View source for Headphones

{{Short description|Device put on or in the ears that plays sound}}
{{Other uses}}
{{pp-semi-indef}}
{{more citations needed|date=April 2017}}

[[File:Słuchawki referencyjne K-701 firmy AKG.jpg|thumb|Headphones on a stand]]

'''Headphones''' are a pair of small [[loudspeaker driver]]s worn on or around the head over a user's ears. They are [[electroacoustics (acoustical engineering)|electroacoustic]] [[transducer]]s, which convert an [[electrical signal]] to a corresponding sound. Headphones let a single user listen to an audio source privately, in contrast to a [[loudspeaker]], which emits sound into the open air for anyone nearby to hear. Headphones are also known as '''earphones'''<ref name=":5">{{cite web |url=http://www.merriam-webster.com/dictionary/earphone |title=earphone |access-date=4 January 2014 |url-status=live |archive-url=https://web.archive.org/web/20140119123425/http://www.merriam-webster.com/dictionary/earphone |archive-date=19 January 2014 }}</ref> or, [[colloquially]], '''cans'''.<ref>Stanley R. Alten ''Audio Basics'' Cengage 2011 {{ISBN|0-495-91356-1}} page&nbsp;63</ref> Circumaural (around the ear) and supra-aural (over the ear) headphones use a band over the top of the head to hold the drivers in place. Another type, known as '''earbuds''' or '''earpieces''',<ref name=":5" /> consists of individual units that plug into the user's [[ear canal]]; within that category have been developed cordless '''air buds''' using wireless technology. A third type are [[bone conduction]] headphones, which typically wrap around the back of the head and rest in front of the ear canal, leaving the ear canal open. In the context of [[telecommunication]], a [[Headset (audio)|headset]] is a combination of a headphone and [[microphone]].

Headphones connect to a signal source such as an audio [[amplifier]], [[radio]], [[CD player]], [[portable media player]], [[mobile phone]], [[video game console]], or [[electronic musical instrument]], either directly using a cord, or using [[wireless]] technology such as [[Bluetooth]], [[DECT]] or [[FM radio]]. The first headphones were developed in the late 19th century for use by [[switchboard operator]]s, to keep their hands free. Initially, the audio quality was mediocre and a step forward was the invention of [[high fidelity]] headphones.<ref>{{Cite web|url=http://www.stereocompare.com/headphones-buying-guide/#Hi%2520fidelity%2520headphones|title=Headphones : The Ultimate buying guide - Hi-fidelity headphones|website=StereoCompare|language=en-US|access-date=2016-03-03|url-status=live|archive-url=https://web.archive.org/web/20160307135117/http://www.stereocompare.com/headphones-buying-guide/#Hi%2520fidelity%2520headphones|archive-date=2016-03-07}}</ref><ref>{{Cite web |date=2022-06-20 |title=The Ultimate Headphones Buying Guide - Audio Inspects |url=https://audioinspects.com/headphones-buying-guide/ |access-date=2022-07-15 |language=en-US}}</ref>

Headphones exhibit a range of different audio reproduction quality capabilities. Headsets designed for telephone use typically cannot reproduce sound with the [[high fidelity]] of expensive units designed for music listening by [[audiophile]]s. Headphones that use cables typically have either a {{convert|1/4|in|mm}} or {{convert|1/8|in|mm}} [[phone jack]] for plugging the headphones into the audio source. Some headphones are wireless, using [[Bluetooth]] connectivity to receive the audio signal by radio waves from source devices like cellphones and digital players.<ref>{{cite web |url=https://www.fastcompany.com/3055208/its-true-apple-will-drop-the-headphone-jack-to-make-the-iphone-7-slimmer-and-simpler |title=It's True: Apple Will Drop Headphone Jack To Make The iPhone 7 Slimmer, Says Source |url-status=live |archive-url=https://web.archive.org/web/20160829052849/http://www.fastcompany.com/3055208/its-true-apple-will-drop-the-headphone-jack-to-make-the-iphone-7-slimmer-and-simpler |archive-date=2016-08-29 |work = Fast Company|first = Mark|last = Sullivan|date = 7 January 2016}}</ref> As a result of the [[Walkman effect]], beginning in the 1980s, headphones started to be used in public places such as sidewalks, grocery stores, and public transit.<ref>{{Cite web|url=https://www.independent.ie/entertainment/music/rewind-how-the-walkman-changed-the-world--26551309.html|title=Rewind: How the Walkman changed the world...|website=independent|date=15 July 2009 }}</ref> Headphones are also used by people in various professional contexts, such as [[audio engineer]]s mixing sound for live concerts or [[sound recording]]s and [[DJ]]s, who use headphones to [[cue (audio)|cue]] up the next song without the audience hearing, aircraft pilots and [[call center]] employees. The latter two types of employees use headphones with an integrated microphone.

== {{anchor|history}}History ==
[[File:Night_telephone_operator_1898.png|thumb|[[Switchboard operator|Telephone operator]] with a single head-mounted telephone-receiver (headphone), 1898]]

Headphones grew out of the need to free up a person's hands when operating a [[telephone]].<ref>{{Cite book |last=Prescott |first=George Bartlett |url=https://books.google.com/books?id=le0OAAAAYAAJ&pg=PA237 |title=Bell's Electric Speaking Telephone: Its Invention, Construction, Application, Modification, and History |date=1884 |publisher=D. Appleton |pages=137 |language=en |quote=The transmitter is placed on an upright rod at his right and the receiver is held constantly at his ear by means of a steel band passed over the head which band serves also as the magnet of the telephone He is therefore always in readiness to receive an order without the necessity of a preliminary call or signal and both his hands are left free to fill the orders. [Also see Figure 180]}}</ref> By the 1880s, soon after the [[invention of the telephone]], telephone [[switchboard operator]]s began to use head apparatuses to mount the [[telephone receiver]].<ref>{{Cite journal |url=http://archive.org/details/belltelephonemag13amerrich/page/248/ |title=The Telephone Problem in the World's Largest Metropolitan Area: A Summary of Past and Present |date=October 1934 |journal=Bell Telephone Magazine |publisher=[[American Telephone and Telegraph Company]] |others=Prelinger Library |volume=XIII |pages=248 |quote=Upper right image: A New York City central office in the '80s, showing "beehive" as well as early desk type switchboards, and both young women and boy operators [Note image of telephone operator's with head-mounted telephone receivers]}}</ref> The receiver was mounted on the head by a clamp which held it next to the ear.<ref>{{Cite book |last=Herbert |first=Thomas Ernest |url=https://books.google.com/books?id=i703AAAAMAAJ&pg=PA85 |title=The Telephone System of the British Post Office: A Practical Handbook |date=1898 |publisher=Page & Pratt |pages=85 |language=en |quote=Figure 73}}</ref> The head mount freed the switchboard operator's hands, so that they could easily connect the wires of the telephone callers and receivers.<ref name=":02">{{Cite magazine |url=https://books.google.com/books?id=4Hw3AQAAMAAJ&pg=PA194 |title=Some new Bell type switchboard accessories |date=November 1898 |magazine=Electrical Engineering and Telephone Magazine |volume=XII |pages=194 |language=en |quote=Figure 1}}</ref> The head-mounted telephone receiver in the singular form was called a ''headphone''.<ref name=":12">{{Cite journal |url=https://books.google.com/books?id=pjwiKBTJsQkC&pg=PA254 |title=Polk's Busy Test For Telephone Switchboards |date=November 21, 1894 |journal=Illustrated Electrical Review: A Journal of Scientific and Electrical Progress |publisher=Electrical Review Publishing Company |volume=25 |pages=251, 254 |language=en |quote=Referring to the illustrations on page 251, A is the switchboard, B is the inclined shelf usually employed in upright switchboards and C is the headphone.}}</ref><ref>{{Cite magazine |url=https://books.google.com/books?id=7y8-AQAAMAAJ&pg=PA401 |title=Behind the scenes at "Central" |date=October 1903 |magazine=The Book Lover's Magazine |publisher=Library Publishing Company |volume=II |pages=390–401 |language=en |quote=For the first week she does nothing but attach her headphone to an experienced operator's position and listen. [pp. 401]}}</ref> These head-mounted phone receivers, unlike modern headphones, only had one earpiece.<ref>{{Cite web |title=Head Clamp Receiver (c.1883) |url=http://waywiser.rc.fas.harvard.edu/objects/2935/headclamp-receiver;jsessionid=0737EFAE7F48A1A31244219DCED20682 |access-date=2023-05-06 |website=Collection of historical scientific instruments -- Harvard University |language=en}}</ref>

