Bass Equalization Circuit: Good or Bad Design??

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.

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.

Almost every powered sub has one. It extends and flattens the bass output. But, the sub needs to be designed to work with it. For a small sub to work well it needs EQ. a large amount of speaker excursion and lots of power.