Which enclosure for Altec 409-8B

[edlye]

Hi, I'm very new to diy loudspeakers and am interested to know if anyone has an idea of which enclosure will suit an Altec 409-8B. The Qts is 1.54, Fs is 91Hz and Vas is 0.61, the speaker was originally designed as a ceiling speaker. OB is not an option because of the lack of WAF. Many thanks!

[tubewade]

I would have suggested an OB, probably, but since that's not an option, how about an aperiodic? That high Qts is going to be a killer and your first concern will probably be trying to tame it. You may have to install a damping pad over the back of the driver. I assume that if the WAF doesn't allow for open baffles then a huge 6 cubic foot infinite baffle cabinet would be out of the question too.

Best, Wade

[edlye]

Seems that OB is quite an inevitable choice, what are the options to consider? What about BLH or transmission line? Thanks!

[GM]

Greets!

Hmm, these specs are what's listed for the 409-8D, so don't know how accurate this will be, but a ~aperiodic TL is pretty forgiving, so worth a try since it's simple/cheap enough to get a near IB response in a relatively small footprint:

L = 53.183"
W x D = 131.28"^2

All dims i.d.. For WAF, place the vent on the bottom rear, which will have the same 131.28"^2 area. Driver at extreme top and add stuffing until it sounds right to you. Since the driver is going to be up around 49" off the floor depending on how thick a material you use, you may need to make a wedge mounting plate to angle the driver down if you sit fairly close. It's Qts is high enough that a lossy material can be used, so no high $$ plywood/whatever required.

Sim assumes a 1 lb/ft^3 stuffing density using polyfil, so the same amount of acoustic fiberglass insulation will damp out the rest of the ripple.

GM

[tubewade]

I agree with GM. Cheap enough to try and would likely work well. That's what I'd try first.

[edlye]

Imagine my horror when I converted the measurements to metric: 3.33meters x 1.35meters^2. My wife will toss me out of the house if I had that in the living room.

[tubewade]

Wooops! I'm sure she would! There was an error in the math. It shouldn't be that large. I think he meant 135 cm tall with a base foot print of 29.1 by 29.1 cm (847 square cm). If that's not what he meant then GM may to have to elaborate a bit to help my density.

Best, Wade

[Geoff H]

Pity about the WAF - OB situ, they go quite well with a bass helper.

Geoff

[GM]

Originally posted by tubewade
I think he meant 135 cm tall with a base foot print of 29.1 by 29.1 cm (847 square cm).

No, you got it right, just add the material thickness to all sides. It's just a relatively tall column that can be square, rectangular, whatever since it will be stuffed enough that its shape won't be an issue. Indeed, it's aspect ratio is such that it will need to have wide 'outrigger' mounting legs to make it stable against being accidentally tipped over.

[GM]

Originally posted by Geoff H
- OB situ, they go quite well with a bass helper.

Agreed, and its Qts is high enough that the baffle doesn't even need to be all that wide if a decent wide BW woofer is used.