I noticed no one has mentioned the Heil Air Motion transformer; that came out in the 70's I believe, and there were some two way speakers that utilized it. Although I liked the highs that two way produced, the mid-range just wasn't mellow enough.
I liked the highs so much that I designed 3 way speakers with that for the tweeter, 12 inch woofer, and 6 inch midrange. I engaged a crossover engineer to design the crossover (far too complicated for me), and that completed my speaker; it's completely neutral, and takes on the quality of whatever electronics are used; you can tell a change in interconnects immediately.
Although I'm listening to them now, I would never do it again; I spent 20 years redoing the cabinets until I was satisfied, but that's the only way to get precisely what you want.
I noticed a lot of speakers lately are using miniature Heil Tweeters.
https://en.wikipedia.org/wiki/Air_Motion_Transformer
http://www.simplyspeakers.com/ess-replacement-tweeter-air-motion-transformer-amt-heil.html
Enjoy the music.