By the 1890s a listening device with two earpieces was developed by the British company [[Electrophone (information system)|Electrophone]]. The device created a listening system through the phone lines that allowed the customer to connect into live feeds of performances at theaters and opera houses across London. Subscribers to the service could listen to the performance through a pair of massive earphones that connected below the chin and were held by a long rod.<ref name="A Partial History of Headphones2">{{cite web |title=A Partial History of Headphones |url=https://www.smithsonianmag.com/arts-culture/a-partial-history-of-headphones-4693742/ |access-date=2020-12-27 |website=[[Smithsonian (magazine)|Smithsonian]] Magazine}}</ref>

French engineer Ernest Mercadier in 1891 patented a set of in-ear headphones.<ref>U.S. Patent No. 454,138 for "improvements in telephone-receivers...which shall be light enough to be carried while in use on the head of the operator."</ref><ref name="A Partial History of Headphones2" /> The German company [[Siemens Brothers]] at this time was also selling headpieces for telephone operators which had two earpieces, although placed outside the ear. The Siemens Brothers headpieces looked similar to modern headphones. The majority of headgear used by telephone operators continued to have only one earpiece.<ref>{{Cite book |last1=Preece |first1=Sir William Henry |url=https://books.google.com/books?id=WZ1RAAAAMAAJ&pg=PA56 |title=A Manual of Telephony |last2=Stubbs |first2=Arthur James |date=1893 |publisher=Whittaker and Company |pages=55–58 |language=en}}</ref>
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[[File:Interior_of_Fessenden_wireless_telegraph_station.png|thumb|left|[[Wireless telegraphy|Wireless telegrapher]] [[Reginald Fessenden]] with two head-mounted telephone-receivers (headphones), 1906]]
Headphones appeared in the emerging field of [[wireless telegraphy]], which was the [[History of broadcasting|beginning stage of radio broadcasting]]. Some early wireless telegraph developers chose to use the telephone receiver's [[Loudspeaker|speaker]] as the detector for the [[electrical signal]] of the wireless receiving circuit.<ref name=":2">{{Cite magazine |last=[[Archie Frederick Collins|Collins]] |first=Archie Frederick |url=https://books.google.com/books?id=euDmAAAAMAAJ&pg=PA285 |title=Review of wireless telegraph engineering practice |date=December 1902 |magazine=Telephony |publisher=Telephone Publishing Corporation |volume=4 |pages=279–288 |language=en}}</ref> By 1902 wireless telegraph innovators, such as [[Lee de Forest]], were using two jointly head-mounted telephone receivers to hear the signal of the receiving circuit.<ref>{{Cite magazine |url=https://books.google.com/books?id=fd_dEEq4SWAC&pg=PA181 |title=The De Forest Wireless Telegraph Station at Coney Island |date=July 1902 |magazine=Electrical Age |publisher=Electrical Age Publishing Company |volume=29 |pages=181 |language=en}}</ref> The two head-mounted telephone receivers were called in the singular form ''head telephones''.<ref name=":2" /> By 1908 the headpiece began to be written simply as ''head phones'',<ref>{{Cite book |last=Bullard |first=William Hannum Grubb |url=https://books.google.com/books?id=1upMAAAAMAAJ&pg=PA927 |title=Naval Electricians' Text Book |date=1908 |publisher=United States Naval Institute |pages=927 |language=en |quote=Listening in --. Keep the head phones on the head and at end of every sentence throw up listening key with fingers or thumb of right hand to assure yourself that the other party hears you clearly and answers you}}</ref> and a year later the compound word ''headphones'' began to be used.<ref>{{Cite magazine |last=McCaskey |first=E. L. |url=https://books.google.com/books?id=8X5IAAAAMAAJ&dq=%22headphones%22&pg=PA102 |title=Correspondence |date=May 22, 1909 |magazine=Modern Electrics |publisher=Modern electrics publication |volume=II |pages=102 |language=en |quote=My headphones are of the single pole type wound to the resistance of 3,000 ohms.}}</ref>
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[[File:Holtzer_Cabot_Wireless_Head_Normal_Receivers.png|thumb|[[Holtzer-Cabot]] telephone operator head receiver, wireless operator receiver, and telephone receiver, 1909]]
One of the earliest companies to make headphones for wireless operators was the [[Holtzer-Cabot|Holtzer-Cabot Company]] in 1909.<ref name=":3">{{Cite book |url=https://books.google.com/books?id=7Hs3AQAAMAAJ&pg=RA5-PA10 |title=Electrical Construction and Maintenance |date=April 1909 |publisher=McGraw-Hill Publishing Company |pages=10 |language=en}}</ref> They were also makers of head receivers for telephone operators and normal telephone receivers for the home.<ref name=":3" /> Another early manufacturer of headphones was Nathaniel Baldwin.<ref>{{Cite journal |last=Singer |first=Merril |date=1979 |title=Nathaniel Baldwin, Utah inventor and patron of the fundamentalist movement |url=https://issuu.com/utah10/docs/uhq_volume47_1979_number1/s/131081 |journal=Utah Historical Quarterly |volume=47 |issue=1|pages=42–53 |doi=10.2307/45060660 |jstor=45060660 |s2cid=254434880 }}</ref> He was the first major supplier of headsets to the [[U.S. Navy]].<ref>{{Cite book |last=Howeth |first=Linwood S. |url=https://books.google.com/books?id=sfI4i4znFmgC&pg=PA149 |title=History of Communications Electronics in the United States Navy |date=1963 |publisher=U.S. Government Printing Office |pages=148–149 |language=en}}</ref> In 1910, motivated by his inability to hear sermons during Sunday service, he invented a prototype telephone headset.<ref>{{Cite web |title=Great Falls Tribune 03 Jan 1930, page 7 |url=https://www.newspapers.com/image/238689831/ |access-date=2023-04-30 |website=Newspapers.com |language=en}}</ref> He offered it for testing to the navy, which promptly ordered 100 of them. Wireless Specialty Apparatus Co., in partnership with Baldwin Radio Company, set up a manufacturing facility in Utah to fulfill orders.<ref>{{Cite news |last=Heffernan |first=Virginia |date=2011-01-07 |title=Against Headphones |language=en-US |work=The New York Times |url=https://www.nytimes.com/2011/01/09/magazine/09FOB-medium-t.html |access-date=2023-05-06 |issn=0362-4331}}</ref> These early headphones used [[Moving iron speaker|moving iron drivers]],<ref name="hearthis"/> with either single-ended or balanced armatures. The common single-ended type used voice coils wound around the poles of a permanent magnet, which were positioned close to a flexible steel diaphragm. The audio current through the coils varied the magnetic field of the magnet, exerting a varying force on the diaphragm, causing it to vibrate, creating sound waves. The requirement for high sensitivity meant that no [[damping]] was used, so the [[frequency response]] of the diaphragm had large peaks due to resonance, resulting in poor [[sound quality]]. These early models lacked padding, and were often uncomfortable to wear for long periods. Their [[Electrical impedance|impedance]] varied; headphones used in [[telegraph]] and telephone work had an impedance of 75&nbsp;[[ohm]]s. Those used with early wireless radio had more turns of finer wire to increase sensitivity. Impedances of 1,000 to 2,000 ohms was common, which suited both crystal sets and [[triode]] receivers. Some very sensitive headphones, such as those manufactured by [[Kolster-Brandes|Brandes]] around 1919, were commonly used for early radio work.

