I used the software at: http://www.accelerator-pedal.com/ported-box.asp
i entered my subwoffer specifications and the software told me that my net box volume must be 1.71ft^3 and a tuning frequency of 29.4Hz. What do u think i must use as a tuning frequency, 29.4Hz, 27Hz..?? the net volume is ok? or 1.5ft^2 will be better??:S anyway i then took these 2 results and either use WinIsd or http://www.carstereo.com/help/Articles.cfm?id=31 to find the minimum port area and dimensions.
For 1.71ft^3 and 29.4Hz i got minimum port area=21.74"^2, if i want to have a square vent the dimensions will be(5x5)=25>21.74 so i am ok, and a length of 41.46". This is an example, everything is ok??? Please need opinions if tuning frequency and net volume are ok, or could i go with smaller values such as(1.5ft^3, and 27Hz)? and what sound difference will i have everytime i lower the tuning frequency?