Plasma Tweeters - Do they still exist?

I remember reading decades ago about tweeters that use a plasma flame to emit high frequency audio. The obvious benefit: extremely low mass. 

I do not recall how the plasma flame was generate and how exactly the flame was agitated with the sound signal (I assume plasma is magnetic and magnets are used). 

I remember the obvious disadvantage was the high production of O3 (3 oxygen atoms) and its caciogenic tendency in high concentrations. 

Just wondering if any are still around (you know, could leave the windows open when listening :-).