Question about calculating box angles

sure-fire, huh?

http://www.gomath.com/geometrycal.html

I don't have any subwoofer specific links but this should give you a little geometry review.   And no, I'm not making fun... Short of using a cad program to do the design, getting out the ol pencil, some grid paper, and a calculator is the easiest sure-fire way to get the lengths/angles right.

What type of shape were you looking to build? 

What are the dimensions you know for sure (height?, bottom length?, etc.)   Are both sides going to be angled, or just one?

https://www.the12volt.com/caraudio/boxcalcs.asp   this should help you get a rough idea

The thing to do is to think of the box as a sum total of rectangles and triangles.  Draw a sketch of the box design, showing the angle.  Draw a single line out of the bottom corner to represent the 3rd dimension of the box, the depth.  Put in the measurements (in inches) of all sides shown.  For example, a square representation would show measurements for 4 sides and a 5th measurement for depth.  A box with one cut-off corner would have 5 sides and a depth, and a more intricate box might have more sides than that.

Now draw straight lines across that sketch to divide it up into rectangles.  For a box with one cut-off corner, you would have 2 rectangles, and the piece left is a triangle.   So you have 3 separate "boxes" to figure.  Find the cubic area by multiplying width by height, then multiply by the depth.

The triangle is figured differently.  The width here is called the base.  Use 1/2 of the base times the height at the highest point of the triangle, then multiply by the depth.  (shown like:  1/2 base X height X depth) This will give you the volume of a triangle.

Add up the three totals you came up with and you have the interior volume of your enclosure.  And you know then to divide that number by 1728 to arrive with cubic feet.

If you draw your box design as you read this, you'll see that it makes it much easier.  And never mind what side of the box the speaker will be positioned.  It's just important that your sketch shows the angle.  Hope this helps.

https://www.the12volt.com/caraudio/boxcalcs.asp

Wedge Enclosure 2

http://www.1728.com/pythgorn.htm

here yah go.  quick google search