Editing Microphone (section)

== Varieties ==
{{More citations needed section|date=April 2023}}

Microphones are categorized by their transducer principle (condenser, dynamic, etc.) and by their directional characteristics (omni, cardioid, etc.). Sometimes other characteristics such as diaphragm size, intended use or orientation of the principal sound input to the principal axis (end- or side-address) of the microphone are used to describe the microphone.

=== Condenser <span class="anchor" id="Condenser microphone"></span>===
<!--"Condenser microphone", "Consensor microphone", "Condenser mic" redirect here.-->
[[File:Oktava319-internal.jpg|thumb|upright|Inside the Oktava 319 condenser microphone]]
[[File:Condenser microphone.svg|thumb|Inner workings of the condenser microphone]]

The '''condenser microphone''', invented at Western Electric in 1916 by E. C. Wente,<ref>{{cite web |url=http://www.stokowski.org/Development_of_Electrical_Recording.htm |title=Bell Laboratories and The Development of Electrical Recording |website=Stokowski.org (Leopold Stokowski site) |archive-url=https://web.archive.org/web/20230621223522/http://www.stokowski.org/Development_of_Electrical_Recording.htm |archive-date=June 21, 2023 }}</ref> is also called a '''capacitor microphone''' or '''electrostatic microphone'''—capacitors were historically called condensers. The diaphragm acts as one plate of a capacitor, and audio vibrations produce changes in the distance between the plates. Because the capacitance of the plates is inversely proportional to the distance between them, the vibrations produce changes in capacitance. These changes in capacitance are used to measure the [[audio signal]].<ref>{{cite encyclopedia |title=Electromechanical Transducer |url=https://www.britannica.com/technology/electromechanical-transducer |encyclopedia=Britannica |access-date=June 2, 2024 }}</ref> The assembly of fixed and movable plates is called an ''element'' or ''capsule''.

Condenser microphones span the range from telephone mouthpieces through inexpensive karaoke microphones to high-fidelity recording microphones. They generally produce a high-quality audio signal and are now the popular choice in laboratory and [[recording studio]] applications. The inherent suitability of this technology is due to the very small mass that must be moved by the incident sound wave compared to other microphone types that require the sound wave to do more work.

Condenser microphones require a power source, provided either via microphone inputs on equipment as [[phantom power]] or from a small battery. Power is necessary for establishing the capacitor plate voltage and is also needed to power the microphone electronics. Condenser microphones are also available with two diaphragms that can be electrically connected to provide a range of [[#Microphone polar patterns|polar patterns]], such as cardioid, omnidirectional, and figure-eight. It is also possible to vary the pattern continuously with some microphones, for example, the [[Røde]] NT2000 or CAD M179.

There are two main categories of condenser microphones, depending on the method of extracting the audio signal from the transducer: DC-biased microphones, and radio frequency (RF) or high frequency (HF) condenser microphones.

==== DC-biased condenser ====
With a '''DC-biased condenser microphone''', the plates are [[Voltage bias|biased]] with a fixed charge (''Q''). The [[voltage]] maintained across the capacitor plates changes with the vibrations in the air, according to the capacitance equation (C = {{fract|Q|V}}), where Q = charge in [[coulomb]]s, C = capacitance in [[farad]]s and V = potential difference in [[volt]]s. A nearly constant charge is maintained on the capacitor. As the capacitance changes, the charge across the capacitor does change very slightly, but at audible frequencies it is sensibly constant. The capacitance of the capsule (around 5 to 100&nbsp;[[Farad|pF]]) and the value of the bias resistor (100&nbsp;[[Ohm|MΩ]] to tens of GΩ) form a filter that is high-pass for the audio signal, and low-pass for the bias voltage. Note that the time constant of an [[RC circuit]] equals the product of the resistance and capacitance.

Within the time frame of the capacitance change (as much as 50&nbsp;ms at 20&nbsp;Hz audio signal), the charge is practically constant and the voltage across the capacitor changes instantaneously to reflect the change in capacitance. The voltage across the capacitor varies above and below the bias voltage. The voltage difference between the bias and the capacitor is seen across the series resistor. The voltage across the resistor is amplified for performance or recording. In most cases, the electronics in the microphone itself contribute no voltage gain as the voltage differential is quite significant, up to several volts for high sound levels.

