Originally Posted by Jon S
I had a Titanic 15" in a 21" cube box with a 1000-watt amp... It was way too big for the room... Either way, a 12" Titanic MK III is out of the question... Parts Express is currently out with an expected available date of June 2013. I understand that the 12" Dayton Audio Reference HF sub is supposed to be tighter and more accurate than the HO or the Ultimax which are designed more for bass output than accuracy.
High excursion subwoofers are more effective for low frequencies (such as, below 40hz).
High efficiency subwoofers are more effective for frequencies above that.
So you kind of need both to do it properly.
A HF-12 is a middle-of-the-road solution, the PA-18 is more efficient than it and the HO plays deeper than it; the combination of the two is of course better; hence my recommendation. The HF-12 doesn't do either as well, it's sort-of in the middle. (In this case, you get what you pay for.)
However given your size restrictions you could just select the smaller cone equivalents of the PA/HO (I believe them make them both in 12's).
You'll lose SPL and dynamic range, but you'll save money and space.
You could even downgrade to a nu1000dsp, even less dynamic range and SPL, but saving money.
You will still need some sort of DSP/XO/EQ to make it all work well. Room treatments and correct subwoofer placement helps as well.
Otherwise sound quality will suffer.