what's the advantages / disadvantages of sealed or ported, down firing or front firing.
A vented sub gets a extra efficiency at the bottom of its pass band. In smaller, closed rooms, the natural rolloff of GOOD sealed subs can work better because the pressure vessel gain seems to match the rolloff of the sub. In larger/more open rooms, the room gain tends to mate well with lower tuned vented subs, so the added efficiency is a big plus. However below the tuning point, it rolls off much faster than a sealed sub.
I recommend never getting a sealed sub smaller than the surface area of 15" driver
with long throw. Else it'll be too punchy and distorted for accurate reproduction, as it'll too quickly hit its limits on deep bass. Most sealed subs have circuitry that cuts off the low end at high SPLs, and you don't want that.
I also recommend never getting a vented sub smaller than a 12" with a reasonably large box, for the same reason. Also, if a vented box is tuned too "flat", the room will add a lot of extra deep bass. For music this can mean a perception of "slowness" because, after all, a 30hz tone
is slow compared to its harmonics IE 90hz. So you need to equalize appropriately.
All the above said, in your budget I recommend the Rythmik FV12:
http://www.rythmikaudio.com/FV12.html