==== RF condenser ====
[[File:AKG C451B.jpg|thumb|[[AKG Acoustics|AKG]] C451B small-diaphragm condenser microphone]]

'''RF condenser microphones''' use a comparatively low RF voltage, generated by a low-noise oscillator. The signal from the oscillator may either be amplitude modulated by the capacitance changes produced by the sound waves moving the capsule diaphragm, or the capsule may be part of a [[resonant circuit]] that modulates the frequency of the oscillator signal. Demodulation yields a low-noise audio frequency signal with a very low source impedance. The absence of a high bias voltage permits the use of a diaphragm with looser tension, which may be used to achieve wider frequency response due to higher compliance. The RF biasing process results in a lower electrical impedance capsule, a useful by-product of which is that RF condenser microphones can be operated in damp weather conditions that could create problems in DC-biased microphones with contaminated insulating surfaces. The [[Sennheiser]] MKH series of microphones use the RF biasing technique. A covert, remotely energized application of the same physical principle called [[The Thing (listening device)|the Thing]] was devised by Soviet Russian inventor [[Leon Theremin]] and used to bug the US Ambassador's residence in Moscow between 1945 and 1952.

==== Electret condenser ====
{{Main|Electret microphone}}
[[File:US Patent 3118022 - Gerhard M. Sessler James E. West - Bell labs - electroacustic transducer - foil electret condenser microphone 1962 1964 - pages 1-3.png|thumb|left|First patent on foil electret microphone by G. M. Sessler et al. (pages 1 to 3)]]

An electret microphone is a type of condenser microphone invented by [[Gerhard Sessler]] and [[James Edward Maceo West|Jim West]] at [[Bell laboratories]] in 1962.<ref>{{cite journal |first1=G.M. |last1=Sessler |last2=West |first2=J.E. |title=Self-Biased Condenser Microphone with High Capacitance |journal=Journal of the Acoustical Society of America |volume=34 |date=1962 |pages=1787–1788 |doi=10.1121/1.1909130 |issue=11 |bibcode=1962ASAJ...34.1787S }}</ref> The externally applied charge used for a conventional condenser microphone is replaced by a permanent charge in an electret material. An [[electret]] is a [[ferroelectric]] material that has been permanently [[Electric charge|electrically charged]] or ''polarized''. The name comes from ''electrostatic'' and ''magnet''; a static charge is embedded in an electret by the alignment of the static charges in the material, much the way a [[permanent magnet]] is made by aligning the magnetic domains in a piece of iron.

Due to their good performance and ease of manufacture, hence low cost, the vast majority of microphones made today are electret microphones; a semiconductor manufacturer estimates annual production at over one billion units.<ref>{{cite web |last=Van Rhijn |first=Arie |url=http://www.national.com/nationaledge/dec02/article.html |title=Integrated Circuits for High Performance Electret Microphones |publisher=National Semiconductor |archive-url=https://web.archive.org/web/20100819045334/http://www.national.com/nationaledge/dec02/article.html |archive-date=August 19, 2010 }}</ref> They are used in many applications, from high-quality recording and [[Lavalier microphone|lavalier]] (lapel mic) use to built-in microphones in small sound recording devices and telephones. Prior to the proliferation of MEMS microphones, nearly all cell-phone, computer, PDA and headset microphones were electret types.{{Citation needed|date=December 2023}}

Unlike other capacitor microphones, they require no polarizing voltage, but often contain an integrated [[Microphone preamplifier|preamplifier]] that does require power. This preamplifier is frequently phantom powered in [[sound reinforcement]] and studio applications. Monophonic microphones designed for [[personal computer]]s (PCs), sometimes called multimedia microphones, use a 3.5&nbsp;mm plug as usually used for stereo connections; the ring, instead of carrying the signal for a second channel, carries power.

