If they are wired out of phase with each other they can be used in a magnet to magnet or cone to cone alignment to create an isobaric subwoofer. Another vote for the Dayton RSS315HF-4 here. I've got ...
The amp is on it's way out in my Paradigm PW-2200 V2 sub. Waiting on pricing for a replacement amp from Paradigm. If replacing the amp is more than 40-50% of what I paid for it I'll probably put it ...