Box design for 15 memphis M3

I am planning on making my own box for a 15" M3 subwoofer. I used the program WinIsd and was able to come up with a vented box being 2.464 cubic feet, being tuned at 28.59hz, the square vent being 4.02 x 4.02 inches, and the length of the port being 18.22 inches. I have never built a vented box before and have seen pics of the vent being under the subwoofer on the same side. I need some help on the demensions of the inside air space and i dont know how to make the vent hole and what is the extension inside of the box for the vent made out of? I dont even want the vent being a square shape but a rectangle that is as wide as the box. Can someone clear things up for me? THANKYOU03 F150 on 24's

HU:Pioneer DVD5700

Frt:MC57

Subs:(12)S12L7

Amps:(3)KX2500.1's, MC-2004

I dont think that changing the dimension of the port will make a difference in the resonant frequency. That being said, the area of the opening should remain constant. The are must remain 4.02x4.02=16.2 sq-cm. So depending on the width of the box, just make sure the height of the opening will make the area 16.2. In other words, if the box is 12 inches wide internally, then the hieght can be found by: 16.02/12=W where w=1.335 inches. The vent hole should be made out of wood. Be sure to take the dimensions of the wood into account when calculating for volume. I hope this helps.

you can contact memphis and they will give you the right demensions for the box as well as give you instruction on how to build one. call their customer service or visit them online memphiscaraudio.com