Right, so you're interested in volume than SQ then?
Basic points....
- ported gives more volume, sealed gives better SQ.
- If the ported box is tuned to a lower frequency, you get better SQ, higher frequency, more volume. I'd go for somewhere between the two, around 32/33hz.
- the tuning of your enclosure is dictated by the volume of the enclosure and the size and length of the port.
If you want to run a ported twin 15'' enclosure, it will take up your whole boot. If you're cool with that then crack on!
Did you get the instructions with the subs? If you did, have a look see what enclosure volume they recommend. Then stick that figure into an online calculator to work out the port size you're going to need to tune your box to the desired frequency.