I have 2 Assassin Series 8's I need to know how to make the port and how big. The box I have a pre made it is this http://www.millionbuy.com/hbx8antcm.html

its .51 cubic feet any help would be great

You need to account for the port displacement... and you'll need two 4" ports.

In other words, that box won't work for a ported application.

Yep, not even close.

it says on the web site it has to be in a box tuned to 33 hertz in a .5 box and mine is a .51 a touch bigger and it says .05 dispalcment so i guess how is it to small i can port it from top down

i havent even looked at the link but if it says that it needs 0.50 cubes ported at 33hz, with 0.05 displacement, then you need a box that WILL BE 0.50 cubes AFTER the sub and port are installed in the box.

Now, you can port outside the box but it will look extremely goofy. We are talkin about a 3-4" port diameter running between 36"-65" long...

I don't forsee this happening.

i am inverting my sub i just need to know what size the port has to be

Can't fit it in the enclosure.

You can do an external port, that will be your only choice.

This might help. This box is .6cuft tuned to 29hz, external dimensions are MORE than 3.5cuft

umm not to be a dick that don't help i just need to know how big to make the port weather it is external or internal

for a 4" port - 58.25" long. Non flanged(like using pvc pipe the whole time)

for a 3" port - 32.25" long. Non flanged(like using pvc pipe the whole time)

If using a square\rectangle port lengths are as follows for port areas given-

8sq in - 36.25" long

9sq in - 41.50" long

10sqin - 46.00" long

Port lengths get astronomically long when being designed for small Net-ed enclosure sizes when required to be tuned low at the same time.

http://www.carstereo.com/help2/Articles.cfm?id=31