References - Patents
Yes it's a shoe
 The following table lists all of the patents found so far relating to the production of sound using massless means.  There are many more around related fields, this list is limited to those specifically related to sound reproduction/recording. There is a brief note attempting to summarise the type of speaker the patent describes, and also a class description which categorises the particular invention. If you wish to find the full detail of a particular patent it is recommended to look at the espacenet website and search for the patent number in the form US2793324 for example. As you can see, there have been a good many patented designs for over 120 years - proving that massless speakers are nothing new! Sort the table by clicking the column headings, some titles are shortened.
Country Patent No. Title Author Date Class Notes
US 164458 Improvement in pyrophones Frederic Kastner 1873 - Hydrogen flame in tubes pipe organ
US 201760 Speaking Machine Edison 1878 - Compressed air, nearly massless for ref
GB 21629 Singing arc Duddell 1900 A Convert DC to audible AC using arc
GB 190215527 Improvements in or relating to wireless... Blondel 1903 A Speaker, mic and circuits based on Duddell
GB 15599 ? Poulsen 1903 - Radio transmitter based on Duddell
GB 190604585 Improvements in and relating to Hermanus 1906 A Arc microphone, piston against electrode
GB 190628125 Improvements in wireless telephony Forest 1907 A Uses Duddell and Simon's speaking arc
GB 191407202 Improved method of trans Stille 1915 A Arc microphone (reverse of singing arc)
GB 264811 Improvements relating to elec General Electric 1927 B Point to plane corona discharge
GB 265958 Improvements relating to elec General Electric 1928 C Points on a disc corona wind.
US 1680694 Sound reproducing method and apparatus Ramsey 1928 B Horn loaded plasma speaker mod RF
US 1685075 Intertransposition of sound Lindenblad, RCA 1928 C Point to air/ground corona discharge. 189 patents!, Swedish
US 1723244 Method of and apparatus for reproducing sound Lilienfeld 1929 C Modulate air flow around disc
US 1702951 Sound-emitting apparatus Ruben 1929 B Horn loaded plasma
GB 303175 Loudspeaker arrangement Loewe 1930 C Grid modulated ion source
US 1758993 Sound reproducer Wolff 1930 C Many points corona discharge. Ref to above patent 1695075 wrong!
US 1751888 Sound-emitting device Ruben 1930 C Heated cathode ion speaker
US 1806745 Sound Producing Device De Forest 1931 B Modulate gas flow with high voltage
US 2768246 Electrical Transducer Klein S. 1956 B Ionovac, Also-GB756546, CH317527, DE1095883, FR1041790, US2768246
GB 757358 Improvements in or relating to Klein S. 1956 B Ionovac, Also-US2847516, GB757111, FR1041790, BE519086, FR67664E
US 2793324 Ionic triode speaker Halus, Holcomb 1957 B Corona discharge around a hole
GB 792312 Improvements in and relating to Klein S. 1958 B Multi horn Ionovac
US 2949550 Electrokinetic apparatus Townsend Brown 1960 C Corona wind
US 3105124 Inertialess Transducer Torn 1963 B Dukane ionovac
US 3185778 Apparatus for producing sound Gianni, Ducati 1965 B Horn loaded plasma
FR 1427695 Appareil sonore electrohydro Electrokinetics 1966 C Corona wind wire with backplate shapes
US 3018394 Generation and transmission Townsend Brown 1967 C Corona wind
US 3476887 Ionic electroacoustic transducer Seligson, Lanier 1969 C Many points to blades corona wind (blades all vertical, points only one side)
GB 1199859 Method etc. generating an acoustic output United Aircraft Corp 1970 B Modulating flame with high voltage, US3565209
GB 1274875 A system for imparting movem Townsend Brown 1972 C Corona triode with vertical bars+wires.
DE 2115544 Koronaphon Walter 1972 B Circuit for a plasma loudspeaker (modulated supply?)
FR 2246151 none Doucet, Henri 1975 C Corona wind
JP 5167735 Diaphragm on ionic speaker 1976 B Plasma speaker with diaphragm(!) to stop gas
JP 53141612 Grid controlled ionic wind loud Kiyoshi 1978 B Corona triode, wires, single ended and push pull.
JP 53142218 Ionic Wind Loudspeaker Kiyoshi 1978 B Corona triode, just single ended, points
