Using the 8 Pi external dimensions I've subtracted 1.5" from each dimension (2*.75" material) to arrive at the internals.

1) I calculated the front "cube" portion of the cabinet first:
24.5"W x 30.5"H x 9.6"D = 7173.6in^3 or 4.15ft^3

2) I calculated the rear "trapezoid" portion as (A=h/2(b1+b2))*Height:
(5.25/2(12.5+24.5))in^2 x 30.5"H = 2962.3125in^3 or 1.714ft^3

3) Add front and rear portions and get 5.864ft^3 total internal before subtracting mid-horn or bracing.

4) I estimated the mid-horn flare w/mounting plate to be about 1.12ft^3 and the driver to be .043ft^3 totaling 1.163ft^3.

5) Subtract 1.163 from 5.864 and total volume remaining is 4.701ft^3.

6) I only subtract 5% for bracing giving 4.466ft^3 total internal volume.

According to WinISD, using 3 ports (1.625x3.5 as the plans suggest) this tunes a 4.466ft^3 cabinet to 62hz with a F3 = 50hz and a 5.4dB peak at 70hz with the Alpha 10. To get a flat response to 40hz WinISD says the ports would each have to be 4.43" long.

Am I still calculating something wrong? Is WinISD's vent calculation inaccurate (seems I read that somewhere)?

Wayne, if you're bored (you have to be if you've read this far ;p) and enjoy toying with the mathematically challenged I still appreciate your help and now your patience. ;^> Sorry, if I'm beginning to aggravate. Just trying to grasp things before I make the plunge.

Thanks,
Jeff