Headphones are a pair of small
loudspeakerA loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
s, or less commonly a single speaker, held close to a user's
earThe ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....
s and connected to a signal source such as an audio
amplifierGenerally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
,
radioRadio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
, CD player or
portable Media PlayerA portable media player or digital audio player, is a consumer electronics device that is capable of storing and playing digital media such as audio, images, video, documents, etc. the data is typically stored on a hard drive, microdrive, or flash memory. In contrast, analog portable audio...
. They are also known as
stereophones,
headsets or, colloquially,
cans. The in-ear versions are known as
earphones or
earbuds. In the context of
telecommunicationTelecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
, the term headset is used to describe a combination of headphone and
microphoneA microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...
used for
two-way communicationTwo-way communication - uses communication to negotiate with the public, resolve conflict, and promote mutual understanding and respect between the organization and its public. Two-Way Communication in Public Relations...
, for example with a
telephoneThe telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...
.
History
The telephone earpiece, such as the one pictured at the right, was common at the beginning of the 20th century. Headphones originated from the earpiece, and were the only way to listen to electrical audio signals before amplifiers were developed. The first truly successful set was developed by
Nathaniel BaldwinNathaniel Baldwin was the inventor of headphones and a supporter of the early Mormon fundamentalist movement.- Biography :...
, who made them by hand in his kitchen and sold them to the U.S. Navy.
Very sensitive headphones such as those manufactured by Brandes around 1919 were commonly used for early radio work. These early headphones used
moving iron driversThe earliest loudspeakers for speech and music were moving iron speakers. These are still used today in some miniature speakers where small size and low cost count, and sound quality is unimportant. A moving iron speaker consists of a ferrous metal diaphragm or reed, and a permanent magnet. The...
, either single ended or balanced armature. The requirement for high sensitivity meant no damping was used, thus the sound quality was crude. They also had very poor comfort compared to modern types, usually having no padding and too often having excessive clamping force to the head. Their
impedanceElectrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...
varied; headphones used in telegraph and telephone work had an impedance of 75 ohms. Those used with early wireless radio had to be more sensitive and were made with more turns of finer wire; impedance of 1,000 to 2,000 ohms was common, which suited both crystal sets and triode receivers.
In early powered radios, the headphone was part of the
vacuum tubeIn electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
's
plateA plate is a type of electrode that formed part of a vacuum tube. The plate is impressed with a positive charge so that it may capture and flow electrons within a circuit....
circuit and had dangerous voltages on it. It was normally connected directly to the positive high voltage battery terminal, and the other battery terminal was securely earthed. The use of bare electrical connections meant that users could be shocked if they touched the bare headphone connections while adjusting an uncomfortable headset.
Applications
Headphones may be used both with fixed equipment such as
CDA Compact Disc player , or CD player, is an electronic device that plays audio Compact Discs. CD players are often a part of home stereo systems, car audio systems, and personal computers. They are also manufactured as portable devices...
or
DVD playerA DVD player is a device that plays discs produced under both the DVD-Video and DVD-Audio technical standards, two different and incompatible standards. These devices were invented in 1997 and continue to thrive...
s,
home theaterHome cinema, also commonly called home theater, are home entertainment set-ups that seek to reproduce a movie theater experience and mood with the help of video and audio equipment in a private home....
,
personal computerA personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
s and with portable devices (e.g. digital audio player/mp3 player,
mobile phoneA mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...
, etc.).
CordlessThe term cordless literally means without a cord and is generally used to refer to electrical or electronic devices that are powered by a battery or battery pack and can operate without a power cord or cable attached to a fixed electricity supply such as an outlet, generator, or other centralized...
headphones are not connected via a wire, receiving a
radioRadio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
or
infraredInfrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
signal encoded using a radio or infrared transmission link, like
FMIn telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
,
BluetoothBluetooth is a proprietary open wireless technology standard for exchanging data over short distances from fixed and mobile devices, creating personal area networks with high levels of security...
or
Wi-FiWi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...
. These are actually made of powered receiver systems of which the headphone is only a component, these types of cordless headphones are being used more frequently with events such as a
Silent discoSilent disco has become a common name for a disco where people dance to music listened to on wireless headphones. Rather than using a speaker system, music is broadcast via an FM-transmitter with the signal being picked up by wireless headphone receivers worn by the participants. Those without the...
or Silent Gig.
