I didn't know whether to ask a dual sub question here or not, but since it came up, I will. :-) I have a room that's 21'x12.5'x9. I have BA VS line with 4.5" woofers and a 5.25"CC with PB12NSD. I was thinking of adding a second PB 12 NSD, but I don't know if it's really needed. The room shake during the Underworld Awakening scene in the new coven with the giant Werewolf first appearance. Will I really gain that much with a second sub?