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History

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There is an excellent site on the history of air speakers and info about my projects at www.airspeaker.co.uk .

Here are a few words that may get some hits on the subject around my work.  It is more to do with the history around high voltage discharge loudspeakers than the history of Audio Chambers, best to look at the news log for that.

Firstly, most work to date has been done around the plasma tweeter.  Plasma tweeters can be classified as a high voltage corona discharge that is typically generated with RF and then modulated, much like a radio transmitter.  They are tweeters because the plasma is not capable of generating lower frequency sounds.

These plasma tweeters are also known as ion tweeters or ionic tweeters.  This is because the plasma is created by a stream of ions flying off the end of the high voltage tip.  Most work and patents around these devices appear to have been done by Siegfried Klein.  He has been instrumental in the development of the Dukane Ionovac, also known later as the Fane Acoustics Ionofane and the Electro-voice T-3500 and referred to as the Ionophone.  Then he appears to have gone on to develop the Magnat MP-1.  None of these are now made and a large number of hobbyists have had a go at making similar devices.

More accurately those devices would be referred to as cold plasma corona discharge loudspeakers.  The corona discharge is a high voltage, low current discharge generating the cold plasma. Plasma is the fourth state of matter and is basically a highly energised gas.  Plasmas can be created in many ways but these loudspeakers generally use high voltage discharge.  These plasmas are "cold" ones because, although they may be several thousand degrees centigrade, thermal equilibrium between ions and electrons is not reached.  A hot plasma is usually generated in suns and nuclear explosions, or in a tokomak and the thermal equilibrium can allow the plasma to maintain itself.

Another type of corona discharge loudspeaker is the corona wind or ion cloud loudspeaker. Known developers of these are Dr. D.M. Tombs (afterwards Gerald Shirley) and Nelson Pass.  These devices are still a corona discharge but at a lower drive level per point than the single point tweeters and then spread over many points or wires.  These speakers can produce the whole frequency spectrum.  The only commercial example of this type of loudspeaker was the Audio Reference Plasmasonic headphone, associated with Henry Bondar and Jean-Claude Fourriere.  Building a large version of this type of loudspeaker proves difficult and dangerous.  High voltage is present over a large area, generating large amounts of ozone (toxic in high quantities).  Also the background noise level is generally too high and sound levels difficult to get high.

There have been other attempts at corona devices.  These include; Corona Acoustic various types, CSE Inc. A-3000, Phonogen Model-1A and the Real Onkyo Realon range.  The only current commercial corona device I have come across is the Acapella Ion TW-1.  They use this in their high end (very high!) loudspeakers and also sell it on its own for over 8000 euros.

Besides all of these corona technology based devices there is another form of plasma from glow discharges that has been exploited.  This was used in the Hill Plasmatronic Type 1, Model 1-100-A.  The glow discharge is still a high voltage discharge but with more current than a corona producing a more stable glowing plasma.  Hill used inert helium gas pumped into the plasma chamber in an effort to reduce oxidation.  This device was also a tweeter, supplemented by a cone mid/bass unit.  I'm not sure if the AHL Tolteque demonstrated in 1992 was also glow discharge or corona discharge but Tolteques sold after were electrostatic.

This summarises some results of research I have done, mostly in an attempt to get some hits on the website so don't flame me too much if something is wrong (though I would like to know!).  The loudspeaker I am working on has elements of these technologies behind it and then goes on to the next step to produce a full-range high voltage discharge loudspeaker.  Cannot say any more for now.

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