good subwoofers

Disclaimer: I'm a noob to this website, so forgive me if I make some mistakes. So my current setup is as follows: A Memphis C3 12" (dual 4ohm) powered by a Memphis SR.500 in a custom ported box tuned to 32hz. A Kenwood Excelon Head Unit. Memphis MC 5x7's powered by a Rockford Fosgate Prime...