In the
professional audioProfessional audio, also 'pro audio', refers to both an activity and a type of audio equipment. Typically it encompasses the production or reproduction of sound for an audience, by individuals who do such work as an occupation like live event support, using sound reinforcement systems designed for...
sector headphones are used in live situations by
disc jockeyA disc jockey, also known as DJ, is a person who selects and plays recorded music for an audience. Originally, "disc" referred to phonograph records, not the later Compact Discs. Today, the term includes all forms of music playback, no matter the medium.There are several types of disc jockeys...
s with a
DJ mixerA DJ mixer is a type of audio mixing console used by disc jockeys.The key features that differentiate a DJ mixer from other types of audio mixers are the ability to redirect a non-playing source to headphones and the presence of a crossfader, which allows for an easier transition between two sources...
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. In the military, audio signals of many varieties are monitored using headphones.
Wired headphones are attached to an audio source. The most common connection standards are 6.35mm (¼″) and 3.5mm
TRS connectorA TRS connector is a common family of connector typically used for analog signals including audio. It is cylindrical in shape, typically with three contacts, although sometimes with two or four . It is also called an audio jack, phone jack, phone plug, and jack plug...
s and
socketsIn electronics and electrical assemblies, the term jack commonly refers to a surface-mounted connector, often, but not always, with the female electrical contact or socket, and is the "more fixed" connector of a connector pair...
. The larger 6.35mm connector tending to be found on fixed location home or professional equipment.
Sony, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
introduced the smaller, and now widely used, 3.5mm "minijack" stereo connector in 1979, adapting the older
monophonicMonaural or monophonic sound reproduction is single-channel. Typically there is only one microphone, one loudspeaker, or channels are fed from a common signal path...
3.5mm connector for use with its
WalkmanWalkman is a Sony brand tradename originally used for portable audio cassette, and now used to market Sony's portable audio and video players as well as a line of Sony Ericsson mobile phones...
portable stereo tape player and the 3.5mm connector remains the common connector for portable application today. Adapters are available for converting between 6.35mm and 3.5mm devices.
Electrical characteristics
Electrical characteristics of dynamic loudspeakers may be readily applied to headphones since most headphones are small dynamic loudspeakers.
Impedance
Headphones are available with low or high impedance measured at 1 kHz. Low-impedance headphones are in the range 75 to 150 ohms and high impedance headphones are about 600 ohms. High impedance headphones have been popular among tube amplifier aficionados, and in classroom or studio situations requiring many headphones connected in parallel to the same source. Low impedance headphones yield a louder sound from a standard headphone jack, and require less voltage to achieve a target sound pressure level—an important consideration for portable electronics.
Sensitivity
SensitivityStimulus|Sensitivity may refer to:* Sensitivity , the ability to react to a stimulus* Sensitivity , the strength of physical or emotional reaction in people* Sensitivity , variations in process dynamics and control systems...
is a measure of a
transducerA transducer is a device that converts one type of energy to another. Energy types include electrical, mechanical, electromagnetic , chemical, acoustic or thermal energy. While the term transducer commonly implies the use of a sensor/detector, any device which converts energy can be considered a...
's output when driven with a specific reference input. Headphone manufacturers often loosely use the term "efficiency" where sensitivity should be used. Headphone
efficiencyEnergy conversion efficiency is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The useful output may be electric power, mechanical work, or heat.-Overview:...
(power in/power out)
is a type of sensitivity, but efficiency is usually not an important characteristic to measure for headphones (see Efficiency vs Sensitivity).
Common "units" for headphone sensitivity are "dB/mW" and "dB/mV". This notation is an inappropriate simplification, but what these mean are dB SPL (sound pressure level) measured in a standard ear for a 1 kHz sinusoidal headphone input of either 1 milli
wattThe watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
or one milli
voltThe volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
. Technical notation would be "dB ref. 20μPa/mW" or "dB ref. 20μPa/mV". One can convert between these two references if the impedance is known.
Types of headphones
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 any intrusive external noise. Because of their size, circumaural headphones can be heavy and there are some sets which weigh over 500 grams (1 lb). Good headband and earpad design is required to reduce discomfort resulting from weight.
Supra-aural
Supra-aural headphones have pads that sit on top of the ears, rather than around them. They were commonly bundled with
personal stereoThe personal stereo is the term given to a portable audio player using an audiocassette player. This allows the listening of music through headphones while a person is mobile. The first personal stereo was the Stereobelt invented and patented by Andreas Pavel in 1977. Pavel attempted to...
s during the 1980s. This type of headphone generally tends to be smaller and more lightweight than circumaural headphones, resulting in less attenuation of outside noise.
