The top cabinets are a little more than 2.5 cu. ft. in volume and built in a trapezoidal shape. I used 1" thick super refined fiberboard. It is quite expensive but not too bad to work with, and is really good stuff! The cabinets are designed using a 5.7 degree taper and to not have any parallel sides, except top and the bottom. This design insures standing waves in the box are kept to a minimum. The front baffle of the lower cabinet is sloped, and the rear is not. The front baffle to the top cabinet is not sloped, while the rear baffle is. The overall outer dimensions of the cabinets are 24" deep, 20" wide at the base of the lower cabinet, and 21" deep and 14" wide at the top. The lower cabinet is 30" high. The top cabinet is also 30" high, but 14" wide and 21" deep at the base, and 8" wide and 18" deep at the top. I used liquid nails and wood screws to hold the boxes together, and silicone to seal the joints.
EQUIPMENT USED I have a Sears plunge router and a Jasper 200 jig to cut all the holes. To do the angles I used a portable table saw, and to cut the wood a Skil saw. It is not the best of equipment, but every piece fit pretty well, and what didn't, I trimming up with a vibrating sander. I will eventually paint them, and hopefully get a nice finish.