In the early 1950's, Arthur A. Janszen, my father, pioneered the first practical electrostatic speaker. In the process, he happened to be introducing the first high fidelity tweeter to the world. It might seem incredible, but with only one exception, after all these years, electrostatic tweeters are still the highest in fidelity, and likely to remain so.
What's the exception? It's called a plasma tweeter. This is an electric flame, like contained lightning, that grows and shrinks in response to an audio signal. It works nicely, but has a number of safety and practicality issues.
Can’t think of any off hand…
John
John Mayberry
VP, Engineering
Emmaco, Inc.