Can someone double check my math?

[cradicg]

I am getting ready to build a box for my JL Audio 8w7. The sealed box specs say to use 0.875 cubic feet, not including braces. All materials will be 0.75 inch thick MDF. So here goes....

0.875 cubic feet is 1512 cubic inches (using online calc) right?

Using 11.5 x 9.5 as my INTERNAL width and height, I need to figure the displacement of two braces. This sub is 17 pounds and moves a lot of air, so over bracing is better than under bracing. I will cut two solid 11.5 x 9.5 sheets and then saw out the inside. That will leave me with a 1" ring. So a 0.75 MDF sheet cut to 11.5 x 9.5 and then cut again to a 1" wide ring will displace 28.5 cubic inches right?

Since I am using two braces, that gives me an additional 57 ci of displacement added to my original 1512 for a total needed volume of 1569 ci.

Having established my internal width and height at 11.5 x 9.5 inches, I will have 109.25 cubic inches of displacement per linear inch. 1569 divided by 109.25 should give me an internal depth of approximately 14.4 inches. Does this sound right?

So my final internal dimensions will be 14.4 x 11.5 x 9.5. This will give me a total volume of 1573 ci with a final volume of 1516 ci after the bracing is installed. Just a hair over the original figure. I think I want to make the braces a bit thicker so I may adjust the L x W x H figures to accommodate. I am more concerned about the math method being correct than anything else. It is late and I haven't done this for a VERY long time.

Thanks!

 

[Taranis]

remember to adjust the box dimensions for the size of the magnet. Also, a couple of cubic inches up or down really isn't going to matter, especially in a car.

You can always download WIDISD to play with box sizes.

 

[Infinity]

Just use a 1 cube box, add your speaker and bracing, and 1 pound of polyfill. It will be so close that you won't even be able to measure any differences electronically. On a sealed enclosure, precision isn't key, but bracing and a good seal are.