These days it is not unreasonable to get low enough lows for bass guitar from a 5" speaker, especially a pair or more of them. Instrument speakers (the drive units themselves I mean) never bothered to miniaturize like their hifi brethren did. You can use hifi speakers, but they are usually too compliant (detail vs robustness - expecting compressed program material vs raw instrument signal with all it's dynamic range) and do not have the upper midrange resonant peak that (mostly guitar playing) musicians (have grown to) love. There is some crossover precident already, but mostly with PA vs HiFi gear (and PA still goes big, except in the case of line arrays).
A bud an I are developing some cabs. First one will be a 1x12. I wanted to do a 2x10 or smaller as well (was looking at like 4x4) but decided to lead with something a bit more usual.
Also don't be fooled into thinking it is a 'ported' (bass reflex) cab just because there is a port. It very well maybe, but there are other possibilities.
Also if the response is 40Hz and up it will not do a low B fundamental (but will be fine with the 2nd harmonic and up, so unless youre playing an EB0 it should be fine or at least acceptable).