In 1958, [[John C. Koss]], an [[audiophile]] and [[jazz musician]] from [[Milwaukee]], produced the first stereo headphones.<ref>{{cite web|title=Founded 1958 - World's First SP/3 Stereophone|url=https://www.koss.com/history/|website=koss.com|access-date=13 September 2017|url-status=live|archive-url=https://web.archive.org/web/20170913183148/https://www.koss.com/history/|archive-date=13 September 2017}}</ref><ref name="hearthis">{{cite news|title=Now hear this: the history of headphones|url=https://www.theguardian.com/business/2011/oct/30/history-of-headphones|last=Smith|first=Caspar|newspaper=The Guardian|date=30 October 2011|access-date=13 September 2017|url-status=live|archive-url=https://web.archive.org/web/20170913182953/https://www.theguardian.com/business/2011/oct/30/history-of-headphones|archive-date=13 September 2017}}</ref>

Smaller earbud-type earpieces, which plugged into the user's ear canal, were first developed for [[hearing aids]]. They became widely used with [[transistor radio]]s, which commercially appeared in 1954 with the introduction of the [[Regency TR-1]]. The most popular audio device in history, the transistor radio changed listening habits, allowing people to listen to the radio anywhere. The earbud uses either a moving iron driver or a [[crystal earpiece|piezoelectric crystal]] to produce sound. The 3.5&nbsp;mm radio and [[Phone connector (audio)|phone connector]], which is the most commonly used in portable applications today, has been used at least since the Sony EFM-117J transistor radio, which was released in 1964.<ref>{{cite web|title=Sony history 1960s|url=http://www.sony.net/Fun/design/history/1960.html|website=Sony official website|url-status=live|archive-url=https://web.archive.org/web/20160205195855/http://www.sony.net/Fun/design/history/1960.html|archive-date=2016-02-05}}</ref><ref>Description of 3.5mm earphone jack in described model: <br />{{cite web|url=http://www.worthpoint.com/worthopedia/vintage-sony-1960-efm-117j-radio-47603127|title=Vintage Sony 1960'S EFM-117J Radio|access-date=2016-01-25}}</ref> Its popularity was reinforced by its use on the [[Walkman]] portable tape player in 1979.

== Applications ==
[[File:Headphones-Sennheiser-HD555.jpg|thumb|[[Sennheiser]] HD 555 headphones, used in [[Sound recording and reproduction|audio production]] environments (2007)]]

[[File:Headset adaptor.jpg|thumb|This adaptor allowed an airline passenger to plug a standard 3.5mm stereo headphone into the twin mono jacks then common on airliners, avoiding the need to pay for a set of headphones from the airline]]

Wired headphones may be used with stationary [[Compact disc player|CD]] and [[DVD player]]s, [[home theater]], [[personal computer]]s, or portable devices (e.g., [[digital audio player]]/[[MP3 player]], [[mobile phone]]), as long as these devices are equipped with a headphone jack. [[Cordless]] headphones are not connected to their source by a cable. Instead, they receive a [[radio]] or [[infrared]] signal encoded using a radio or infrared transmission link, such as [[frequency modulation|FM]], [[Bluetooth]] or [[Wi-Fi]]. These are battery-powered receiver systems, of which the headphone is only a component. Cordless headphones are used with events such as a [[silent disco]].<!--[[User:Kvng/RTH]]-->

In the [[professional audio]] sector, headphones are used in live situations by [[disc jockey]]s with a [[DJ mixer]], and [[sound engineer]]s for monitoring signal sources. In radio studios, [[DJ]]s use a pair of headphones when talking to the microphone while the speakers are turned off to eliminate [[acoustic feedback]] while monitoring their own voice. In studio recordings, musicians and singers use headphones to play or sing along to a backing track or band. In military applications, audio signals of many varieties are monitored using headphones.

Wired headphones are attached to an audio source by a cable. The most common connectors are 6.35&nbsp;mm ({{frac|1|4}}{{nbsp}}inch) and 3.5&nbsp;mm [[Phone connector (audio)|phone connectors]]. The larger 6.35&nbsp;mm connector is more common on fixed location home or professional equipment. The 3.5&nbsp;mm connector remains the most widely used connector for portable application today. Adapters are available for converting between 6.35&nbsp;mm and 3.5&nbsp;mm devices.

[[File:Interrupteur.JPG|thumb|Headphone cord with integrated [[potentiometer]] for volume control]]
As active component, wireless headphones tend to be costlier due to the necessity for internal hardware such as a battery, a charging controller, a [[speaker driver]], and a wireless [[transceiver]], whereas wired headphones are a passive component, outsourcing speaker driving to the audio source.

Some headphone cords are equipped with a [[series circuit|serial]] [[potentiometer]] for volume control.

Wired headphones may be equipped with a non-detachable cable or a detachable auxiliary [[Gender of connectors and fasteners|male-to-male]] plug, as well as some with two ports to allow connecting another wired headphone in a [[parallel circuit]], which splits the audio signal to share with another participant, but can also be used to hear audio from two inputs simultaneously. An external audio splitter can retrofit this ability.<ref>{{cite web |last1=Arce |first1=Nicole |title=How To Use Two Or More Headphones On PC or Mac (Wired/Bluetooth) - Headphonesty |url=https://www.headphonesty.com/2020/07/use-two-headphones-pc-mac/ |access-date=29 May 2021 |date=2020-07-22}}</ref>

=== Applications for audiometric testing ===
Various types of specially designed headphones or earphones are also used to evaluate the status of the auditory system in the field of [[audiology]] for establishing hearing thresholds, medically diagnosing [[hearing loss]], identifying other hearing related disease, and monitoring hearing status in occupational [[hearing conservation program]]s.<ref>{{Cite book|url=https://www.worldcat.org/oclc/940449158|title=Hearing conservation manual|others=Hutchison, Thomas L., Schulz, Theresa Y., Council for Accreditation in Occupational Hearing Conservation.|isbn=978-0-9863038-0-7|edition=Fifth |date=2014|location=Milwaukee, WI|oclc=940449158}}</ref> Specific models of headphones have been adopted as the standard due to the ease of calibration and ability to compare results between testing facilities.<ref name=":0">{{Cite book|url=https://www.worldcat.org/oclc/877024342|title=Handbook of clinical audiology|others=Katz, Jack, Chasin, Marshall, English, Kristina M., 1951-, Hood, Linda J., Tillery, Kim L.|year=2015|isbn=978-1-4511-9163-9|edition=Seventh |location=Philadelphia|oclc=877024342}}</ref>

Supra-aural style headphones are historically the most commonly used in audiology as they are the easiest to calibrate and were considered the standard for many years. Commonly used models are the Telephonics Dynamic Headphone (TDH) 39, TDH-49, and TDH-50. In-the-ear or insert style earphones are used more commonly today as they provide higher levels of interaural attenuation, introduce less variability when testing 6,000 and 8,000&nbsp;Hz, and avoid testing issues resulting from collapsed ear canals. A commonly used model of insert earphone is the Etymotic Research ER-3A. Circum-aural earphones are also used to establish hearing thresholds in the extended high frequency range (8,000&nbsp;Hz to 20,000&nbsp;kHz). Along with Etymotic Research ER-2A insert earphones, the Sennheiser HDA300 and Koss HV/1A circum-aural earphones are the only models that have reference equivalent threshold sound pressure level values for the extended high frequency range as described by [[ANSI]] standards.<ref>{{Cite web|title=ANSI/ASA S3.6-2018 - Specification for Audiometers|url=https://webstore.ansi.org/Standards/ASA/ANSIASAS32018?source=preview|access-date=2020-11-13|website=webstore.ansi.org}}</ref><ref name=":0" /><ref>{{Cite web|title=ISO 389-2:1994|url=https://www.iso.org/cms/render/live/en/sites/isoorg/contents/data/standard/00/43/4378.html|access-date=2020-11-13|website=ISO|language=en}}</ref>

[[Audiometer]]s and headphones must be calibrated together. During the calibration process, the output signal from the audiometer to the headphones is measured with a [[sound level meter]] to ensure that the signal is accurate to the reading on the audiometer for [[sound pressure]] level and [[frequency]]. Calibration is done with the earphones in an [[acoustic coupler]] that is intended to mimic the transfer function of the outer ear. Because specific headphones are used in the initial audiometer calibration process, they cannot be replaced with any other set of headphones, even from the same make and model.<ref name=":0" />

== Electrical characteristics ==
[[Electrical characteristics of dynamic loudspeakers]] may be readily applied to headphones, because most headphones are small dynamic loudspeakers.

