My new-to-me 820s

[wws944]

IIRC, all of the plans are missing some information and/or has some way wrong dims, so do require a bit of common sense and/or speaker design knowledge to make them 'good enough' once the vent is properly tuned and the damping done to 'taste'.

Figures...

The 820's vent is hinted at though in the far left 3/4 view where a corner of its framing is shown and its 2-1/4" vertical cutout height is 'hidden' in the section B-B view; so with the implied 5/8" thick side base rails framing the cutout, its width is = to the horn width of ~28-1/8", making the vent area ~63.28"^2 and the 3/4" thick front base rail makes it 3/4" deep. The exposed center brace creates a minor vent divider that combined with the cab's high aspect ratio, multiple vent holes, fiberglass damping and grill cloth shifts tuning lower than typical reflex Helmholtz theory predicts.

If you look way back at the first photo in post #1 of this thread, you can see the 'thin' edge of the vent. In the picture, it runs diagonally from one side of the cabinet to the other. So it is several inches wider than the bass horns. And yes, it has that little wooden block in the middle of it. Funny - I simply thought the wood block was for extra stability, and never knew it was also part of the vent tuning. Learn something new every day!

Hope you’ll publish your cab’s vent dims for posterity though and eventually measure actual tuning of each in a corner.

Will be happy to do so.

Speaking of which, I do have a question: my living room has hardwood flooring in it. Should I make up a triangular-shaped piece of carpeting or similar for them to sit on to help damp any cabinet resonances? We were musing that Altec may have made that assumption.