==== Valve microphone ====
{{Main|Valve microphone}}

A valve microphone is a condenser microphone that uses a [[vacuum tube]] (valve) [[Valve amplifier|amplifier]].<ref>{{cite web |last=Institute BV Amsterdam |first=SAE |title=Microphones |url=http://www.sae.edu/reference_material/audio/pages/Microphones.htm |publisher=Practical Creative Media Education |access-date=March 7, 2014 }}</ref> They remain popular with enthusiasts of [[tube sound]].

=== Dynamic <span class="anchor" id="Dynamic microphone"></span>===
<!-- "Dynamic microphone" and "Moving-coil microphone" redirect here. -->
[[File:Patti Smith performing in Finland, 2007.jpg|thumb|[[Patti Smith]] singing into a [[Shure SM58]] (dynamic cardioid type) microphone]]
[[File:Tauchspulenmikrofon-en.svg|thumb|left|Inner workings of a dynamic microphone]]

The '''dynamic microphone''' (also known as the '''moving-coil microphone''') works via [[electromagnetic induction]]. They are robust, relatively inexpensive and resistant to moisture. This, coupled with their potentially high [[gain before feedback]], makes them popular for on-stage use.

Dynamic microphones use the same dynamic principle as in a [[loudspeaker]], only reversed. A small movable [[induction coil]], positioned in the [[magnetic field]] of a permanent magnet, is attached to the diaphragm. When sound enters through the windscreen of the microphone, the sound wave moves the diaphragm which moves the coil in the magnetic field, producing a varying [[voltage]] across the coil through electromagnetic induction.

=== Ribbon ===
{{Main|Ribbon microphone}}
[[File:Edmund Lowe fsa 8b06653.jpg|thumb|left|upright|[[Edmund Lowe]] using a ribbon microphone]]

Ribbon microphones use a thin, usually corrugated metal ribbon suspended in a magnetic field. The ribbon is electrically connected to the microphone's output, and its vibration within the magnetic field generates the electrical signal. Ribbon microphones are similar to moving coil microphones in the sense that both produce sound by means of magnetic induction. Basic ribbon microphones detect sound in a [[#Bi-directional|bi-directional]] (also called figure-eight, as in the [[#Microphone polar patterns|diagram]] below) pattern because the ribbon is open on both sides.  Also, because the ribbon has much less mass, it responds to the air velocity rather than the [[sound pressure]]. Though the symmetrical front and rear pickup can be a nuisance in normal stereo recording, the high side rejection can be used to advantage by positioning a ribbon microphone horizontally, for example above cymbals, so that the rear lobe picks up sound only from the cymbals. The figure-eight response of a ribbon microphone is ideal for [[Blumlein pair]] stereo recording. Other directional patterns are produced by enclosing one side of the ribbon in an acoustic trap or baffle, allowing sound to reach only one side. The classic [[RCA Type 77-DX microphone]] has several externally adjustable positions of the internal baffle, allowing the selection of several response patterns ranging from figure-eight to unidirectional. 

A good low-frequency response in older ribbon microphones could be obtained only when the ribbon was suspended very loosely, which made them relatively fragile. Modern ribbon materials, including new [[nanomaterials]],<ref>{{cite journal |url=http://www.bizjournals.com/masshightech/stories/2008/02/11/story8.html |title=Local firms strum the chords of real music innovation |archive-date=2008-02-19 |archive-url=https://web.archive.org/web/20080219041634/http://www.bizjournals.com/masshightech/stories/2008/02/11/story8.html |journal=Mass High Tech: The Journal of New England Technology |date=February 8, 2008 }}</ref>{{fv |reason=Signal purity and output level, not mechanical robustness, are the claimed advantages of the new materials |date=January 2025}} have now been introduced that eliminate those concerns and even improve the effective dynamic range of ribbon microphones at low frequencies. Protective wind screens can reduce the danger of damaging a vintage ribbon, and also reduce plosive artifacts in the recording. 

