Our discussion has gotten way off topic, from are the speakers any good to was the stuff installed and set up right. I know you are just being the devils advocate by asking about other variables. I have seen your system, I know that you know what you are talking about. The main issue is with the subs not the 6.5s so we will take them out of the equation. I am not the type to tweak on things once I have it set up right, and none of the variables you listed had changed same amp, same volume, same gain on the amp, same cross over settings and the speakers did not perform. I know the next question is going to be what were you running: Alpine head unit can’t remember which one, 4 gauge cable, Zero Noise RCA’s, 2 1.0 Farad caps, MTX 1000d (yes I realize that this is not a good SQ amp in the first place). With all things remaining the same even the music that is played, with my experience these Polk DBs did not last. After my problems with Polk subs I went with some MTX 12s instead and did not have an issue.