My original calculations had called for using a 20" tube for my Tempest sub. I have been hard pressed to find a place that sells 20" (I finally found a place an hour away) and even there I have to buy a 12' piece for $104.00(which will be good if I ever make a second sub). A place right down the street from me sells 18" tube at a good price. By using the 18" tube, my sub will shoot up to 5'4" (without legs). I know there have been concerns on here about standing waves and taller subs, is there any concern for a sub that tall? Also I plan on flush mounting my amp much like Warrick did with his. My calculations show that flush moutning a PE 250w amp will cause the back end of the amp to "stick into" the sub about 6" of 1/3 of the tube. Will this affect how the sub operates? Could the amp help "break up" any standing waves in the tube? PS. I have no personal preference about width/height..just want it to sound good.