In common with other classes of dynamic microphones, ribbon microphones do not require phantom power; in fact, this voltage can damage some older ribbon microphones. Some new modern ribbon microphone designs incorporate a preamplifier and, therefore, do require phantom power, and circuits of modern passive ribbon microphones (i.e. those without the aforementioned preamplifier) are specifically designed to resist damage to the ribbon and [[transformer]] by phantom power.

=== Carbon ===
{{Main|Carbon microphone}}
[[File:Western Electric double button carbon microphone.jpg|thumb|upright|[[Western Electric]] double button carbon microphone]]

The carbon microphone was the earliest type of microphone. The carbon button microphone (also known as the Berliner or Edison microphone) uses a capsule or button containing carbon granules pressed between two metal plates. A voltage is applied across the metal plates, causing a small current to flow through the carbon. One of the plates, the diaphragm, vibrates in sympathy with incident sound waves, applying a varying pressure to the carbon. The changing pressure deforms the granules, causing the contact area between each pair of adjacent granules to change, and this causes the electrical resistance of the mass of granules to change. The changes in resistance cause a [[Ohm's law|corresponding change in the current]] flowing through the microphone, producing the electrical signal. Carbon microphones were once commonly used in telephones; they have extremely low-quality sound reproduction and a very limited frequency response range but are very robust devices. The Boudet microphone, which used relatively large carbon balls, was similar to the granule carbon button microphones.<ref>{{cite web |title=Boudet's Microphone |url=http://www.machine-history.com/Boudet%20Microphone |website=Machine-History.com |archive-url=https://web.archive.org/web/20150822100052/http://www.machine-history.com/Boudet%20Microphone |archive-date=August 22, 2015 }}</ref>

Unlike other microphone types, the carbon microphone can also be used as a type of amplifier, using a small amount of sound energy to control a larger amount of electrical energy. Carbon microphones found use as early [[telephone repeater]]s, making long-distance phone calls possible in the era before vacuum tubes. Called a Brown's relay,<ref>{{cite web |title=Brown Type G Telephone Relay Owned by Edwin Howard Armstrong |url=https://americanhistory.si.edu/collections/search/object/nmah_890933 |website=National Museum of American History |access-date=June 15, 2022 }}</ref> these repeaters worked by mechanically coupling a magnetic telephone receiver to a carbon microphone: the faint signal from the receiver was transferred to the microphone, where it modulated a stronger electric current, producing a stronger electrical signal to send down the line.

=== Piezoelectric <span class="anchor" id="Piezoelectric microphone"></span>===
<!--"Piezoelectric microphone" redirects here.-->
[[File:Astatic crystal mic.jpg|thumb|Vintage [[Astatic Corporation|Astatic]] crystal microphone]]

A '''crystal microphone''' or '''piezo microphone'''<ref>{{cite journal |last1=Lee |first1=Woon Seob |last2=Lee |first2=Seung S. |title=Piezoelectric Microphone Built on Circular Diaphragm |journal=Sensors and Actuators A |volume=144 |issue=2 |date=2008 |pages=367–373 |url=http://www.pitt.edu/~qiw4/Academic/ME2080/ZnO%20circular%20microphone.pdf |archive-url=https://web.archive.org/web/20130717185137/http://www.pitt.edu/~qiw4/Academic/ME2080/ZnO%20circular%20microphone.pdf |archive-date=July 17, 2013 |doi=10.1016/j.sna.2008.02.001 |bibcode=2008SeAcA.144..367L |access-date=March 28, 2023 }}</ref> uses the phenomenon of [[piezoelectricity]]—the ability of some materials to produce a voltage when subjected to pressure{{efn|An example of this is [[potassium sodium tartrate]], which is a piezoelectric crystal that works as a transducer, both as a microphone and as a slimline loudspeaker component.}}—to convert vibrations into an electrical signal. Crystal microphones were once commonly supplied with vacuum tube (valve) equipment, such as domestic tape recorders.  Their high output impedance matched the high input impedance (typically about 10&nbsp;MΩ) of the vacuum tube input stage well. They were difficult to match to early [[transistor]] equipment and were supplanted by dynamic microphones, and later small electret condenser devices. The high impedance of the crystal microphone made it very susceptible to handling noise, both from the microphone itself and from the connecting cable.{{cn|reason=Are we sure this is about impedance?|date=April 2025}}

