Headphones either have wires for connection to a signal source such as an audio amplifier, radio, CD player, portable media player or mobile phone, or have a wireless receiver, which is used to pick up signal without using a cable.
They are sometimes known as earspeakers or, colloquially, cans. The in-ear versions are also known as earphones or earbuds. In the context of telecommunication, a headset is a combination of headphone and microphone.
The particular needs of the listener determine the choice of headphone. The need for portability indicates smaller, lighter headphones, but can mean a compromise in fidelity.
Headphones used as part of a home hi-fi do not have the same design constraints and can be larger and heavier. Generally, headphone form factors can be divided into four separate categories: circumaural, supra-aural, earbud, and in-ear.
Circumaural
Circumaural headphones (sometimes called full size headphones) have circular or ellipsoid earpads that encompass the ears. Because these headphones completely surround the ear, circumaural headphones can be designed to fully seal against the head to attenuate external noise. Because of their size, circumaural headphones can be heavy and there are some sets that weigh over 500 grams (1?lb). Ergonomic headband and earpad design is required to reduce discomfort resulting from weight.Supra-aural
Supra-aural headphones have pads that press against the ears, rather than around them. They were commonly bundled with personal stereos during the 1980s.This type of headphone generally tends to be smaller and lighter than circumaural headphones, resulting in less attenuation of outside noise.
Supra-aural headphones can also lead to discomfort due to the pressure on the ear as compared to circumaural headphones that sit around the ear. Comfort may vary due to the earcup material.
Open or closed back
Both circumaural and supra-aural headphones can be further differentiated by the type of earcups:Open-back headphones have the back of the earcups open.
This leaks more sound out of the headphone and also lets more ambient sounds into the headphone, but gives a more natural or speaker-like sound and more spacious "soundscape" - the perception of distance from the source.
Closed-back (or sealed) styles have the back of the earcups closed. Depending on the model they may block 8-32db of ambient noise, but have a smaller soundscape, giving the wearer a perception that the sound is coming from within their head. One reason for this is that there are sounds reflected back towards the ear.
Ear-fitting headphones
Earbuds
In-ear monitors extend into the ear canal, providing isolation from outside noise. ?
Earbuds and earphones refer to very small headphones that are fitted directly in the outer ear, facing but not inserted in the ear canal; they have no band or other arrangement to fit over the head.(However, many consumer-quality in-ear-canal systems are also called earbuds by their manufacturers.) The outer-ear earphones are portable and convenient, but many people consider them to be uncomfortable and prone to falling out.
Various models are available, starting at very low prices. They provide hardly any acoustic isolation and leave room for ambient noise to seep in; users may turn up the volume dangerously high to compensate, at the risk of causing hearing loss.
On the other hand, they let the user be better aware of their surroundings. Since the early days of the transistor radio, earbuds have commonly been bundled with personal music devices. They are sold at times with foam pads for comfort.
In-ear headphones
In-ear headphones, like earbuds, are small and without headband, but are inserted in the ear canal itself. They are sometimes known as canalphones. Price and quality range from relatively inexpensive to very high; the better ones are called in-ear monitors (IEMs) and are used by audio engineers and musicians as well as audiophiles.Canalphones offer portability similar to earbuds, block out much environmental noise by obstructing the ear canals, and are far less prone to falling out. When used for casual portable use they block out sounds which can be important for safety (e.g., approaching vehicles).
- Universal canalphones provide one or more stock silicone rubber, elastomer, or foam sleeves to fit various ear canals, for correct placement and best noise isolation.
- Custom canalphones are fitted to the ears of the individual user: castings of the ear canals are made, and the manufacturer uses the castings to create custom-molded silicone rubber or elastomer plugs that provide added comfort and noise isolation.[13] Because of the individualized labor involved, custom IEMs are more expensive than universal IEMs; resale value is very low as they are unlikely to fit other people.
Headset
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A headset is a headphone combined with a microphone. Headsets provide the equivalent functionality of a telephone handset with hands-free operation.Among applications for headsets, besides telephone use, are aviation, theatre or television studio intercom systems, and console or PC gaming. Headsets are made with either a single-earpiece (mono) or a double-earpiece (mono to both ears or stereo).
