Started considering 18" mini-devastator (maybe the Mini 18 Stepped Version 3 Flex Tune) out of my existing driver (upgrade existing sub), Fane Imperium 18NDXL, 29.4^2 / 5.6 = 154. Fs/Qts = 110. I have it currently in 136 liter bass reflex tuned to 24 Hz EQd straight to 24. Later maybe NSW 21 Dev, but could try the old driver first if not bad idea.