Power hx2 12 box?

You should have no problem with port length with a box volume this large.  Using the Wedge enclosure 2 volume calculator, if you're box material is 3/4" MDF and taking out 0.09 ft^3 for driver displacement, the net internal volume is approx. 2.9 ft^3.  If this box has bracing, deduct those displacements.

Here's a calculator to get you started.  You can find what the minimum square inch opening of the slot will have to be by filling in the top calculator.  I'm guessing about 37 to 40 sq in.  After you find that, design your slot, giving it a width and a height.

This is where I can't go further because I don't know if you have the driver mounted on the slanted (hypotenuse) side of the box or not.  Whatever side it faces on, I would suggest building the slot port along the bottom of the enclosure where you have plenty of room to work with.

With the width being 26", and two side walls of 3/4", the measurement inside width would be 24.5".  If you were to use that entire width you could use a rather narrow slot...but that calculator will pop up a warning box that tells you that you should keep the slot ratio less than 8:1.  Work with that and design the slot dimensions.  Put all your data into the second calculator and it will give you the length to build the port.

After you do all that, and this is important, you have to figure out the displacement of the port structure (the walls and airspace that the port steals from the box volume).  Deduct that displacement from the 2.9 (or whatever you had figured) cubic feet net volume that you originally entered into the calcuator, and do it over again.  You should find that with a net volume this large for one woofer, a tuning freq of 40 Hz, and slot opening of about 40 square inches, that the port length should fit easily along the 23" bottom of that box with plenty of room to spare.

Here's one slot design that I figured, just as an example:  You build a slot opening centered on the bottom of the box that has an internal opening size of 16" wide and 2.5" high.  You make it out of the same 3/4" MDF that you built the box with.  To find displacement, you measure that whole port structure, which will have a 3/4" wall on each side and a 3/4" top, times the length that the program tells you.

The calculator gives you the length based on the box volume of 2.9, which comes to about 10".  You find that volume (you can use the rectangle box calculator on this site) and find that it displaces .3 ft^3.  Deduct .3 from the 2.9 and re-enter 2.6 in the calculator.  Now, when you press calculate you will see that the port length has grown because the box air volume dedicated for the sub has gotten smaller.  Now it's 12.7" long and you have to figure port displacement over again.  Make another adjustment to the box volume, and do it again.  You have to do this over a few times until you nail it, or quit!

In this example, I finally came up with a 16" X 2.5" slot opening along the bottom of the box and a port length of 14.25".  The air volume that is left for the subwoofer is 2.45 ft^3.  This is a tuning freq of 40 Hz.  The port structure is built with 3/4" MDF and centered, with it's own top and side walls.  There is 7" of space at the end of the port inside of the box, which is plenty.

Give us feedback on what you come up with.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

stevdart thanks for the reply here is a little more info that I hope may help you and me.  The woofer is getting mounted on the front slant which will face towards the rear of the trunk.  I have figured that the box should have a volume of 2.67969 cubic ft.  I got that calc by using the rectangle calc. with the dimensions of 26" W x 15.5" H x 10" D.  Which gave me 1.68721. Then I added two of the Wedge 1 calc. (one for the front of the box and one for the back) with the dimensions 26"W x 15.5" H x 6.5" D that gave me .49624 add those together and got the volume above.  Found the speaker displacement to be .127 cubic ft from Rockford so the total without the port is 2.55269.  Then I went to the calc that you also said to use for the port and found the min. area to be 41.63".  Now for the problem I am not sure yet if I will be able to put the port on the bottom because of an amp rack that may be there. I am waiting for my buddy to get back to me about that. So I was trying to put the port to the side of the woofer which when I try to get a port with the min. area they all seem to be a little long for the box.  I can modify the box to a wider width at most I have 37" between the towers in the trunk. Any help would be appreciated.

I just talked to my buddy and he says that it will be okay to put the port on the bottom of the front panel. Now I need to figure out how high I can go on the port with both on the front. I have figured that I will have  15 1/8" on the front panel to work with after I subtract the top and bottom thickness. The Hx2 sub's outer diameter is 12 17/32" according to Rockford. That will leave me with 2.59375" to work with for the port height. I think that I will try 2 3/8"H x 18"W but I don't understand the difference between the slot and the square port  can you help?

I used the wedge 2 calculator for this box so that the walls are figured correctly.  If you use the wedge and rectangle calculators you should use inside measurements and then input '0' for thickness.  That's so that wall thicknesses won't be deducted that aren't there.

http://www.1728.com/pythgorn.htm is a nifty calculator that gives you the slanted (hypotenuse) side of a right triangle.  The right triangle you are working with is 15.5 high and 13 deep (23 - 10).  If you input those numbers in the calc you get a hypotenuse of just over 20".  Take off 3/4" twice and it is 18.5".

Oh, and a slot port is same thing as a square port.  A rectangle as opposed to a circle.  Rarely will you see an actual square port...I've never seen one, because if you have the room for a square you would probably have the room for a circle of equivalent square inches.

I don't think we are on the same page. Because I have cut out the sides already and I can physically measure the hypotenuse or slanted sides and my tape tells me that both the front slant(front of the box facing toward the trunk) and the back slant(back of the box that faces toward the front of the car or at the back of the rear seat) are 16 7/8" from top to bottom. I think that you  missed in my first post that this is a trapizoid and not a wedge like the wedge 2 calc that you are using.

Okay, then you're well on your way.

BTW...the wedge 2 is a trapezoid.  See https://id.mind.net/~zona/mmts/geometrySection/commonShapes/trapezoid/trapezoid.html

This is one of those situations where it's true that a picture is worth a thousand words.