The microphone arm of headsets is either an external microphone type where the microphone is held in front of the user's mouth, or a voicetube type where the microphone is housed in the earpiece and speech reaches it by means of a hollow tube.
Some headsets come in a choice of either behind-the-neck or no-headband design instead of the traditional over-the-head band.
Telephone headsets
Telephone headsets connect to a fixed-line telephone system. A telephone headset functions by replacing the handset of a telephone. Headsets for standard corded telephones are fitted with a standard 4P4C commonly called an RJ-9 connector. Headsets are also available with 2.5mm jack sockets for many DECT phones and other applications.Cordless bluetooth headsets are available, and often used with mobile telephones. Headsets are widely used for telephone-intensive jobs, in particular by call centre workers. They are also used by anyone wishing to hold telephone conversations with both hands free.
For older models of telephones, the headset microphone impedance is different from that of the original handset, requiring a telephone amplifier for the telephone headset. A telephone amplifier provides basic pin-alignment similar to a telephone headset adaptor, but it also offers sound amplification for the microphone as well as the loudspeakers.
Most models of telephone amplifiers offer volume control for loudspeaker as well as microphone, mute function and switching between headset and handset. Telephone amplifiers are powered by batteries or AC adaptors.
Ambient noise reduction
Among different types of headphones, in-ears are good at noise reduction. Interference from external sound can be reduced either by active noise cancellation, or by attenuating noise getting into the ear (passive noise cancellation). The two headphone types that do this attenuation best are in-ear canal headphones and closed-back headphones (both circumaural and supra aural).Open-back and earbud headphones provide some passive noise isolation as well, but to a much lesser extent than the closed-back and in-ear. Typically closed-back headphones block 8 to 12 dB and in-ears anywhere from 10 to 15 dB.
Transducer 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 the varying current of an audio signal is passed through the coil.
The alternating magnetic field produced by the current 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 moving-coil headphone drivers are derived from microphone capsule technology.
Electrostatic
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 driving the membrane, a sound wave is generated.
Electrostatic headphones are usually more expensive than moving-coil ones, and are comparatively uncommon. In addition, a special amplifier is required to amplify the signal to deflect the membrane, which often requires electrical potentials in the range of 100 to 1000 volts.
Due to the extremely thin and light diaphragm membrane, often only a few micrometers thick, and the complete absence of moving metalwork, the frequency response of electrostatic headphones usually extends well above the audible limit of approximately 20?kHz.
The high frequency response means that the low midband distortion level is maintained to the top of the audible frequency band, which is generally not the case with moving coil drivers.
Also, the frequency response peakiness regularly seen in the high frequency region with moving coil drivers is absent. The result is significantly better sound quality, if designed properly.
Electrostatic headphones are powered by anything from 100v to over 1kV, and are on the user's head. The usual method of making this safe is to limit the possible fault current to a low and safe value with resistors.
Electret
An electret driver functions along the same electromechanical means as an electrostatic driver. However the electret driver has a permanent charge built into it, where electrostatics have the charge applied to the driver by an external generator. Electret headphones, like electrostatics, are relatively uncommon. They are also typically cheaper and lower in technical capability and fidelity than electrostatics.Balanced armature
The JH Audio JH16 custom in-ear monitor utilizes 8 balanced armatures in a triple crossover configuration (4 low/2 mid/2 high). Multiple balanced armatures are often used to provide a higher fidelity sound. ?
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 there is electric current 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 military 'sound-powered' telephones. Some of these achieved astonishing electro-acoustic conversion efficiencies in the range 20% to 40% for narrow bandwidth voice signals.
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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 (e.g. below 20?Hz and above 16?kHz) 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. A few combine an armature driver with a small moving-coil driver for increased bass output.
Other transducer technologies
Transducer technologies employed much less commonly for headphones include the Heil Air Motion Transformer (AMT); Piezoelectric film; Ribbon planar magnetic; Magnetostriction and Plasma-ionisation.The first Heil AMT headphone was marketed by ESS Laboratories and was essentially an ESS AMT tweeter from one of the company's speakers being driven at full range. Since the turn of the century, only Precide of Switzerland have manufactured an AMT headphone.