Open or closed back
Circumaural and supra-aural headphones can both also 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 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.
Earbuds
Among audio professionals,
earbuds and
earphones refer to very small headphones that are fitted directly in the
outer earThe outer ear is the external portion of the ear, which consists of the pinna, concha, and external auditory meatus. It gathers sound energy and focuses it on the eardrum . One consequence of the configuration of the external ear is to selectively boost the sound pressure 30- to 100-fold for...
, 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-Definition:Deafness is the inability for the ear to interpret certain or all frequencies of sound.-Environmental Situations:Deafness can be caused by environmental situations such as noise, trauma, or other ear defections...
. From about 1990 earbuds have commonly been bundled with personal music devices.
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
musicianA musician is an artist who plays a musical instrument. It may or may not be the person's profession. Musicians can be classified by their roles in performing music and writing music.Also....* A person who makes music a profession....
s 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
Silicones are inert, synthetic compounds with a variety of forms and uses. Typically heat-resistant and rubber-like, they are used in sealants, adhesives, lubricants, medical applications , cookware, and insulation....
rubber, elastomerAn elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...
, 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. 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
A headset is a headphone combined with a
microphoneA microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...
. Headsets provide the equivalent functionality of a telephone handset with hands-free operation. The most common uses for headsets are in aviation, on theatre/television studio intercom systems, in console or PC gaming,
call centreA call centre or call center is a centralised office used for the purpose of receiving and transmitting a large volume of requests by telephone. A call centre is operated by a company to administer incoming product support or information inquiries from consumers. Outgoing calls for telemarketing,...
s and other telephone-intensive jobs and also for personal use at the computer to facilitate comfortable simultaneous conversation and typing. 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.
Telephone headsets
Telephone headsets connect to a fixed-line telephone system. A telephone headset functions by replacing the
handsetOn a telephone, the handset is a device the user holds to the ear to hear the audio sound. Modern-day handsets usually contain the phone's microphone as well, but in early telephones the microphone was mounted directly on the telephone itself, which often was attached to a wall at a convenient...
of a telephone. All telephone headsets come in a standard 4P4C commonly called an RJ-9 connector.
For older models of telephones, the headset microphone
impedanceElectrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...
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
amplificationGenerally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
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 headset/handset switching. Telephone amplifiers are powered by batteries or AC adaptors.
Ambient noise reduction
Interference from external sound can be reduced either by active noise cancellation, or by attentuating noise getting into the ear. The two headphone types that do this best are in-ear canal headphones and closed-back headphones (both circumaural and supraural). Open-back and earbud headphones provide some 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.
Technology
Headphone transducers employ one or more of several methods of sound reproduction.
Moving-coil
The
moving coil driverA loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
, more commonly referred to as a "dynamic" driver is the most common type used in headphones. The operating principle consists of a stationary
magnetA magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...
ic element affixed to the frame of the headphone which sets up a static magnetic field. The magnetic element in headphones is typically composed of
ferriteFerrites are chemical compounds consisting of ceramic materials with iron oxide as their principal component. Many of them are magnetic materials and they are used to make permanent magnets, ferrite cores for transformers, and in various other applications.Many ferrites are spinels with the...
or
neodymiumA neodymium magnet , the most widely-used type of rare-earth magnet, is a permanent magnet made from an alloy of neodymium, iron, and boron to form the Nd2Fe14B tetragonal crystalline structure. Developed in 1982 by General Motors and Sumitomo Special Metals, neodymium magnets are the strongest...
. 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 coilA voice coil is the coil of wire attached to the apex of a loudspeaker cone. It provides the motive force to the cone by the reaction of a magnetic field to the current passing through it...
, when an audio current 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
soundSound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
. Modern moving-coil headphone drivers are derived from
microphoneA microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...
capsule technology.
Electrostatic
Electrostatic drivers consist of a thin, electrically charged diaphragm, typically a coated
PET filmBoPET is a polyester film made from stretched polyethylene terephthalate and is used for its high tensile strength, chemical and dimensional stability, transparency, reflectivity, gas and aroma barrier properties and electrical insulation.A variety of companies manufacture boPET and other...
