The most dynamic speaker you've heard...

Dynamic & loud are not equal. The K-horns are probably close to both. It doesn't have to be a horn to be dynamic. It is easier for a horn to be loud.

Do you mean like Motzart's "Surprise" symphony, or Mahler's 6th (last of final movement?)

Seems like there is a little bit of clarity needed when discussing this topic. I have seen only in one place the specs of sensitivity and efficiency. If you can unerstand one speaker, a raw driver had an efficieny of 6%, and a sensetivity of 97db (?). Some horns are as much as 25% efficient, which is way more than just the driver. Not a lot of this stuff is actually published from what I see.

I driver whith a sensitivty nearing 100db in a horn should be able to deliver the most impressive dynamics an most any loudness level. Unless the program material has been compressed, that is.

Feild coil driver uses an electromagnet instead of a "permanent" magnet like a ceramic magnet because they're easy make or an Alnico V, or now rare earth magnets (neodymium.) Usually very costly, but I think that they're
overpriced.