Plasma speakers anyone with info?

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).

Where I work.....a large Semiconductor Manufacturer, we use SF6 in plasma etchers...to etch Silicon. I wouldn't want a cylinder in MY house! Not to mention the EPA showing up to monitor emissions from my Stereo, of all things.
My cats NEVER went near my Maggies....which is supposed to be a problem.
Fluorine compounds in the house? No way!

Magfan, to each his own...ESLs are strongly preferred here over other planar technologies, especially for low level detail. SF6 is more difficult to get these days but not impossible. It does have some benefits. Bias voltage can be much higher than with air (the XG10s with XIM-11 pro unit run around 15-16 kV), and the speed of sound through it is about 1/3 that through air. Wright used that characteristic in the matching XW10 subwoofers (and Watson Labs woofer modules) which have two special 10" woofers and (you guessed it) bags filled with SF6 inside the sealed enclosures. Flat to 20 Hz.