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 in proximity to a 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, whereas 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
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 currentElectric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
through the coil, it
magnetizesAn electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off...
the armature one way or the other, causing it to rotate slightly one way or the other about the pivot thus moving the
diaphragmIn the field of acoustics, a diaphragm is a transducer intended to faithfully inter-convert mechanical motion and sound. It is commonly constructed of a thin membrane or sheet of various materials. The varying air pressure of the sound waves imparts vibrations onto the diaphragm which can then be...
to make
soundSound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
.
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.
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
HeilOskar Heil was a German electrical engineer and inventor. He studied physics, chemistry, mathematics, and music at the Georg-August University of Göttingen and was awarded his PhD in 1933, for his work on molecular spectroscopy.-Personal life:At the Georg-August University in Göttingen, Oskar Heil...
Air Motion TransformerThe Air Motion Transformer is a loudspeaker mechanism, or audio transducer, invented by Dr. Oskar Heil. It operates on a different principle than both electrodynamic and electrostatic speaker drivers...
(AMT); Piezoelectric film; Ribbon planar magnetic; Magnetostriction and
Plasma-ionisationPlasma speakers are a form of loudspeaker which varies air pressure via a high-energy electrical plasma instead of a solid diaphram. Connected to the output of an audio amplifier, plasma speakers vary the size of a plasma glow discharge, corona discharge or electric arc which then acts as a...
. The first
Heil AMTThe Air Motion Transformer is a loudspeaker mechanism, or audio transducer, invented by Dr. Oskar Heil. It operates on a different principle than both electrodynamic and electrostatic speaker drivers...
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
PrecidePrecide is a Swiss company that makes high-end audio equipment. Precide is one of the few companies in the high end audio market who use Air Motion Transformer or AMT drivers in their products. They are one of only two companies ever to use this driver to produce a headphone and are the only...
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.
MagnetostrictionMagnetostriction is a property of ferromagnetic materials that causes them to change their shape or dimensions during the process of magnetization. The variation of material's magnetization due to the applied magnetic field changes the magnetostrictive strain until reaching its saturation value, λ...
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 conductionBone conduction is the conduction of sound to the inner ear through the bones of the skull.Bone conduction is the reason why a person's voice sounds different to him/her when it is recorded and played back. Because the skull conducts lower frequencies better than air, people perceive their own...
. 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
hearingHearing is the ability to perceive sound by detecting vibrations through an organ such as the ear. It is one of the traditional five senses...
. 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
Headphones may be used to prevent other people from hearing the sound either for
privacyPrivacy is the ability of an individual or group to seclude themselves or information about themselves and thereby reveal themselves selectively...
or to prevent disturbance, as in listening in a public
libraryIn a traditional sense, a library is a large collection of books, and can refer to the place in which the collection is housed. Today, the term can refer to any collection, including digital sources, resources, and services...
. 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).
Although modern headphones have been particularly widely sold and used for listening to
stereo recordingsThe term Stereophonic, commonly called stereo, sound refers to any method of sound reproduction in which an attempt is made to create an illusion of directionality and audible perspective...
since the release of the
WalkmanWalkman is a Sony brand tradename originally used for portable audio cassette, and now used to market Sony's portable audio and video players as well as a line of Sony Ericsson mobile phones...
, 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
phasePhase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.-Formula:The phase of an oscillation or wave refers to a sinusoidal function such as the following:...
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
pannedPanning is the spread of a sound signal into a new stereo or multi-channel sound field. A typical physical recording console pan control is a knob with a pointer which can be placed from the 8 o'clock dial position fully left to the 4 o'clock position fully right...
sounds will also only be heard only in one ear rather than from one side.
Binaural recordingBinaural recording is a method of recording sound that uses two microphones, arranged with the intent to create a 3-D stereo sound sensation for the listener of actually being in the room with the performers or instruments. This effect is often created using a technique known as "Dummy head...
s use a different microphone technique to encode direction directly as phase, with very little amplitude difference below 2 kHz, often using a
dummy headIn acoustics, dummy head recording is a method used to make binaural recordings, that allow a listener wearing headphones to perceive the directionality and the room acoustics of single or multiple sources.Human perception of the direction of a sound source is complex, and consists of:#Simple...