=== Impedance ===
Headphones are available with high or low [[Electrical impedance|impedance]] (typically measured at 1&nbsp;kHz). Low-impedance headphones are in the range 16 to 32&nbsp;ohms and high-impedance headphones are about 100–600&nbsp;ohms. As the impedance of a pair of headphones increases, more voltage (at a given current) is required to drive it, and the loudness of the headphones for a given voltage decreases. In recent years, impedance of newer headphones has generally decreased to accommodate lower voltages available on battery powered [[CMOS]]-based portable electronics. This has resulted in headphones that can be more efficiently driven by battery-powered electronics. Consequently, newer amplifiers are based on designs with relatively low output impedance.

The impedance of headphones is of concern because of the output limitations of amplifiers. A modern pair of headphones is driven by an amplifier, with lower impedance headphones presenting a larger load. Amplifiers are not ideal; they also have some output impedance that limits the amount of power they can provide. To ensure an even frequency response, adequate [[damping factor]], and undistorted sound, an amplifier should have an output impedance less than 1/8 that of the headphones it is driving (and ideally, as low as possible). If output impedance is large compared to the impedance of the headphones, significantly higher distortion is present.<ref>{{cite web |last=Siau |first=John |title=The "0-Ohm" Headphone Amplifier |url=http://www.benchmarkmedia.com/discuss/sites/default/files/Headphone-Amplifier-Performance-Part-2.pdf |access-date=26 June 2012 |url-status=live |archive-url=https://web.archive.org/web/20130210012625/http://www.benchmarkmedia.com/discuss/sites/default/files/Headphone-Amplifier-Performance-Part-2.pdf |archive-date=10 February 2013 }}</ref> Therefore, lower impedance headphones tend to be louder and more efficient, but also demand a more capable amplifier. Higher impedance headphones are more tolerant of amplifier limitations, but produce less volume for a given output level.

Historically, many headphones had relatively high impedance, often over 500&nbsp;ohms so they could operate well with high-impedance [[Valve amplifier#Operation|tube amplifiers]]. In contrast, modern transistor amplifiers can have very low output impedance, enabling lower-impedance headphones. This means that older audio amplifiers or stereos often produce poor-quality output on some modern, low-impedance headphones. In this case, an external [[headphone amplifier]] may be beneficial.

=== Sensitivity ===
Sensitivity is a measure of how effectively an earpiece converts an incoming electrical signal into an audible sound. It thus indicates how loud the headphones are for a given electrical drive level. It can be measured in [[decibel]]s of [[sound pressure]] level per milli[[watt]] (dB (SPL)/mW) or decibels of sound pressure level per [[volt]] (dB (SPL) / V).<ref>{{cite web |url= http://gilmore2.chem.northwestern.edu/tech/dbohn1_tech.htm |title=Understanding Headphone Power Requirements |url-status=dead |archive-url=https://web.archive.org/web/20110608015203/http://gilmore2.chem.northwestern.edu/tech/dbohn1_tech.htm |archive-date=2011-06-08 |work = HeadWize|publisher = Northwestern University|first = Dennis|last = Bohn}}</ref>  Both definitions are widely used, often interchangeably. As the output voltage (but not power) of a headphone amplifier is essentially constant for most common headphones, dB/mW is often more useful if converted into dB/V using [[Ohm's law]]:

:<math>\mathrm{dB (SPL)}/\mathrm{V} = \mathrm{dB (SPL)}/\mathrm{mW} - 10 \cdot \log_{10}{\frac{\mathrm{Impedance}}{1000}}</math>

Once the sensitivity per volt is known, the maximum volume for a pair of headphones can be easily calculated from the maximum amplifier output voltage. For example, for a headphone with a sensitivity of 100&nbsp;dB (SPL)/V, an amplifier with an output of 1 [[root mean square]] (RMS) [[voltage]] produces a maximum volume of 100&nbsp;dB.

Pairing high-sensitivity headphones with power amplifiers can produce dangerously high volumes and damage headphones. The maximum [[sound pressure]] level is a matter of preference, with some sources recommending no higher than 110 to 120&nbsp;dB. In contrast, the American [[Occupational Safety and Health Administration]] recommends an average SPL of no more than 85&nbsp;dB(A) to avoid long-term hearing loss, while the [[European Union]] standard EN 50332-1:2013 recommends that volumes above 85&nbsp;dB(A) include a warning, with an absolute maximum volume (defined using 40–4,000&nbsp;Hz noise) of no more than 100&nbsp;dB to avoid accidental hearing damage.<ref>{{cite web |title= BS EN 50332 tests for headphones and earphones with portable music players|work = ISVR Consulting|url=http://www.isvr.co.uk/labtests/en50332.htm |archive-url=https://web.archive.org/web/20180821031842/https://www.isvr.co.uk/labtests/en50332.htm |date = 2 August 2018 |archive-date=2018-08-21}}</ref>  Using this standard, headphones with sensitivities of 90, 100 and 110&nbsp;dB (SPL)/V should be driven by an amplifier capable of no more than 3.162, 1.0 and 0.3162 RMS volts at maximum volume setting, respectively to reduce the risk of hearing damage.

The sensitivity of headphones is usually between about 80 and 125&nbsp;dB/mW and usually measured at 1&nbsp;kHz.<ref>{{cite web |title=Understanding Earphone/Headphone Specifications |url=http://shure.custhelp.com/app/answers/detail/a_id/2991/~/understanding-earphone-%2F-headphone-specifications |archive-url=https://web.archive.org/web/20160618042652/http://shure.custhelp.com/app/answers/detail/a_id/2991/~/understanding-earphone-%2F-headphone-specifications |archive-date=2016-06-18 |work=Shure Customer Help |publisher=Shure}}</ref>

== Specifications ==
Headphone size can affect the balance between fidelity and portability. Generally, headphone form factors can be divided into four separate categories: ''circumaural (over-ear)'', ''supra-aural (on-ear)'', ''earbud'' and ''in-ear''.

=== Connectivity ===

==== Wired ====
Wired headphones make a direct electrical connection to the source device using a cable, typically connected with a [[headphone jack]].

==== Wireless ====
Modern wireless or cordless earphones have no cord connecting the two earphones to the source device or to each other; they receive audio by means of a wireless technology such as [[Bluetooth]]. In historical usage, 'wireless' referred to a connection to a radio receiver, which was known as a wireless.

On some models both audio streams are transmitted to one earphone which forwards one stream to the other earphone. On other models each earphone receives its audio stream directly from the source device. The former arrangement has the advantage of being compatible with legacy systems while the latter arrangement has the advantage of causing less power drain in the earphone that has to forward one audio stream. 

