17-5/8"W x 12-1/4"H x 7-7/16"D1 x 5-3/4"D2
First, find the average depth measurement:
7.44 + 5.75/2 = 6.6"
Converting the rest to decimal (because it's easier on my brain, lol)
W = 17.6
H = 12.25
and the average D from above =6.6
Multiply all of that together = 1423
Divide by 1728 = 0.82 ft^3
I rounded up or down a small amount. If those are outside dimensions, you need to subtract the thickness of the material to determine the inside dimensions. T tune to 40hz using a 3" diameter round port, the length would be about 12.5" long.
Edit: too late, lol