, and can produce a surprisingly life-like 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
BlumleinAlan Dower Blumlein was a British electronics engineer, notable for his many inventions in telecommunications, sound recording, stereo, television and radar...
shuffler (a custom EQ employed to augment the low-frequency content of the difference information in a stereo signal). While cross-feed can reduce the unpleasantness that some listeners find with hard panned stereo in headphones, a
dummy headIn acoustics, dummy head recording is a method used to make binaural recordings, that allow a listener wearing headphones to perceive the directionality and the room acoustics of single or multiple sources.Human perception of the direction of a sound source is complex, and consists of:#Simple...
recording with artificial pinnae, played through headphones, can give the experience of hearing the performance as though situated in the position of the dummy head. Optimal sound is achieved when the dummy head matches the listener's head, since pinnae vary greatly in size and shape.
Headsets can have ergonomic benefits over traditional telephone handsets. They allow
call centerA call centre or call center is a centralised office used for the purpose of receiving and transmitting a large volume of requests by telephone. A call centre is operated by a company to administer incoming product support or information inquiries from consumers. Outgoing calls for telemarketing,...
agents to maintain better
postureHuman positions refers to the different positions that the human body can take.There are several synonyms that refer to the human position, often used interchangeably, but having specific flavors....
without needing to hand-hold a handset or tilt their head sideways to cradle it.
Over time, headphone cables fail, usually by copper wires breaking at junction points on the cord (at the TRS jack, or at the point of connection to the headphone) after repeated flexing. These sites are usually fitted with some kind of strain relief, but eventually fail.
Dangers and volume solutions
Using headphones at a sufficiently high
volumeVolume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
level may cause temporary or permanent
hearing impairment-Definition:Deafness is the inability for the ear to interpret certain or all frequencies of sound.-Environmental Situations:Deafness can be caused by environmental situations such as noise, trauma, or other ear defections...
or deafness due to an effect called "masking." The headphone volume has to compete with the
background noiseIn acoustics and specifically in acoustical engineering, background noise or ambient noise is any sound other than the sound being monitored. Background noise is a form of noise pollution or interference. Background noise is an important concept in setting noise regulations...
, especially in excessively loud places such as subway stations, aircraft, and large crowds. Extended periods of the excessively loud volume 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
FranceThe French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan 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).
Other risks arise from the reduced awareness of external sounds—some
jurisdictionJurisdiction is the practical authority granted to a formally constituted legal body or to a political leader to deal with and make pronouncements on legal matters and, by implication, to administer justice within a defined area of responsibility...
s regulate the use of headphones while
drivingDriving is the controlled operation and movement of a land vehicle, such as a car, truck or bus.Although direct operation of a bicycle and a mounted animal are commonly referred to as riding, such operators are legally considered drivers and are required to obey the rules of the road...
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 theft, particularly in busy environments where bumping into another person would be ignored, e.g., metro stations.
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
intercomAn intercom , talkback or doorphone is a stand-alone voice communications system for use within a building or small collection of buildings, functioning independently of the public telephone network. Intercoms are generally mounted permanently in buildings and vehicles...
speech is actually 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. Since earplugs reduce the noise in the auditory canal, this protective mechanism is less likely to trigger, and full sensitivity of the ear is maintained. This technique allows excellent hearing of speech, music and most external sounds at sustainable levels without hearing damage.
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 a half hour.
See also
- Cushion
A cushion is a soft bag of some ornamental material, stuffed with wool, hair, feathers, polyester staple fiber, non-woven material, or even paper torn into fragments. It may be used for sitting or kneeling upon, or to soften the hardness or angularity of a chair or couch...
- Bone conduction
Bone conduction is the conduction of sound to the inner ear through the bones of the skull.Bone conduction is the reason why a person's voice sounds different to him/her when it is recorded and played back. Because the skull conducts lower frequencies better than air, people perceive their own...
- Digital audio player
- Headphone amplifier
A headphone amplifier is an audio amplifier designed particularly to drive headphones instead of loudspeakers. Most commonly they are found embedded in electronic devices such as integrated amplifiers, portable music players and televisions, but standalone units are not uncommon.-Consumer headphone...
- In-ear monitor
In-ear monitors are devices used by musicians, audio engineers and audiophiles to listen to music or to hear a custom crafted mix of vocals and stage instrumentation for live performance or recording studio mixing...
- Noise-cancelling headphone
Noise-cancelling headphones reduce unwanted ambient sounds by means of active noise control . This involves using one or more microphones placed near the ear, and electronic circuitry which uses the microphone signal to generate an "antinoise" signal...
- earpad
External links
Headphone resources