Two ways to make a three way

[Mosquito]

Can anyone give examples of OP's options 1 & 2? Option 1 is to use filler mid, and option 2 is to use wideband mid. I wonder what successful designs actually used these approaches.

Well one for all is the famous Snell that was dissected by Troels Gravesen, the other can be some vintage Bang & Olufsen units, I believe..

 

[Juhazi]

Some things to keep in mind
- a 4" mid with shallow xo gets stressed with high spl easily , use xo around 400Hz and upper 3-4000Hz
- smooth directivity is ideal, a smallish mid is easier than 5-6"
- what is box type and size? Floor or stand, how wide?
- do you want good low bass to 30Hz or do you use subwoofers anyway. One or two bass units, closed, reflex or TL?
- these are rather difficult to design as passive and easily get expensive, perhaps first follow a good project and modify it
- consider also using minidsp and multiple amplifiers

I like these diy projects but I haven't heard any of them... (not in order)
Poor Man' (my favourite)
Zaph|Audio - ZDT3.5
SBAcoustics-3WC
MiniStatements
KS-263

 

[Mosquito]

I think I will try a trick like this one, plus a rear mounted filler, and flush mounted tweeter, to keep centers distance as little as fisically possible

 

[Mosquito]

Some things to keep in mind
- a 4" mid with shallow xo gets stressed with high spl easily , use xo around 400Hz and upper 3-4000Hz
- smooth directivity is ideal, a smallish mid is easier than 5-6"

I like these diy projects but I haven't heard any of them... (not in order)
Poor Man' (my favourite)
Zaph|Audio - ZDT3.5
SBAcoustics-3WC
MiniStatements
KS-263

Agree on all that,
KS-263 and the GA Tech three way Laboratory speaker (Marshal Leach site) are the kind that I like the most