Rwwear is correct. It is impossible to get deep bass out of an average size subwoofer without some sort of bass equalization, i.e. boost. I once built a sub from some plans in Audio magazine that used an 18 inch JBL 2245H in a huge ported box (48" x 36" x 22") and they still recommended equalization to get it flat down below 30 Hz. I used it with DIY summing crossover and a Phase Linear 500B (500 watts/channel into 8 ohms) bridged to mono for 2000 watts. It worked real well except that the amp would blow up a lot. I guess that's why they were called Flame Linears.
Then I got married, and well, you know the rest of the story.