i have a 15' Q. want a box that will get really loud. recamended size is 2.6- 4 cu ft. @ 28-33Hz. with 12- 16 sq. in. of port per cu ft. would a larger port be better than a smaller one?? i was thinking of doing 4 cu ft. @ 35 Hz. with a 6" x 10.5" port. how long would i need to make the port to tune at 35Hz??

Depending on how many sides of the enclosure you are using (Ill assume free standing) your port would be right at 28" long. 4 cuft net after port and driver displacement. If you use 1 wall, it will shrink down 1-2" in length. 3 walls, shrinks 3".

Thanks,

Scott