I have a 12'Shiva driver in a 157l volume sonotube. I have a 4'd port that is 12.5" long and flared on both ends. My problem is that I keep bottoming out the sub.What are my options. If I tune to lower frequency would that stop the bottoming? How about plugging the port. I think it is tuned to about 20hz now. Any suggestions?What ever happened to the Maelstrom driver?