Headphones

Earbuds or Earphones

Headphones (also known as earphones, earbuds, stereophones, headsets, or 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.

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.

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 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 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.

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).

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.

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. Examples include: AKG K501, Audio-Technica ATH-A900, Beyerdynamic DT880, Sennheiser HD650, Sony MDR-V6, Koss Pro/4AA.

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.

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 [1].

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 portablity 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 sound isolation. Because of the individualized labor involved, custom canalphones are far more expensive.

Driver types

Dynamic

The dynamic driver is the most common type used in headphones. This principle consists of a magnetic element attached to a thin diaphragm, which is often a paper material. The diaphragm is actuated by a voice coil, oscillating it and inducing vibrations into the air producing sound. The magnetic element in headphones are often composed of ferrite, mostly in lower-end or very cheap headphones. In most modern or high-end headphones, the driver is made out of aluminium, neodymium, or titanium. It should be noted, however, that driver material alone doesn't determine the sound quality of any pair of headphones.

Electrostatic

A thin, electrostatically charged diaphram (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 the 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 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 (the 5 Pro utilizes dual armatures) and the Shure E5C, combine an armature driver (for high frequencies) and a small dynamic driver (for low frequencies), but are generally more expensive than other canalphones.

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.

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 closed 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 unconfortable when using them in laying on ones 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. 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 stethescopes. It was sometimes used in inexpensive airline headphones, although Sennheiser had a cordless model on the market for a short period.

Dangers & 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.

It should be noted that 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.

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.

A controversial theory holds that canalphones (which sit directly in the ear canal, much as earplugs do) are actually safer than open-air headphones. 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 sounds very well, and noise cancellers do not attempt to attenuate high-pitched sounds.

Benefits

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.

Prominent manufacturers of headphones

External links

The Audio Circuit - Information on and user reviews of loudspeakers, headphones, amplifiers, and playback equipment
Types of Headphones
Head-Fi: High Fidelity Headphones Discussion Forums
Headphone Gallery & Archive - Database of Headphone Specifications and Images
Headset Benefits
Headwize: A Resource Site for Headphones and Headphone Listening
MVHeadphones: Noise Isolation vs. Noise Cancelation
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.