Connection between the two earphones also being wireless may be referred to as '''true wireless stereo (TWS)''', offering longer battery life and complete transmission on left and right channels, avoiding possible source signal omission if only one is worn. <ref name=tws>{{cite press release |url= https://www.telink-semi.com/introduction-true-wireless-stereo/ |title= An Introduction to True Wireless Stereo (TWS) Technology |work = Telink Semiconductor |date = 19 Aug 2020| author = Telink Staff |url-status=live |archive-url= https://web.archive.org/web/20240118124336/https://www.telink-semi.com/introduction-true-wireless-stereo/ |archive-date=2024-01-18 }}</ref>

=== Ear adaption ===

==== Circumaural ====
[[Image:Headphones 1.jpg|thumb|Circumaural headphones have large pads that surround the outer ear.]]
''Circumaural headphones'' (sometimes called ''full size headphones'' or ''over-ear 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 {{convert|500|g|lb|0}}. Ergonomic headband and earpad design is required to reduce discomfort resulting from weight. These are commonly used by drummers in recording.

==== Supra-aural ====
[[Image:GradoPrestige-HeadphoneArticle.jpg|thumb|A pair of supra-aural (on-ear) headphones]]
''Supra-aural headphones'' or ''on-ear headphones'' have pads that press against the ears, rather than around them. They were commonly bundled with [[personal stereo]]s 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.

==== Ear-fitting headphones ====

===== Earphones =====
{{Redirect|Earphone}}
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Earphones are very small headphones that are fitted directly in the [[outer ear]], facing but not inserted in the ear canal. Earphones are portable and convenient, but many people consider them uncomfortable.<ref name=timebuds>{{cite news|url=http://www.time.com/time/magazine/article/0,9171,1982314,00.html|title=Custom-Made Headphones: Listen Up Before It's Too Late|date=26 April 2010|work=[[Time (magazine)|Time]] |access-date= 21 July 2015|first=Peter|last=Ha|url-status=dead|archive-url=https://web.archive.org/web/20130817093143/http://www.time.com/time/magazine/article/0,9171,1982314,00.html |archive-date=17 August 2013}}</ref>{{fv|reason=Talks about earbuds, not earphones|date=November 2023}} 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]].<ref name=timebuds/><ref>{{cite journal|url=http://www.ear-hearing.com/pt/re/earhearing/abstract.00003446-200412000-00001.htm |title= Output Levels of Commercially Available Portable Compact Disc Players and the Potential Risk to Hearing|volume=25|issue=6|pages=513–27|journal= Ear and Hearing|access-date= 21 July 2015|date=December 2004|last1=Fligor|first1=Brian J.|last2=Cox|first2=L. Clarke|doi=10.1097/00003446-200412000-00001|pmid=15604913|s2cid= 11043107}}</ref> On the other hand, they let the user be better aware of their surroundings. Since the early days of the [[transistor radio]], earphones have commonly been bundled with personal music devices. They are sold at times with foam or rubber pads for comfort. (The use of the term ''earbuds'', which has been around since at least 1984, did not hit its peak until after 2001, with the success of Apple's MP3 player.<ref>{{cite web |url=https://mobile.nytimes.com/2014/05/18/magazine/who-made-that-earbud.html |title=Who Made That Earbud? |work = The New York Times Magazine|date = 16 May 2014|first = Daniel|last = Engber|url-status=live |archive-url= https://web.archive.org/web/20170202030114/https://mobile.nytimes.com/2014/05/18/magazine/who-made-that-earbud.html |archive-date=2017-02-02 }}</ref>)

===== In-ear headphones =====
{{Main|In-ear monitor}}
[[Image:InEarMonitors.jpg|thumb|upright|In-ear monitors extend into the ear canal, providing isolation from outside noise.]]
In-ear headphones, also known as ''in-ear monitors (IEMs)'' or ''canalphones'', are small headphones with similar portability to earbuds that are inserted in the [[ear canal]] itself. IEMs are higher-quality in-ear headphones and are used by [[audio engineer]]s and [[musician]]s as well as audiophiles.

The outer shells of in-ear headphones are made up of a variety of materials, such as plastic, [[aluminum]], ceramic and other metal alloys. Because in-ear headphones engage the ear canal, they can be prone to sliding out, and they block out much environmental noise. Lack of sound from the environment can be a problem when sound is a necessary cue for safety or other reasons, as when walking, driving, or riding near or in vehicular traffic.<ref name=RoSPA>{{cite web|title=Headphones as a Driving Distraction|url=https://www.rospa.com/rospaweb/docs/advice-services/road-safety/drivers/headphones-as-a-driver-distraction.pdf|publisher=The Royal Society for the Prevention of Accidents|access-date=14 September 2017|url-status=live|archive-url=https://web.archive.org/web/20170915023105/https://www.rospa.com/rospaweb/docs/advice-services/road-safety/drivers/headphones-as-a-driver-distraction.pdf|archive-date=15 September 2017}}</ref> Some in-ear headphones utilize built-in microphones to allow some outside sound to be heard when desired.<ref>{{Cite web|title=Use Ambient sound on your Samsung earbuds|url=https://www.samsung.com/us/support/answer/ANS00078084/|access-date=2021-08-13|website=Samsung Electronics America|language=en-US}}</ref><ref>{{Cite web|title=WF-1000XM3 {{!}} Help Guide {{!}} Listening to ambient sound during music playback (Ambient Sound Mode)|url=https://helpguide.sony.net/mdr/wf1000xm3/v1/en/contents/TP0002289887.html|access-date=2021-08-13|website=helpguide.sony.net}}</ref>

Generic or custom-fitting ear canal plugs are made from [[silicone]] rubber, [[elastomer]], or foam. Such plugs in lower-end devices may be interchangeable, which increases the risk of them falling off and getting lodged in the ear canal. Custom in-ear headphones use castings of the ear canal to create custom-molded plugs that provide added comfort and noise isolation.<ref name="timebuds" />

Some wireless earphones include a charging case.

=== Open- or closed-back ===
Both circumaural and supra-aural headphones can be further differentiated by the type of earcups:

; {{vanchor|Open-back}}
: Headphones having 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, due to including sounds from the environment.

; {{vanchor|Semi-open}}
: They have a design that can be considered as a compromise between open-back headphones and closed-back headphones. Some{{Who|date=July 2015}} believe the term "semi-open" is purely there for marketing purposes. There is no exact definition for the term semi-open headphone. Where the open-back approach has hardly any measure to block sound at the outer side of the diaphragm and the closed-back approach really has a closed chamber at the outer side of the diaphragm, a semi-open headphone can have a chamber to partially block sound while letting some sound through via openings or vents.

; {{vanchor|Closed-back}}
: Closed-back (or sealed) styles have the back of the earcups closed. They usually block some of the ambient noise. Closed-back headphones usually can produce stronger low frequencies than open-back headphones.

=== Headset ===
{{Main|Headset (audio)}}
[[File:Plantronics headset.jpg|thumb|A typical example of a headset used for [[voice chat]]s]]

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.

==== Telephone headsets ====
[[File:Se bluetooth headset.jpg|thumb|left|[[Sony Ericsson]] Cordless bluetooth headset]]
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 2.5&nbsp;mm jack sockets for many DECT phones and other applications. Cordless [[bluetooth]] headsets are available, and often used with [[mobile telephone]]s. 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 [[electrical impedance|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 [[amplifier|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 adaptor]]s.

==== Communication headsets ====
[[File:Communication Headset.jpg|thumb|upright=.8|Aviation headset<ref>{{cite web|title=Lightspeed Aviation 30 3G Discontinued Aviation Headset|url=https://www.lightspeedaviation.com/product/thirty-3g/|website=lightspeedaviation.com|access-date=26 Dec 2020}}</ref>]]
Communication headsets are used for two-way communication and typically consist of a headphone and attached microphone. Such headsets are used in a variety of professions as aviation, military, sports, music, and many service-oriented sectors. They come in all shapes and sizes, depending on use, required noise attenuation, and fidelity of communication needed.