Piezoelectric film headphones were first developed by Pioneer, their two models both used a flat sheet of film which limited the maximum volume of air that could be moved. Currently TakeT produce a piezoelectric film headphone which is shaped not unlike an AMT transducer but which like the driver Precide uses for their headphones, has a variation in the size of transducer folds over the diaphragm.
It additionally incorporates a two way design by its inclusion of a dedicated tweeter/supertweeter panel. The folded shape of a diaphragm allows a transducer with a larger surface area to fit within smaller space constraints.
This increases the total volume of air that can be moved on each excursion of the transducer given that radiating area.
Magnetostriction headphones, sometimes sold under the label of "Bonephones", are headphones that work via the transmission of vibrations against the side of head, transmitting the sound via bone conduction.
This is particularly helpful in situations where the ears must be left unobstructed or when used by those who are deaf for reasons which do not affect the nervous apparatus of hearing.
Magnetostriction headphones though, have greater limitations to their fidelity than conventional headphones which work via the normal workings of the ear.
Additionally, there was also one attempt to market a plasma-ionisation headphone in the early 1990s by a French company called Plasmasonics. It is believed that there are no functioning examples left.
Benefits and limitations
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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 fidelity greater than loudspeakers of similar cost. Part of their ability to do so comes from the lack of any need to perform room correction treatments with headphones.
High quality headphones 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 are also useful for video games that use 3D positional audio processing algorithms, as they allow players to better judge the position of an off-screen sound source (such as the footsteps of an opponent or their gun fire).
Although modern headphones have been particularly widely sold and used for listening to stereo recordings since the release of the Walkman, there is subjective debate regarding the nature of their reproduction of stereo sound.
Stereo recordings represent the position of horizontal depth cues (stereo separation) via volume and phase differences of the sound in question between the two channels. When the sounds from two speakers mix, they create the phase difference the brain uses to locate direction.
Through most headphones, because the right and left channels do not combine in this manner, the illusion of the phantom center can be perceived as lost. Hard panned sounds will also only be heard only in one ear rather than from one side.
Binaural recordings use a different microphone technique to encode direction directly as phase, with very little amplitude difference below 2?kHz, often using a dummy head, and can produce a surprisingly lifelike spatial impression through headphones.
Commercial recordings almost always use stereo, rather than binaural, recording, because loudspeaker listening has been more popular than headphone listening.
It is possible to change the spatial effects of stereo sound on headphones to better approximate the presentation of speaker reproduction 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).
Headsets can have ergonomic benefits over traditional telephone handsets. They allow call center agents to maintain better posture without needing to hand-hold a handset or tilt their head sideways to cradle it.
Dangers and volume solutions
Using headphones at a sufficiently high volume level may cause temporary or permanent hearing impairment or deafness. The headphone volume often has to compete with the background noise, especially in loud places such as subway stations, aircraft, and large crowds. Extended periods of exposure to high sound pressure levels created by headphones at high volume settings may be damaging; however, one hearing expert found that "fewer than 5% of users select volume levels and listen frequently enough to risk hearing loss."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.
The government of France 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 theoretically of immediate hearing loss, is 130dB).
Motorcycle and other power-sport riders benefit by wearing foam earplugs when legal to do so to avoid excessive road, engine, and wind noise, but their ability to hear music and intercom speech is enhanced when doing so. The ear can normally detect 1-billionth of an atmosphere of sound pressure level, hence it is incredibly sensitive.
At very high sound pressure levels, muscles in the ear tighten the tympanic membrane and this leads to a small change in the geometry of the ossicles and stirrup that results in lower transfer of force to the oval window of the inner ear (the acoustic reflex).
Listening to music through headphones while exercising can be dangerous. Blood may be diverted from the ears to the limbs leaving the inner ear more vulnerable to damage from loud sound.
A Finnish study recommended that exercisers should set their headphone volumes to half of their normal loudness and only use them for half an hour.
Source: http://planehealth.blogspot.com/2013/05/the-truth-about-ear-piece.html
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