JP 53137128 Ionic Wind Loudspeaker Kiyoshi 1978 B Corona triode, points, single ended and push pull.
GB 2023373 Plasma Loudspeaker Hill 1979 B Plasmatronic, glow discharges in parallel. US4219705, JP54143225, JP2918300, FR2422314, DE2913804
JP 54119914 Ion Speaker Hatake Kiyoshi 1979 B Replaceable plasma speaker tube
EP 17885 Corona-effect loudspeaker Klein S. 1980 B Magnat
EP 17886 Corona-loudspeaker Klein S. 1980 B Magnat
US 4306120 Sound emitter Klein S. 1981 B Magnat/Ionovac
EP 65911 Ionic electro-acoustic transducer Bondar 1982 C Plasmasonic, Also-US4460809, JP58001395, FR2506551, EP0065911
US 4460809 Process and device for converting a periodic... Bondar 1984 C Ionic pins and plates
US 4464544 Corona-effect sound emitter Klein S. 1984 B Magnat
FR 2544951 Corona effect loudspeaker Klein S. 1984 B Magnat
US 4482788 Transducer for the transformation Klein S. 1984 B Also EP0017886, SU1175352, JP55140400, FR245444, ES8100754
FR 2588710 Ionic electroacoustic transducer Deraedt 1987 C Push-pull corona wind
WO 8807785 Electrokinetic transducing met Lee 1988 C Corona wind, Offset wires to thicker bars.
US 4789801 Electrokinetic transducing met Lee 1988 C Corona wind, Offset wires to thicker aerodynamic bars.
EP 370846 Electroacoustic Transducer Fourriere 1990 C Tolteque, Corona/Glow modulated by plates. JP2174398, FR2638930
FR 2685156 Tranducteur electroacoustique, et enceinte... Bayle Pierre, Gibert Alain 1991 C Many point to plane corona?
JP 4027300 Method and device for arc sound Eizo 1992 A Arc/flame nozzle, a TIG welder
US 5220246 Method and apparatus for tran Ide, Hashimoto 1993 A Possible glow discharge (arc column), single point to plane. Based on DC TIG welder.
JP 6327099 Speaker utilizing DC corona dis Masaaki 1994 B Point to plane corona discharge,+ push pull
GB 2312590 Corona Discharge Loudspeaker Howard 1997 C Corona wind wires with grids either side.
GB 2403372 Corona Discharge Loudspeaker Chambers 2004 C Corona wind
WO 127810 Electroststic Loudspeaker and ... Krichtapovitch 2007 C Kronos EPA application (not granted yet, company closed), corona wind
JP 2010141858 Sound generator Sony Corp 2008 B Sony's attempt at a plasma tweeter design
CN 101778327 Electricity and sound conversion... Yao Zongdong 2010 B Plasma speaker controlled by magnetic field, or not the translation is vague
CN 202218397 Plasma loudspeaker Zhao Ge, Gao Yifeng, Cao Dong 2011 B Plasma speaker, classic style with two electrodes, a reflector behind
DE 102010026112 Plasma tweeter e.g. teslums tweeter, for e.g. acoustic lab Braun Alexander 2012 B Plasma speaker on tesla coil
RU 2496254 Electric-arc loudspeaker Boris G. Viger 2012 B Plasma tweeter of Viger Audio
CN 101820573 Control device for plasma loudspeaker and plasma loudspeaker Lu Yulong 2013 B Plasma speaker amp
JP 5281428 Microphone Yu Akino 2013 B Plasma based microphone
JP 5474614 Electroacoustic transducer Yu Akino 2014 B Plasma speaker
JP 5777540 Electroacoustic transducer Yu Akino 2015 B Plasma speaker and microphone
CN 205902064 Electron tube ionic loudspeaker Zhang Zaifei 2017 B Basic plasma speaker valve amplifier
JP 6099143 Electroacoustic transducer Yu Akino 2017 B Plasma speaker
CN 107948895 Microwave plasma loudspeaker Fu Wenjie 2018 B Microwave generated plasma
CN 110430515 Improved plasma loudspeaker Hu Zhenqiang 2019 B Circular arrangement of plasmas
WO 2019135196 Electronic effects device and method Ilja KRUMINS, Martins MELKIS, Kristaps KALVA 2019 B Plasma in a gas discharge tube
EP 3513576 Plasma speaker Gilligan 2020 B Multiple small plasma tweeters to create a full-range plasma
US 201862627839 System and Method for Acoustic to Electronic Transduction Johan Carlsson 2020 B Plasma microphone for structural listening
Classes of transducer :
A Arc discharge
B Glow discharge / Plasma
C Corona wind (ion cloud)

Some of my thoughts about Patenting.


Info about plasma tweeters

and ionic loudspeakers

with high voltage ion cloud

and corona wind speakers
and more plasma and ion info.

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