I was thinking about a few of the subwoofer systems ive had in the past and one stepped out to me it was a four cubic foot box cut down to 3.45 cubic feet anyway in the 4.00 cubic foot box it had two 4 inch pvc ports 10 inches long which gave it a 36 hz port tune according to linearteam (and it did just that in my car) but when the box was cut down to 3.45 giving it a 38.8 port tune .....but when we got the subwoofer in the car it tuned out to 40 hz without question......anyway what im saying is I believe the demensions you make your box and where your ports are can change your port tune....and this didnt seem to be a case of where the box was sitting and how close to the trunk wall it was sitting