I built a pair of these subs but the output was just not enough. I can see how with four it may be great but I don't have the room for them. I also found that they were easily pushed to much and would get "funky" but that's on me.
I will say that I ripped out the drivers and put them in some 0.5ft^3 cabs tuned to 45hz and they rock! So I would caution anyone looking for medium to high output. That said they would make a great computer sub sitting next to a desk.