Piezoelectric transducers are often used as [[contact microphone]]s to amplify sound from acoustic musical instruments, to sense drum hits and trigger electronic samples, and to record sound in challenging environments, such as underwater under high pressure. [[Pick up (music technology)#Piezoelectric pickups|Saddle-mounted pickups]] on [[acoustic guitar]]s are typically piezoelectric devices that contact the strings passing over the saddle. This type of microphone is different from [[Pick up (music technology)#Magnetic pickups|magnetic coil pickups]] commonly visible on typical [[electric guitar]]s, which use magnetic induction, rather than mechanical coupling, to pick up vibration.<!--[[User:Kvng/RTH]]-->

=== Fiber-optic ===
[[File:Optimic1140 fiber optical microphone for wiki.jpg|thumb|upright|The [[Optoacoustics Ltd|Optoacoustics]] 1140 fiber-optic microphone]]

A [[Optical fiber|fiber-optic]] microphone converts acoustic waves into electrical signals by sensing changes in light intensity, instead of sensing changes in capacitance or magnetic fields as with conventional microphones.<ref>{{cite journal |last1=Paritsky |first1=Alexander |last2=Kots |first2=A. |title=Fiber optic microphone as a realization of fiber optic positioning sensors |journal=10th Meeting on Optical Engineering in Israel |editor2-first=Stanley R |editor2-last=Rotman |editor1-first=Itzhak |editor1-last=Shladov |volume= 3110 |date=1997 |pages=408–409 |url=http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=928593 |doi=10.1117/12.281371 |bibcode=1997SPIE.3110..408P |s2cid=110338054 }}</ref><ref>{{cite patent |country=US |number=6462808 |pubdate=October 8, 2002 |inventor=Alexander Paritsky and Alexander Kots |title=Small Optical Microphone/Sensor }}</ref>

During operation, light from a laser source travels through an optical fiber to illuminate the surface of a reflective diaphragm. Sound vibrations of the diaphragm modulate the intensity of light reflecting off the diaphragm in a specific direction. The modulated light is then transmitted over a second optical fiber to a photodetector, which transforms the intensity-modulated light into analog or digital audio for transmission or recording. Fiber-optic microphones possess high dynamic and frequency range, similar to the best high fidelity conventional microphones.

Fiber-optic microphones do not react to or influence any electrical, magnetic, electrostatic or radioactive fields (this is called [[Electromagnetic interference|EMI/RFI]] immunity). The fiber-optic microphone design is therefore ideal for use in areas where conventional microphones are ineffective or dangerous, such as inside [[Gas turbine#Industrial gas turbines for power generation|industrial turbines]] or in [[magnetic resonance imaging]] (MRI) equipment environments.

Fiber-optic microphones are robust, resistant to environmental changes in heat and moisture, and can be produced for any directionality or [[impedance matching]]. The distance between the microphone's light source and its photodetector may be up to several kilometers without need for any preamplifier or another electrical device, making fiber-optic microphones suitable for industrial and surveillance acoustic monitoring.

Fiber-optic microphones are used in very specific application areas such as for [[infrasound]] monitoring and [[Noise-canceling microphone|noise cancellation]]. They have proven especially useful in medical applications, such as allowing radiologists, staff and patients within the powerful and noisy magnetic field to converse normally, inside the MRI suites as well as in remote control rooms.<ref>{{cite web |last=Karlin |first=Susan |url=http://www.rt-image.com/Case_Study_Can_You_Hear_Me_Now_Technology_for_better_communication_in_the_MRI_su/content=9004J05E48B6A686407698724488A0441 |title=Case Study: Can You Hear Me Now? |website=RT-Image.com |publisher=Valley Forge Publishing |archive-url=https://web.archive.org/web/20110715212557/http://www.rt-image.com/Case_Study_Can_You_Hear_Me_Now_Technology_for_better_communication_in_the_MRI_su/content%3D9004J05E48B6A686407698724488A0441 |archive-date=July 15, 2011 }}</ref> Other uses include industrial equipment monitoring and  audio calibration and measurement, high-fidelity recording and law enforcement.<ref>{{cite web |last=Goulde |first=Berg |title=15 Best Microphones for Computer |url=https://microphonetopgear.com/microphones-for-computer/ |website=Microphone top gear |date=February 9, 2017 |access-date=March 20, 2023 }}</ref>

