I have a hysterically well sound proofed, small bathroom in my cabin (around 6x7 feet, 7 feet high ceiling) with a pair of JBL Marine 6x9 speakers mounted in specially made boxes in the ceiling sound proofing them towards the other rooms. This was really the only way to place speakers because of the rooms limitations. And the speakers had to be able to withstand the moist from showering and I have several of those in other ceilings, they sound pretty good! The problem is that they do not give me the deep bass I want (I demand good sound, even in the bathroom in that cabin, probably the only cabin in town with a 11.2 surround system with dual 15" subs!), so I'm going to supplement that with a subwoofer. There are placement problems with that as well, it can not be wider than 8 inches, or 20 cm. Oh, and it has to be white, of course!
1. Buying a Q Acoustics 2070Si with dual 8" drivers and a 140 watt built in amp.
2. Build a box myself (I have done several for cars before, so I'm rather a pro with that) and use a 10" or 12" shallow mount sub, like the Alpine SWS-1043D, which I already have.
I don't really care about the higher price on the Q or the work I have to put in on the box, all I care about is that I get "dry", punchy bass. The music is mainly going to be heavy metal when I'm in there, or my son is there, or whatever's topping the lists at the moment when my wife or my daughter are in there. So what would be the best bet on this? Buying the Q and building the box and then keep what's better working is of course an option, but if there is a consesus in what would work best, I could save myself for the extra trouble.
Oh, the car subwoofer would probably take the moist (which is a lot less down by the floor, but still...) better, but replacing a sub every five or ten years to keep the best sound is really not a problem.