I have made calculations for a driver I can get for about 85 bucks. Yes, I would love to get a Shiva instead but for me the cost would be around 200 bucks. I have a 12" sonotube and the driver I can get mounts on a 11" diameter, so I hope it can be done. Here are the parameters: _______________ 12" unit: voice coil diameter : 2½ speaker displacement : 1.98 liters FS: 22 Hz Qts : 0.355 Qms : 12.880 qes : 0.365 Vas : 176.22 liters Xmax 17 mm Revc 3.6 ohms ________________ I don't know how to compare that to those on Shiva (meaning I don't know if it is a bad driver or a comparable one). The volume of my sonotube is 697 liters and the ISD Online Im using is at: http://www.linearteam.dk/newdriver.html I filled the driver parameters, selected a vented enclosure and filled the box volume in liters and the tuning frequency was 16Hz The resultant graph seems good from 20Hz to 50Hz is about -3dB and it have a big bump around the 16Hz of tunning frecuency. The port should be 3" and 27cm long. Is there something important I have missed? Are my calculations correct and I can expect a good subwoofer?? Thanks to all that have helped me to get here (specially to Jack, which always encouraged me, not that I liked specially, to do all that Im doing now).