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 ions in the brand name of his first tweeter, the Ionophone is a plasma tweeter as was the later Magnat MP range of tweeters. This made the term ionophone a popular one to describe plasma loudspeakers, although previously it was used for radio receivers and telephone speakers (Wireless World 1922 and Richard Engler patent 1923).