== Ambient noise reduction ==
Unwanted sound from the environment can be reduced by excluding sound from the ear by passive noise isolation, or, often in conjunction with isolation, by active [[Noise-cancelling headphones|noise cancellation]].
[[File:In-ears-earphones.png|thumb|left|In-ears are among those good for noise isolation.]]
Passive noise isolation is essentially using the body of the earphone, either over or in the ear, as a passive earplug that simply blocks out sound. The headphone types that provide most attenuation are in-ear canal headphones and closed-back headphones, both circumaural and supra aural. Open-back and earbud headphones provide some passive noise isolation, but much less than the others. Typical closed-back headphones block 8 to 12&nbsp;dB, and in-ears anywhere from 10 to 15&nbsp;dB. Some models have been specifically designed for drummers to facilitate the drummer monitoring the recorded sound while reducing sound directly from the drums as much as possible. Such headphones claim to reduce ambient noise by around 25&nbsp;dB.

Active [[noise-cancelling headphones]] use a microphone, amplifier, and speaker to pick up, amplify, and play ambient noise in phase-reversed form; this to some extent cancels out unwanted noise from the environment without affecting the desired sound source, which is not picked up and reversed by the microphone. They require a power source, usually a battery, to drive their circuitry. Active noise cancelling headphones can attenuate ambient noise by 20&nbsp;dB or more, but the active circuitry is mainly effective on constant sounds and at lower frequencies, rather than sharp sounds and voices. Some noise cancelling headphones are designed mainly to reduce low-frequency engine and travel noise in aircraft, trains, and automobiles, and are less effective in environments with other types of noise.

== Transducer technology ==
Headphones use various types of [[transducer]] to convert electrical signals to sound.

=== Moving-coil ===
[[Image:Headphone-transducer.jpg|thumb|right|A typical moving-coil headphone transducer]]
The [[Loudspeaker|moving coil driver]], more commonly referred to as a "dynamic" driver is the most common type used in headphones. It consists of a stationary [[magnet]] element affixed to the frame of the headphone, which sets up a static magnetic field. The magnet in headphones is typically composed of [[Ferrite (magnet)|ferrite]] or [[Neodymium magnet|neodymium]]. A [[voice coil]], a light coil of wire, is suspended in the magnetic field of the magnet, attached to a diaphragm, typically fabricated from lightweight, high-stiffness-to-mass-ratio cellulose, polymer, carbon material, paper or the like.   When the varying current of an [[audio signal]] is passed through the coil, it creates a varying magnetic field that reacts against the static magnetic field, exerting a varying force on the coil causing it and the attached diaphragm to vibrate. The vibrating diaphragm pushes on the air to produce [[sound wave]]s.

=== Electrostatic ===
[[Image:Es spk.gif|thumb|right|Electrostatic loudspeaker diagram]]
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 1,000&nbsp;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&nbsp;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. Well-designed electrostatic headphones can produce significantly better sound quality than other types.{{citation needed|reason=Such broad claims need sources|date=May 2015}}

Electrostatic headphones require a voltage source generating 100&nbsp;V to over 1&nbsp;kV, and are on the user's head. Since the invention of insulators, there is no actual danger. They do not need to deliver significant [[electric current]], which further limits the electrical hazard to the wearer in case of fault.

=== 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 and electrostatic headphones are relatively uncommon. Original electrets were also typically cheaper and lower in technical capability and fidelity than electrostatics. Patent applications from 2009 to 2013 have been approved that show by using different materials, i.e. a "Fluorinated cyclic olefin electret film", Frequency response chart readings can reach 50&nbsp;kHz at 100 db. When these new improved electrets are combined with a traditional dome headphone driver, headphones can be produced that are recognised by the Japan Audio Society as worthy of joining the Hi Res Audio program. US patents 8,559,660 B2. 7,732,547 B2.7,879,446 B2.7,498,699 B2.

=== Planar magnetic ===
Planar magnetic (also known as orthodynamic) headphones use similar technology to electrostatic headphones, with some fundamental differences. They operate similarly to [[Loudspeaker#Ribbon and planar magnetic loudspeakers|planar magnetic loudspeakers]].

A planar magnetic driver consists of a relatively large membrane that contains an embedded wire pattern. This membrane is suspended between two sets of permanent, oppositely aligned, magnets. A current passed through the wires embedded in the membrane produces a magnetic field that reacts with the field of the permanent magnets to induce movement in the membrane, which produces sound.

=== Balanced armature ===
{{multiple image
 | header            = Balanced armature transducer
 | image1            = Bal Arm.JPG
 | caption1          = Armature balanced and exerting no force on diaphragm
 | image2            = Bal Arm1.JPG
 | caption2          = Armature torqued and exerting a force on diaphragm
}}

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 left 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 right diagram, when there is [[electric current]] through the coil, it [[Electromagnet|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 (acoustics)|diaphragm]] to make [[sound]].

[[Image:JH16 Balanced Armatures.jpg|upright|thumb|A custom in-ear monitor which uses 8 balanced armatures in a triple crossover configuration (4 low/2 mid/2 high). Headphone designs often use multiple balanced armatures to provide a higher fidelity 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.{{Clarify|date=January 2014|reason=isn't more sound from less power the definition of high efficiency?}} 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 telephone]]s. Some of these achieved astonishing electro-acoustic conversion efficiencies, in the range of 20% to 40%, for narrow bandwidth voice signals.

Today they are typically used only in in-ear headphones and hearing aids, where their high efficiency and diminutive size is a major advantage.<ref>{{Cite web|url=https://www.innerfidelity.com/content/how-balanced-armature-receiversdrivers-work|title=How Balanced Armature Receivers/Drivers Work|last=Hertsens|first=Tyll |date=2014-12-15|website=InnerFidelity|language=en|archive-url=https://web.archive.org/web/20150914044126/http://www.innerfidelity.com/content/how-balanced-armature-receiversdrivers-work |archive-date=2015-09-14|url-status=live}}</ref> They generally are limited at the extremes of the hearing spectrum (e.g. below 20&nbsp;Hz and above 16&nbsp;kHz) and require a better seal 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.

The earliest loudspeakers for radio receivers used balanced armature drivers for their cones.<ref>{{Cite book|url=https://books.google.com/books?id=5IMSAQAAMAAJ&q=earliest+loudspeakers+used+balanced+armature+drivers+for+their+cones.|title=A History of Engineering and Science in the Bell System: The early years (1875-1925)|last1=Joel|first1=Amos E.|date=1975|publisher=The Laboratories|isbn=9780608080666|language=en}}</ref>

=== Thermoacoustic technology ===
The thermoacoustic effect generates sound from the audio frequency Joule heating of the conductor, an effect that is not magnetic and does not vibrate the speaker.
In 2013 a carbon nanotube thin-yarn earphone based on the thermoacoustic mechanism was demonstrated by a research group in Tsinghua University.<ref>{{cite journal |author1=Yang Wei |author2=Xiaoyang Lin |author3=Kaili Jiang |author4=Peng Liu |author5=Qunqing Li |author6=Shoushan Fan |title=Thermoacoustic Chips with Carbon Nanotube Thin Yarn Arrays. |journal=Nano Letters |year=2013 |doi=10.1021/nl402408j |pmid=24041369 |volume=13 |issue=10 |pages=4795–801|bibcode=2013NanoL..13.4795W }}</ref> The as-produced CNT thin yarn earphone has a working element called CNT thin yarn thermoacoustic chip. Such a chip is composed of a layer of CNT thin yarn array supported by the silicon wafer, and periodic grooves with certain depth are made on the wafer by micro-fabrication methods to suppress the heat leakage from the CNT yarn to the substrate.{{citation needed|date=May 2015}}

