='beyerdynamic%20history'
3. ^ http://www.ear-hearing.com/pt/re/earhearing/abstract.00003446-200412000-00001.htm

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
• Headset Benefits
• A Guide to Headsets
• 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, like low-end Sony earbuds, etc.
• 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.