Might as well start a thread before I start the project. It gives you all a chance to help me! This sub is intended for .1 channel as I think I am happy with my front main speakers (medium size Linn Index) although I guess that might change after I experience some proper bass. My sono-tube-sub will be very simple. A passive design with downward firing 15" driver and port(s) at the top. I'm going to keep the tube at 510 internal diameter by 1200mm. This gives 240l volume. So this staring point is basically an SVS 20-39 but 25% bigger in all dimensions. 1st question: What should I tune it to? winISD suggests that between 17Hz and 21 Hz is OK with 1 port. Or should I have more ports and go lower? Are really long ports OK or is there a sensible limit that winISD doesn't inform you about. eg in my 1200mm tube is 500mm sensible, is 800? Also winISD only offers up to 140dia port - is there something wrong with going above that? what's the upper limit ? 2nd question: Which driver? Adire Tempest is very well thought of at $150. I also found the dayton titanic mkIII at $200. I can pick up either in the states and the price difference is acceptable. The performance on winISD is more or less the same, tempest better if anything, so apart from sexier looks (which you won't see) the titanic only has more Xmax in it's favour. So what does 20.5mm versus 16.4mm do for me? 25% more air movement before bottoming I suppose? so what does that mean in terms of max output I can drive it to? 3rd question: Am I doing it all wrong? I just picked a 12" driver at random in winISD and got the ACI SV12 which just happens to be $140. It kicks the ass of the 15" drivers in my 240l enclosure. Is a 15" only going to outdo the 12" and silly levels? How do I calculate when a 12" will conk out and a 15" keep going? All help appreciated.