Normal
If you're going to go through the hassle of designing and building your own subwoofer - please for the love of everything good - don't limit yourself right off the bat to old technology! If you want that exact subwoofer - just find some used and buy them. If you want a great sub - ask around here, get some great drivers (neodymium, high XMAX, from B&C, Faital, Eminence NSW, etc), model them in whichever software you are most comfortable with, ask questions here, then build them. You'll end up with better performing subs for similar cost.