While maybe not a major breakthrough Thiels 3.7 midrange is very innovative and well designed. It is my personal reference point for purity of midrange and vocal reproduction.
As an R&D/Process Engineer (Mechanical by degree) I see a lot of ideas and designs, and lots of them flop. Jim Thiel not only had great concepts but fallow through to make them really work in the real world. Now that is true genius.
3.7 midrange paper