I see a thread by you about that about a speaker where the woofer covers 400hz and below. Isn’t something like the Kef Reference 1 or TAD ME-1 the closest to that concept in practice--basically a 3-way coaxial?
I'm not sure what thread you are talking about, I've posted many, and I'm not the biggest proponent of WAWB speakers, but given your post, I though you might find it an interesting idea.
WAWB is a true 2-way, not a 3-way with coaxial.
The idea is to use a relatively small (3"-4") wide band driver to cover the mid-hundreds all the way up through the top octave. Takes crossovers completely out of the vocal range. You should visit DIYaudio or another site for more information on current thinking of this type of design.
Another way to think of a WAWB is a close cousin of full-range, single driver speakers, similar to the Fostex or Markaudio type of drivers.
https://www.madisoundspeakerstore.com/full-range-speaker-kits/
Let me know if you try any of them,
Erik