i am soon going to order a Fi Q 10". I'm very new to building the enclosures so i was messing around getting all of the dimensions right for my truck in Winisd.....but when it came down to the vent length, i do not know what i am doing at all...i selected a cylindrical shape and it said that i needed it like 44 inches long at 4 inches diameter...what am i doing wrong??... help would be greatly appreciated....is this when i use like a rectangular 4x10 port of something?