Editing Loudspeaker (section)

===Without a diaphragm===

====Plasma arc speakers====
{{Main|Plasma speaker}}
[[File:Moeller Plasma.jpg|thumb|upright|Plasma speaker]]

[[Plasma arc loudspeaker]]s use electrical [[Plasma (physics)|plasma]] as a radiating element. Since plasma has minimal mass, but is charged and therefore can be manipulated by an [[electric field]], the result is a very linear output at frequencies far higher than the audible range. Problems of maintenance and reliability for this approach tend to make it unsuitable for mass market use. In 1978 Alan E. Hill of the Air Force Weapons Laboratory in Albuquerque, NM, designed the [[Plasmatronics]] Hill Type I, a tweeter whose plasma was generated from [[helium]] gas.<ref name="nutshellhifi">[http://www.nutshellhifi.com/library/speaker-design1.html Hill Plasmatronics] described. Retrieved March 26, 2007.</ref> This avoided the [[ozone]] and [[NOx]]<ref>{{cite web| url=https://massless.info/images/NOxinplasmareactors.pdf| title=NOx production in plasma reactors by pulsed spark discharges, J.Phys, 2020}}</ref> produced by [[Radio frequency|RF]] decomposition of air in an earlier generation of plasma tweeters made by the pioneering DuKane Corporation, who produced the Ionovac (marketed as the Ionofane in the UK) during the 1950s.<ref>{{cite web|url=https://www.radiomuseum.org/r/dukanecorp_ionovac_plasma_tweeter_14a435a.html |title=Ionovac Plasma Tweeter |website=RadioMuseum.org |access-date=October 12, 2021 }}</ref>

A less expensive variation on this theme is the use of a flame for the driver, as flames contain ionized (electrically charged) gases.<ref>{{cite magazine |url=https://deramp.com/swtpc.com/PopularElectronics/May1968/Flame_Amplification.htm |title=Flame Amplification and a Better Hi-Fi Loudspeaker? |via=DerAmp.com |magazine=Popular Electronics |publication-date=May 1968 |access-date=October 12, 2021 }}</ref>

====Thermoacoustic speakers====
In 2008, researchers of Tsinghua University demonstrated a [[thermophone|thermoacoustic loudspeaker]] (or ''thermophone'') of [[carbon nanotube]] thin film,<ref>{{cite journal |last1=Xiao |first1=Lin |author2=Kaili Jiang |title=Flexible, Stretchable, Transparent Carbon Nanotube Thin Film Loudspeakers |journal=Nano Letters |date=2008 |volume=8 |issue=12 |pages=4539–4545 |doi=10.1021/nl802750z |pmid=19367976 |bibcode=2008NanoL...8.4539X }}</ref>  whose working mechanism is a thermoacoustic effect. Sound frequency electric currents are used to periodically heat the CNT and thus result in sound generation in the surrounding air. The CNT thin film loudspeaker is transparent, stretchable and flexible.
In 2013, researchers of Tsinghua University further present a thermoacoustic earphone of carbon nanotube thin yarn and a thermoacoustic surface-mounted device.<ref>{{cite journal |last1=Wei |first1=Yang |author2=Xiaoyang Lin |title=Thermoacoustic Chips with Carbon Nanotube Thin Yarn Arrays |journal=Nano Letters |date=2013 |doi=10.1021/nl402408j |pmid=24041369 |volume=13 |issue=10 |pages=4795–801 |bibcode=2013NanoL..13.4795W }}</ref> They are both fully integrated devices and compatible with Si-based semiconducting technology.

====Rotary woofers====
A [[rotary woofer]] is essentially a fan with blades that constantly change their pitch, allowing them to easily push the air back and forth.  Rotary woofers are able to efficiently reproduce [[Infrasound|subsonic]] frequencies, which are difficult to impossible to achieve on a traditional speaker with a diaphragm.  They are often employed in movie theaters to recreate rumbling bass effects, such as explosions.<ref>{{cite web |url=http://www.iar-80.com/page142.html |title=Eminent Technology TRW-17 Subwoofer Part I: The Only Subwoofer |website=International Audio/Video Review |access-date=April 29, 2024 }}</ref><ref>{{cite web |last=Guttenberg |first=Steve |date=August 29, 2010 |title=World's Most Amazing Subwoofer Has No Woofer |url=http://www.cnet.com/news/worlds-most-amazing-subwoofer-has-no-woofer/ |website=CNET |access-date=April 29, 2024 }}</ref>