"Extended Bass Shelf" aligned sub then. Had a look around the web, think I understand(ish) the principle. Design a box to go with the intended driver, for a flat response, then upsize by 60-80% and tune the port - sounds simple. So spent awhile putting meaningless (to me) numbers into a spreadsheet (for fs, Qts, .....) and get out some equally meaningless numbers and plots, but get a box internal volume of 3.9cu-ft, so x 1.7 = 6.63cu-ft. Then calculate port dimensions (not looked into this bit yet) build box, attach plate amp and connect. Is that about it?Or would it be better to upsize the basic 4 Pi cab by 80%? I have to say I'm not really into this "design it yourself starting from scratch" stuff and am always happier to use someone else's (who at least knows what they are doing) tried and tested design ![](http://www.audioroundtable.com/emoticons/winkie.gif)
Paul W.