=== Other transducer technologies ===
Transducer technologies employed much less commonly for headphones include the [[Oskar Heil|Heil]] [[Air Motion Transformer]] (AMT); Piezoelectric film; Ribbon planar magnetic; Magnetostriction and [[Plasma speaker|Plasma or Ionic]]. The first [[Air Motion Transformer|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 used a flat sheet of film that limited the maximum volume of air movement. Currently, TakeT produces a piezoelectric film headphone shaped similarly to an AMT transducer but, which like the Precide driver, 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 ''Bonephones'', work by vibrating against the side of head, transmitting sound via [[bone conduction]]. This is particularly helpful in situations where the ears must be unobstructed, or for people who are [[deaf]] for reasons that do not affect the nervous apparatus of [[hearing]]. Magnetostriction headphones though, are limited in their fidelity compared to conventional headphones that rely on the normal workings of the ear. Additionally, in the mid-1980s, a French company called Audio Reference tried to market the Plasmasonic plasma headphone invented by Henri Bondar.<ref>{{cite magazine| date = March 1984 | title = Plasmasonic | page = 100 | magazine = La Nouvelle Revue Du Son| location = FR}}</ref><ref>{{cite patent| country = US| number = 4460809A| title = Process and device for converting a periodic LF electric voltage into sound waves | inventor = Henri Bondar}}</ref> There are no known functioning examples left. Due to the small volume of air in a headphone, the plasma or ionic transducer can become a full range driver although the high temperatures and voltages needed makes them very rare.

== Benefits and limitations ==
[[File:Sony MDR-7506 Stowed 7617.jpg|thumb|Sony MDR-7506 headphones in stowed configuration]]
[[File:Micro amplifier (booster) FIIO Fujiyama for smartphone etc. headphones.jpg|thumb|A micro audio amplifier for boosting the output power of [[smartphone]]s etc. to headphones. Used for example to compensate a built-in volume limit in smartphones, the higher volume levels could, however, lead to ear damage.]]

Headphones can prevent other people from hearing the sound, either for [[privacy]] or to prevent disturbing others, 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&nbsp;Hz within 3&nbsp;dB. While a loudspeaker must use a relatively large (often 15" or 18") [[speaker driver]] to reproduce low frequencies, headphones can accurately reproduce bass and sub-bass frequencies with speaker drivers only 40-50 millimeters wide (or much smaller, as is the case with [[in-ear monitor]] headphones). Headphones' impressive low-frequency performance is possible because they are so much closer to the ear that they only need to move relatively small volumes of air.

Marketed claims such as 'frequency response 4&nbsp;Hz to 20&nbsp;kHz' are usually overstatements; the product's response at frequencies lower than 20&nbsp;Hz is typically very small.<ref>{{cite web|url = http://reviews.cnet.com/4520-7612_7-6322607-4.html|website =CNET|title = How to buy headphones|url-status = live|archive-url=https://web.archive.org/web/20110820010315/http://reviews.cnet.com/4520-7612_7-6322607-4.html |archive-date=2011-08-20 |quote =Even the flimsiest, cheap headphones routinely boast extremely low bass-response performance—15 or 20Hz—but almost always sound lightweight and bright.}}</ref>
Headphones are also useful for [[video game]]s 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 gunfire).

Although modern headphones have been particularly widely sold and used for listening to [[Stereophonic sound|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 (waves)|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 [[Panning (audio)|panned]] sounds are also heard only in one ear rather than from one side.

[[Binaural recording]]s use a different microphone technique to encode direction directly as phase, with very little amplitude difference below 2&nbsp;kHz, often using a [[dummy head recording|dummy head]]. They can produce a surprisingly lifelike spatial impression through headphones. Commercial recordings almost always use stereo recording, rather than binaural, because loudspeaker listening is more common 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.

Headsets can have [[ergonomic]] benefits over traditional telephone handsets. They allow [[call center]] agents to maintain better [[human position|posture]] without needing to hand-hold a [[transceiver#Telephony|handset]] or tilt their head sideways to cradle it.<ref>[http://www.osha.gov/SLTC/etools/computerworkstations/checklist.html United States Department of Labor. Occupational Safety & Health Administration. ''Computer Workstation. Checklist.''] {{webarchive|url=https://web.archive.org/web/20090202190631/http://osha.gov/SLTC/etools/computerworkstations/checklist.html |date=2009-02-02 }} Accessed February 2, 2009.</ref>

== Health and safety ==
{{See also|Automatic volume limiter}}

=== Dangers and risks ===
[[File:Consumer Reports - product testing - headphones in anechoic chamber.tif|thumb|Product testing - headphones in an [[anechoic chamber]]]]
Using headphones at a sufficiently high [[loudness|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 to hearing;<ref>{{cite web|url=http://www.asha.org/public/hearing/disorders/causes_adults.htm|title=Causes of Hearing Loss in Adults|work=asha.org|access-date=21 July 2015|archive-url=https://web.archive.org/web/20101213224226/http://asha.org/public/hearing/disorders/causes_adults.htm|archive-date=13 December 2010|url-status=dead}}</ref><ref>{{cite web|url=http://www.nidcd.nih.gov/health/hearing/noise.asp|title=Noise-Induced Hearing Loss|work=nih.gov|archive-url=https://web.archive.org/web/20160509092930/https://www.nidcd.nih.gov/health/hearing/noise.asp|archive-date=9 May 2016|url-status=dead|access-date=21 July 2015}}</ref> Nearly 50% of teenagers and young adults (12 to 35 years old) in middle and high income countries listen to unsafe levels of sound on their personal audio devices and smartphones.<ref>{{Cite web|url=https://www.who.int/pbd/deafness/activities/MLS/en/|archive-url=https://web.archive.org/web/20150227041628/http://www.who.int/pbd/deafness/activities/MLS/en/|url-status=dead|archive-date=February 27, 2015|title=1.1 billion people at risk of hearing loss|last=World Health Organization|date=15 Mar 2018|access-date=2 Feb 2019}}</ref> However, one hearing expert found in 2012 (before the worldwide adoption of smartphones as the main personal listening devices) that "fewer than 5% of users select volume levels and listen frequently enough to risk hearing loss."<ref>{{cite web|url=http://www.audiologyonline.com/articles/article_detail.asp?article_id=221|title=Five Myths in Assessing the Effects of Noise on Hearing|author=William W. Clark|work=AudiologyOnline|archive-url=https://web.archive.org/web/20120924203231/http://www.audiologyonline.com/articles/article_detail.asp?article_id=221|archive-date=24 September 2012|url-status=live|access-date=21 July 2015}}</ref> [[International Telecommunication Union|The International Telecommunication Union]] recently published "Guidelines for safe listening devices/systems" recommended that sound exposure not exceed 80 [[decibel]]s, [[A-weighted]] dB(A) for a maximum of 40 hours per week.<ref>{{Cite web|url=https://www.itu.int/rec/T-REC-H.870-201808-I/en|title=H.870 : Guidelines for safe listening devices/systems|website=www.itu.int|access-date=2019-02-28}}</ref> The [[European Union]] have also set a similar limit for users of personal listening devices (80&nbsp;dB(A) for no more than 40 hours per week) and for each additional increase of 3-dB in sound exposure, the duration should be cut in half (83&nbsp;dB(A) for no more than 20 hours, 86&nbsp;dB(A) for 10 hours per week, 89&nbsp;dB(A) for 5 hours per week and so on. Most major manufactures of smartphones now include some safety or volume limiting features and warning messaging in their devices.<ref>{{Cite web|url=https://www.apple.com/sound/|title=Sound and Hearing|website=Apple|language=en-us|access-date=2019-02-28}}</ref><ref>{{Cite web|url=https://www.samsung.com/us/support/troubleshooting/TSG01001429/|title=Limit Media Volume|website=Samsung Electronics America|language=en|access-date=2019-02-28}}</ref> though such practices have received mixed response from some segments of the buying who favor the personal choice of setting their own volume levels.

