Sealed will let you run the smallest box size. It will lower your output by 3db or so but it depends what type of system you are going for. Think if you want to sacrifice spl for box size. Those two 12s will still pound in a sealed box. In fact the type X are better designed to run sealed. So if you have a big load of power to give them I would go sealed. If you have a weaker amp I would still go ported. Go to the alpine's website and download the manual for them, they give dimentions and stuff for the boxes.

I was going to get a type-x but after reading reviews it seamed like everyone was going sealed with them because of their design. I had the room and wanted to go ported to get the most spl so I didnt get them. But if you want to go sealed to save room then you have great subs for that.