Plasma speakers anyone with info?

Those green tanks for the Plasmatronics were filled with HELIUM, not argon, as I recall (and you and I heard the same ones at the same time, Bear!)

The ozone emitting speakers you guys are talking about was called Dayton-Wright. They were big, heavy, and sounded great. I understand that the membranes failed pretty readily, so they went out of business. The original speaker that Joe Grado used as reference was AR1Ws for the low end, Janzen electrostats for the mids, and the Ionivac supertweeter for the highs.

The Dayton-Wrights were electrostats, not plasma speakers. The diaphragms were enclosed in "bags" containing (as I recall) sodium hexafluoride gas, so I doubt they emitted any ozone (which results from breaking down AIR or other gas containing oxygen, not sodium hexafluoride)

I've heard, though only briefly, the Acapella. The tweeter is very nimble and nice sounding. The Hill I heard MANY years ago (around 1979). The Hill required a bottle on inert gas that is injected into the ion tweeter to prevent corrosion of the electrode that ionized the gas. You would get a wiff of ozone being discharged by the speaker.

A few years ago, the DIY magazine AudioXpress (at least I think it was this magazine) had an article on how to make your own plasma tweeter. Their design did not require injection of a gas around the electrode. The electrode had a quite limited life, but, it was cheap and fairly easy to build spares.

Dayton Wrights had "cells" enclosing the membranes and containing sulfur hexafluoride (SF6) gas. There is no mention of ozone being produced in the documentation, since the gas filled enclosures were not intended to leak (a Schrader valve on the bottom of each speaker, similar to one found on a car or bicycle, was present for adding SF6 if ever needed). The most frequent cause of failure (leaks) were cats, mentioned in the manual. Cats like to jump to high places, and the punctures of the enclosures were a certain distance off the floor where the cat(s) dug their claws in. The XG10s I have work perfectly, never a leak in their history, I was told by the previous, original owner.

Back on topic, the Acapella tweeter produces ozone which is dissipated in the throat of the horn before it escapes to the room. I don't know about other manufacturers, but ozone production is a very significant problem to be dealt with (ask Nelson Pass or Alan Hill).