The usual way of limiting sound volume on devices driving headphones is by limiting output power. This has the additional undesirable effect of being dependent of the efficiency of the headphones; a device producing the maximum allowed power may not produce adequate volume when paired with low-efficiency, high-impedance equipment, while the same amount of power can reach dangerous levels with very efficient earphones.

Some studies have found that people are more likely to raise volumes to unsafe levels while performing strenuous exercise.<ref>{{cite web|url=http://www.healthyhearing.com/content/faqs/Hearing-loss/Causes/31070-Loud-noise-during-exercise|title=Can Loud Noise during Exercise Damage my Hearing?|website=Healthy Hearing|location=Item 4|archive-url=https://web.archive.org/web/20141109002409/http://www.healthyhearing.com/content/faqs/Hearing-loss/Causes/31070-Loud-noise-during-exercise|archive-date=9 November 2014|url-status=live|access-date=8 November 2014}}</ref> A Finnish study<ref>Airo, Erkko; J. Pekkarinen; P. Olkinuora. "Listening to music with earphones: an assessment of noise exposure," ''Acustica–Acta Acustica'', pp.&nbsp;82, 885–894. (1996)</ref> recommended that exercisers should set their headphone volumes to half of their normal loudness and only use them for half an hour.

Other than hearing risk, there is a general danger that listening to loud music in headphones can distract the listener and lead to injury and accidents.<ref>{{cite web|url=https://abcnews.go.com/Health/w_DietAndFitnessNews/deaf-danger-perils-earbuds-exercising/story?id=13925714#.UcMJhufVDoI|title=Deaf to Danger: The Perils of Earbuds|last1=Greenfield|first1=Paige|date=25 June 2011|website=ABC News|archive-url=https://web.archive.org/web/20131214122323/https://abcnews.go.com/Health/w_DietAndFitnessNews/deaf-danger-perils-earbuds-exercising/story?id=13925714#.UcMJhufVDoI|archive-date=14 December 2013|url-status=live|access-date=20 June 2013}}</ref><ref>{{cite journal |last1=Lichenstein |first1=R |last2=Smith |first2=DC |last3=Ambrose |first3=JL |last4=Moody |first4=LA |title=Headphone use and pedestrian injury and death in the United States: 2004-2011. |journal=Injury Prevention |date=October 2012 |volume=18 |issue=5 |pages=287–90 |doi=10.1136/injuryprev-2011-040161 |pmid=22248915|s2cid=25177965 }}</ref> [[Noise-cancelling headphones]] add extra risk. Several countries and states have made it illegal to wear headphones while driving or cycling.<ref name=RoSPA/>

There have also been numerous reports of [[contact dermatitis]] due to exposure to in-ear headphones such as Apple [[AirPods]].<ref name=":1">{{Cite journal |last1=Hayakawa |first1=Michitaro |last2=Suzuki |first2=Chihiro |last3=Zhu |first3=Yingyao |last4=Anzai |first4=Hidemi |date=April 2022 |title=Allergic contact dermatitis to gold in the parts of in-ear headphones |url=https://onlinelibrary.wiley.com/doi/10.1111/cod.14036 |journal=Contact Dermatitis |language=en |volume=86 |issue=4 |pages=328–330 |doi=10.1111/cod.14036 |pmid=34978717 |s2cid=245651803 |issn=0105-1873}}</ref><ref>{{Cite journal |last1=Chan |first1=Justin |last2=Rabi |first2=Sina |last3=Adler |first3=Brandon L. |date=November 2021 |title=Allergic Contact Dermatitis to (Meth)Acrylates in Apple AirPods Headphones |url=https://journals.lww.com/10.1097/DER.0000000000000735 |journal=Dermatitis |language=en |volume=32 |issue=6 |pages=e111–e112 |doi=10.1097/DER.0000000000000735 |pmid=34807535 |s2cid=233923350 |issn=2162-5220}}</ref> The contact dermatitis would be caused by in-ear headphones that contain gold, rubber, dyes, acrylates, or methacrylates.<ref name=":1" /> However, there have been no studies done to prove that exposure to in-ear headphones will cause contact dermatitis, rather that there is a correlation between in-ear headphone use and contact dermatitis cases.<ref name=":1" />

=== Occupational health and safety ===
Hearing risk from headphones' use also applies to workers who must wear electronic or communication headsets as part of their daily job (i.e., [[pilot]]s, [[call center]] and dispatch operators, [[sound engineer]]s [[Firefighter|, firefighters]], etc.) and hearing damage depends on the exposure time. The National Institute for Occupational Safety and Health ([[NIOSH]]) recommends sound exposure not exceed 85&nbsp;dB(A) over 8 hour work day as a time-weighted average.<ref>{{Cite journal|date=June 1998 |title=Occupational noise exposure; criteria for a recommended standard |url=https://www.cdc.gov/niosh/docs/98-126/default.html |publisher=National Institute for Occupational Safety and Health |website=CDC |language=en-us|doi=10.26616/NIOSHPUB98126|doi-access=free}}</ref> NIOSH uses the 3-dB exchange rate often referred to as "time-intensity tradeoff" which means if sound exposure level is increased by 3 decibels, the duration of exposure should be cut in half. NIOSH published several documents targeted at protecting the hearing of workers who must wear communication headsets such as call center operators,<ref>{{Cite journal|date=September 2011 |title=Reducing Noise Hazards for Call & Dispatch Center Operators |url=https://www.cdc.gov/niosh/docs/wp-solutions/2011-210/default.html |publisher=National Institute for Occupational Safety and Health |website=CDC |language=en-us|doi=10.26616/NIOSHPUB2011210|doi-access=free}}</ref> firefighters,<ref>{{Cite journal|date=May 2013 |title=Promoting Hearing Health among Firefighters |url=https://www.cdc.gov/niosh/docs/wp-solutions/2013-142/default.html |publisher=National Institute for Occupational Safety and Health |website=CDC |language=en-us|doi=10.26616/NIOSHPUB2013142|doi-access=free}}</ref> and musicians and sound engineers.<ref>{{Cite journal|date=June 2015  |publisher=National Institute for Occupational Safety and Health |website=CDC |title=Reducing the risk of hearing disorders among musicians.|url=https://www.cdc.gov/niosh/docs/wp-solutions/2015-184/default.html|language=en-us|doi=10.26616/NIOSHPUB2015184|doi-access=free}}</ref><ref>{{Cite journal|last1=McGinnity|first1=Siobhan|last2=Beach|first2=Elizabeth Francis|last3=Cowan|first3=Robert S. C.|last4=Mulder|first4=Johannes|date=2020-10-22|title=The hearing health of live-music sound engineers|url=https://pubmed.ncbi.nlm.nih.gov/33089760|journal=Archives of Environmental & Occupational Health|volume=76|issue=6|pages=301–312|doi=10.1080/19338244.2020.1828241|issn=2154-4700|pmid=33089760|bibcode=2021ArEOH..76..301M |s2cid=224821849}}</ref>

== See also ==
* [[Bone conduction]]
* [[Digital audio player]]
* [[Earmuffs]]
* [[Headphone amplifier]]
* [[In-ear monitor]]
* [[Loudspeaker]]
* [[Noise-cancelling headphones]]

== References ==
{{Reflist}}

== External links ==
* {{Commons category-inline|Headphones}}
* {{Wiktionary-inline|headphone|earphone|earpiece|stereophone|canalphones|earbud}}
* [[wikt:earpad|Earpad]]

{{Music technology}}

{{Authority control}}

[[Category:Headphones| ]]
[[Category:Headgear|Phones]]
[[Category:Audio engineering]]
[[Category:Consumer electronics]]
[[Category:Loudspeakers]]
[[Category:Transducers]]
[[Category:Audiovisual introductions in 1910]]
[[Category:Audiology]]