I have no problems with the quality of the Bass with the Seismic12 its a great sub, but 2x I had to replace the amp due to it producing a loud hum (I know I can't escape it LOL) In the case of the sub its was the actual amp and not caused by any ground loop or other issues. Its funny even my dealer, who has the sub, is experiencing the same problem, only worse. Granted Paradigm only charged me $75.00 out of warranty + Shipping, but it is a huge pain in the *** to have to unscrew, and disconnect the amp portion, very carefully package it, and wait 3-4 weeks to get it back each time.
I love it's small footprint and it shakes my HT room by itself, but quality has been a problem for me with it. That's why the PB13 Ultra is probably my leader at this point, but still torn on dual subs.