Magnat MP-02 Plasma tweeters cannot be matched, not even by esl’s, the plasma gas is the diaphragm so there’s no mass, their FR is out to 1/2megahertz.!!! Ones with horns aren't quite as good, but still better than anything else.
https://www.ebay.com.au/itm/Magnat-Plasma-MP-02-ion-tweeter-massless-air-plasma-speaker-Plasmahochto...
Cheers George