You need at least 3 ways to have sufficient displacement for bass reproduction without compromising speaker directivity at higher frequencies.
Drivers like Mangers and full-range units with whizzer cones count as 2-ways, where the cross-over between the two is mechanical instead of electrical.
A horn couples the air in the throat to the air at the mouth so linear displacement is the same at both ends; in effect providing MUCH more surface area. A full-range whizzer-coned driver in a back-loaded horn is a 3-way.
A 2-way stand-mounted monitor plus a sub-woofer is a 3-way with independant placement for the bass-unit.
This is orthagonal to what the best compromises are once you limit price - more lower quality drivers, reduced output limits, missing the last two octaves (your brain does a reasonable job filling in the fundamental from harmonics)...
Drivers like Mangers and full-range units with whizzer cones count as 2-ways, where the cross-over between the two is mechanical instead of electrical.
A horn couples the air in the throat to the air at the mouth so linear displacement is the same at both ends; in effect providing MUCH more surface area. A full-range whizzer-coned driver in a back-loaded horn is a 3-way.
A 2-way stand-mounted monitor plus a sub-woofer is a 3-way with independant placement for the bass-unit.
This is orthagonal to what the best compromises are once you limit price - more lower quality drivers, reduced output limits, missing the last two octaves (your brain does a reasonable job filling in the fundamental from harmonics)...