=== Laser ===
{{Main|Laser microphone}}

[[Laser microphone]]s are often portrayed in movies as spy gadgets because they can be used to pick up sound at a distance from the microphone equipment. A laser beam is aimed at the surface of a window or other plane surface that is affected by sound. The vibrations of this surface change the angle at which the beam is reflected, and the motion of the laser spot from the returning beam is detected and converted to an audio signal.

In a more robust and expensive implementation, the returned light is split and fed to an [[interferometer]], which detects movement of the surface by changes in the [[optical path length]] of the reflected beam. The former implementation is a tabletop experiment; the latter requires an extremely stable laser and precise optics.

A new type of laser microphone is a device that uses a laser beam and smoke or vapor to detect sound [[vibration]]s in free air. On August 25, 2009, U.S. patent 7,580,533 issued for a Particulate Flow Detection Microphone based on a laser-photocell pair with a moving stream of smoke or vapor in the laser beam's path. Sound pressure waves cause disturbances in the smoke that in turn cause variations in the amount of laser light reaching the photodetector. A prototype of the device was demonstrated at the 127th Audio Engineering Society convention in New York City from 9 through October 12, 2009.

=== Liquid ===
{{Main|Water microphone}}

Early microphones did not produce intelligible speech, until Alexander Graham Bell made improvements including a variable-resistance microphone/transmitter.  Bell's liquid transmitter consisted of a metal cup filled with water with a small amount of [[sulfuric acid]] added. A sound wave caused the diaphragm to move, forcing a needle to move up and down in the water. The electrical resistance between the wire and the cup was then inversely proportional to the size of the water meniscus around the submerged needle.  Elisha Gray filed a [[Patent caveat|caveat]] for a version using a brass rod instead of the needle.{{when|date=February 2019}}  Other minor variations and improvements were made to the liquid microphone by Majoranna, Chambers, Vanni, Sykes, and Elisha Gray, and one version was patented by [[Reginald Fessenden]] in 1903. These were the first working microphones, but they were not practical for commercial application.  The famous first phone conversation between Bell and Watson took place using a liquid microphone.

=== MEMS ===
{{Main|Microelectromechanical systems}}
[[File:Asus Zenbook UX32V - webcam module - AK230 0539L 4911C-0108.jpg|thumb|MEMS microphone Akustica AKU230]]

The [[Microelectromechanical systems|MEMS]] (microelectromechanical systems) microphone is also called a microphone chip or silicon microphone. A pressure-sensitive diaphragm is etched directly into a silicon wafer by MEMS processing techniques and is usually accompanied with an integrated preamplifier.<ref>{{Cite web |last=Rose |first=Bruce |title=Comparing MEMS and Electret Condenser (ECM) Microphones |url=https://www.cuidevices.com/blog/comparing-mems-and-electret-condenser-microphones |website=CUIDevices.com |date=January 8, 2019 |access-date=March 27, 2023 }}</ref> Most MEMS microphones are variants of the condenser microphone design. Digital MEMS microphones have built-in [[analog-to-digital converter]] (ADC) circuits on the same CMOS chip making the chip a digital microphone and so more readily integrated with modern digital products. Major manufacturers producing MEMS silicon microphones are Wolfson Microelectronics (WM7xxx) now Cirrus Logic,<ref>{{cite web |url=http://www.marketwatch.com/story/cirrus-logic-completes-acquisition-of-wolfson-microelectronics-2014-08-21|title=Cirrus Logic Completes Acquisition of Wolfson Microelectronics |website=MarketWatch.com |access-date=August 21, 2014 }}</ref> InvenSense (product line sold by Analog Devices<ref>{{cite press release |url=http://www.analog.com/en/about-adi/news-room/press-releases/2013/10_14_13_adi_to_sell_microphone_product_line_to_in.html |title=Analog Devices to Sell Microphone Product Line to InvenSense |publisher=Analog Devices |access-date=November 27, 2015 }}</ref>), Akustica (AKU200x), Infineon (SMM310 product), Knowles Electronics, Memstech (MSMx), NXP Semiconductors (division bought by Knowles<ref>{{cite web |url=http://investor.knowles.com/phoenix.zhtml?c=252194&p=irol-newsArticle&ID=1884042|title=Knowles Completes Acquisition of NXP's Sound Solutions Business |publisher=Knowles |access-date=July 5, 2011 }}</ref>), Sonion MEMS, Vesper, AAC Acoustic Technologies,<ref>{{cite web |url=http://seekingalpha.com/article/157790-mems-microphone-will-be-hurt-by-downturn-in-smartphone-market |title=MEMS Microphone Will Be Hurt by Downturn in Smartphone Market |website=[[Seeking Alpha]] |date=August 23, 2009 |access-date=August 23, 2009 }}</ref> and Omron.<ref>{{cite web |url=http://www.omron.com/media/press/2009/11/c1125.html |title=OMRON to Launch Mass-Production and Supply of MEMS Acoustic Sensor Chip |access-date=November 24, 2009 }}</ref>

