There's a lot more material online about Dr. Siegfried Klein, rightly so, as he has contributed the most to the field of massless loudspeakers with two distinctly different commercial designs created over 4 decades. He was a prolific inventor and developer of massless tweeters from the '50s through to the '80s. Using the ions in the brand name of his first tweeter, the Ionophone is actually a plasma tweeter as was the later Magnat MP range of tweeters.