thanks to all contributors.
I didnt place data because right now the discussion is philosophical.
My skills in project sub from the scratch are close to zero, so this is the first challenge, and having such kind of confrontation with more skilled builders to me is the basic to build my trusting!
the goal is design a 3 way system, that in my mind is:
-a sub part
-a mid 5"x2
-a tweeter
keep in mind that this project is far from be the best multiway speaker that u have heard, but more a thing builded to have in litlle the fashion or the jamaican soundsystem: so it will be mono, and all in one coloumn (the two things are strictly related, i imagine that there is no sense to make stereo for just one source).
So the hard part is making the thing little as much is possible and still have some bass. hard!
the little sub needs to have some jamaican flavour, so it will looks as a scoop, but having a backloaded horn for driver that are smaller than 15" imo have no sense.
So the compromise size is 6.5" , in a fake scoop that will be a reflex.
keeping in mind that 6,5*2= 13" thats make me thinking that in same space i can fit a single 10" maybe layed down as bandpass, with some fake speaker in front that simulate the scoop fashion. So that is the nature of the question.