More recently, since the 2010s, there has been increased interest and research into making piezoelectric MEMS microphones which are a significant architectural and material change from existing condenser style MEMS designs.<ref>{{cite web|url=http://www.eetimes.com/document.asp?doc_id=1324827|title=MEMS Mics Taking Over|work=EETimes}}</ref>

=== Plasma ===
In a plasma microphone, a plasma arc of ionized gas is used. The sound waves cause variations in the pressure around the plasma in turn causing variations in temperature which alter the conductance of the plasma. These variations in conductance can be picked up as variations superimposed on the electrical supply to the plasma.<ref>{{cite journal |first1 = Hiroshi |last1 = Akino |first2 = Hirofumi |last2 = Shimokawa |first3 = Tadashi |last3 = Kikutani |first4 = Jackie |last4 = Green |date= April 2014 |pages = 254–264 |title = On the Study of the Ionic Microphone |volume = 62 |journal = [[Journal of the Audio Engineering Society]] |issue = 4 |doi = 10.17743/jaes.2014.0013}}</ref> This is an experimental form of microphone.

=== Speakers as microphones ===
A loudspeaker, a transducer that turns an electrical signal into sound waves, is the functional opposite of a microphone. Since a conventional speaker is similar in construction to a dynamic microphone (with a diaphragm, coil and magnet), speakers can actually work "in reverse" as microphones. [[Reciprocity (engineering)|Reciprocity]] applies, so the resulting microphone has the same impairments as a single-driver loudspeaker: limited low- and high-end frequency response, poorly controlled [[directivity]], and low [[Sensitivity (electronics)|sensitivity]]. In practical use, speakers are sometimes used as microphones in applications where high bandwidth and sensitivity are not needed such as [[intercom]]s, [[walkie-talkie]]s or [[Voice chat#Voice chat in gaming|video game voice chat]] peripherals, or when conventional microphones are in short supply.

However, there is at least one practical application that exploits those weaknesses: the use of a medium-size [[woofer]] placed closely in front of a "kick drum" ([[bass drum]]) in a [[drum set]] to act as a microphone.  A commercial product example is the Yamaha Subkick, a {{convert|6.5|in|adj=on}} woofer shock-mounted into a 10" drum shell used in front of kick drums. Since a relatively massive membrane is unable to transduce high frequencies while being capable of tolerating strong low-frequency transients, the speaker is often ideal for picking up the kick drum while reducing bleed from the nearby cymbals and snare drums.<ref>{{cite web |url=http://recordinghacks.com/reviews/tapeop/yamaha-subkick/ |title=Yamaha SubKick – The Tape Op Review |first=Larry |last=Crane |website=RecordingHacks.com |date=July 2004 |access-date=April 11, 2023 }}</ref>