Guys, thanks for posting! For a point of clarification the Sonotube is a ported design. I downloaded a program, Sonosub, that had a Fi Q18 as a default driver and it had a suggested total volume of 260 liters. I tried to paste in a pic, but was not successful. The other parameters the program suggests are: Tuning Freq - 15.6hz Inside diameter of Tuber - 22inches Port Diameter - 6inches Port Length - 30inches Endcap to Endcap Height - 48.7inches Of course the height and diameter can be changed to meet the Volume requirements. A couple of more generic questions. Is there a book that I could read that clearly explains the driver parameters and their effects on real world performance? Such as Vas, Q, etc. Impious you seem to have a handle on them. The other question, Impious, you mentioned running a simulation on the design. Is there software that would make that easy, and free ? Again, thanks Guys...