.88,1.25,1.50,1.90ft3 are actually the most common box volumes for the 12" subs from most of the major box makers create. Same differences for the 10's, they use the "popular" sizes, Mostly cause the mainstream subs tend to work in those ranges. 34hz is the most common tune frequency for universal's, 38-40hz is the most common for pre loaded enclosures...generally speaking. exceptions for preloaded being Polk db12 is 32hz, Infinity 34hz and i think MBQ is 34hz. RF is 40hz and i thnk kicker is too.
Q-logic boxes are 34hz, except their bandpass witch is 40-60hz. AtrendUSA are 32-34hz, Sound Ordinance is 34hz,BX is 38hz, Khaotik is 32hz i think...they make some wicked boxes.
Prefabs are fine as long as you check the sub specs then look for a prefab that matches, most of the time its not too hard to do...its also not hard to modify as needed, you can add bracing to lower FT3 and cut or extend the port easy enough. Most in general make really solid, well designed boxes, its just you choose the sub first, then the box to match. But the OP is now in a position where he will either choose the right sub for the box or use a different box for his selected sub.
