I have been using an Infinity 1230 for a year now in our convertable. It is in a ported box built to Infinities specs. I am running a clean 200 watts to it. It sounds awesome and plays plenty loud. I say operator error in the sub failure. I beat on mine prety bad (it's always cranked up when the roof is down) and it is still in perfect condition.

 

Oh and I don't have a subsonic filter either.