Tuning an enclosure?

No it will be able to play below that frequency but the response will be reduced because of the rolloff.

Check this picture for an example. Those are a few different response curves, different tuning frequencies will offer different peaks. Generally when you tune higher you get a larger peak which is good for SPL competitions but you rolloff faster so you miss the low end.

In short, tuning is a function of port area and length in relation to the volume of the enclosure after all sub, port and bracing displacements are removed.