whats the smallest ported box i can do for...

An Alpine 12" Type-R

The specs say 0.75- 1.75 cu ft, but 0.75 seems extremely small for a ported box...

Would 1.25 cu ft be good? what should I tune it too? ~34hz?

i would do 1.75, the way i see it the bigger the better. and yes 34 hz is pretty good. it is a nice blend between sq and spl

the biggest box you can (within Alpine's guidelines) and tune to like 28 Hz

the biggest box you can (within Alpine's guidelines) and tune to like 28 Hz

isn't that low for type r since they are spl drivers.

I would have to look at the specs ... but the lower tuning freq, the less chance of having a fart box