I have a pair of duKane Ionovacs in the basement. I am afraid of them and I don't like ozone. If anyone wants to buy them I'll sell them.
They are reciprocating flare horns (I think)
the trouble with all these ionization tweeters is that they are like having a tesla coil in your stereo . Tesla coils are a bad idea around non tube electronics.
EV also sold the duKane Ionovac as the EV T3500. The big problem with these (besides the ozone, of course) was (is) very low sensitivity, even with horn loading. I believe (??) that the horn on the Ionovacs (duKane or EV-branded) is a diffraction horn not unlike that used on the EV T35 family.
EV, bless their hearts, still has the docs for the T3500 on their website
That part of the EV website is down as I type this
but here's an archive copy, if anyone's interested.
I will also mention in the context of plasma drivers/tweeters.
1) The Hill Plasmatronics Type 1 was an (almost) full range plasma loudspeaker -- Hill used helium rather than air to generate the plasma, thus eliminating (or minimizing) the ozone issue.
2) Nelson Pass, famously, injured himself
via ozone exposure/inhalation working on an extended range plasma loudspeaker.