I purchased the Parts Express 10" Titanic driver and 150W amplifier. I put them in a 2 cubic feet enclosure with 2 2 inch internal diameter ports 10.81 inches long as specified by WinISD. Since I was so excited about building a DIY subwoofer, I neglected to break-in the driver according to the instructions provided by Parts Express. Now that I've finished the sub and am starting to test it out, I'm noticing that it bottoms out like crazy. Now I am fully aware that the ported design has a much higher tendency to bottom-out that a sealed enclosure, but this is ridiculous. But then again, I'm not exactly sure that it's actually bottoming-out. I've read that when a driver hits its excursion limit, there's a sickening whack. However, the sound I'm experiencing is more like a light pitter-patter of wimpy whacks. The volume on the subwoofer amp is set pretty low, only 1/3. Anyone have any idea what I might be hearing? Have I somehow damaged the driver, or is this merely a side effect of the breaking-in period that will disappear shortly? Or perhaps the driver is underpowered and the amp is clipping? (I've already double checked to make sure the driver frame and port tubes aren't just vibrating, also, plugging up the ports tones down the problem a bit, which is why I suspect it's bottoming-out) Any comments would be greatly appreciated.