Could someone please explain what tuning is? ( all i know is that its got something to do with a PVC pipe attached to the port?) but anyway how would you secure such a pipe to the box? what do you mean when you say tune the port to 35Hz?
U can make a port square as well. Usually easier too. A port reinforces a certain area of the band with. If a port is tuned to 35 htz then all most of the outout of the subs will be though the port when playing frequencies in the mid 30's. Ported boxes are able to yield more output at tuning then a sealed box would at that same pitch.
LV= [(1.463 x 10^7 x R^2) / (Fb^2 x Vb)] - 1.463xR Use the above fomula to determine vent(port) length. Fb - is the desired tuning frequency of your enclosure in Hertz. Lv - is the length of your port in inches. R - is the inside radius of your vent tube. Vb - is the internal volume of your enclosure in cubic inches. To convert cubic feet to cubic inches, multiply by 1728. If you want to calculate square vents, the formula below will give you the value of R to use in the formula above. R=square root of ( A / Pi )