I just went with a width that fit into the space I have available. I never even bothered to calculate the LF cutoff because I'll get what I'll get anyway - I just made them as wide as possible:-)

"How will you do the x-over? Are the PT2s open back? Will you use a notch filter for the pt2 driver?"

I'm actively crossing them (3-way) triamped using an Outlaw 7.1 amp and an Ashly XR2001 XO. The whole affair is open back and the PT2's are sealead anyway. They're monopole so open baffle or sealed won't make any difference.

I don't plan on any notch filters or BSC at this point. If anything, I'd consider a notch filter for the mid drivers. They have a nasty peak between 7-10Khz, but I'll probably end up leaving the XO point somewhere between 3-5khz. More than likely (hopefully) it'll be a non-issue.