Well, after looking around the internet for a while i found that the best sounding enclosure for my sub is: "1.25 cubic feet ported that is tuned using a 4 inch diameter port that is 12 inches in length." My questions are... is the displacement of the sub included in the 1.25 ft^3 or do i have to add more to compensate for this. Also, does the port need to be round or will a rectangular port with the same volume work? By the way... its an older Polk GNX104 sub...

 

The displacement of the sub usually isnt included in that 1.25 cubic feet.

The port can be whatever you want. I prefer slotted for ported boxes. So the specs call for a 4 inch diameter port. The area of the opening of the circular port would be 12.56 sq in (pi x diameter). Take that, and translate it into a rectangle, i.e. lets say you want your rectangular port to be 13 inches tall, the width of the port would be 0.97 inches (12.56/13).....such that your surface area of the opening of the port is still 12.56 sq inches. So your rectangular port would be 0.97w x 13h x 12d (the depth of the port wont change). Now if you want to tune the port/box differently, thats a whole other story, and a complicated one, but I hope what I just typed makes sense or helps.

 

thanks for the information... just one question... does the area of the opening have to remain the same or can I change that and change the depth?... I've been thinking of making a 2" x 12" slot that is just over 5" deep (this will keep the volume of the port the same as the one recommended) so will this still work?

 

as long as the volume of the port is the same, you're all good...also, sound doesnt like square corners, so take some sand paper and sand down that square edge and make it rounded over.

i work at a car audio shop, and all of our box volumes are volumes BEFORE the sub is in place...so they do not include displacement of the sub...so you dont have to worry about trying to calculate that