Considering Enclosures for pair 421-8H

I have found some good information from this community, so first a thanks! (I posted in A-L Users Community first - but this is where the "Altec" action is, apparently.)

I have (2) Altec 421-8H drivers that came in an unsatisfactory enclosure. My interest is to install in appropriate enclosures for bass guitar and LF for theremin, and miscellaneous LF instrument support.

The box they came in rattles and hums badly. It sounds best with the back removed. My goal was to make an 816, or 817. Then, I found a couple of vintage Carvin combination enclosures for 15" speakers. They are rough, no drivers, handles or terminals, but can be obtained more easily than making new. Dims (outside): 28" w x 31.5" t x 24" d

As close as they are to the Altec combination designs (825, 816) I'm thinking they should be worth trying. Any comments are much appreciated.

Thanks, David

They should work. I recommend putting the interior dimensions into a modeling program to come up with port size.

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Originally Posted by Old Guy

They should work. I recommend putting the interior dimensions into a modeling program to come up with port size.

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Thank you, sir! That is all the encouragement I think I needed to try them out. Just need find terminal cups and handles. Any inexpensive sources lurking out there?

The existing port(s) along the bottom are flared to a 7 3/4" tall x 13" wide (each). Is the "port" size the smallest opening at the back of these? It would be easiest to fill in to make the port smaller, but as a flared horn shape, I don't know how that affects the port's calculated size /area and length.

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Originally Posted by everydaylight

Is the "port" size the smallest opening at the back of these? It would be easiest to fill in to make the port smaller, but as a flared horn shape, I don't know how that affects the port's calculated size /area and length.

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No and don't; truly flared has to be calculated based on its flare frequency and factor whereas a parabolic flare's [one side pair parallel] mean can be calculated using the end areas: mean area = [A1*A2]^0.5 for simming purposes. That said, Hornresp can do accurate enough sims just inputting the two areas and length as well as the horn flare.

Thank you for the suggestion and link to Hornresp. I know horn design is in my future, but didn't know the time was now. I have not used this slick software before. I'll pull up the help file, and see if I can find the fields you suggested I simply input to see how these ports add up...

Any pictures?

Attachment 4371

Blast from the past. Carvin actually offered the 421 in that enclosure.

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Originally Posted by Old Guy

Blast from the past. Carvin actually offered the 421 in that enclosure.

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Incredible the stuff you remember right off the cuff, OG.

;)

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Originally Posted by Alien_Shore

Incredible the stuff you remember right off the cuff, OG.

;)

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Carvin offered Altec as their premium option. I used some of their gear as a teenager.

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Originally Posted by Old Guy

Blast from the past. Carvin actually offered the 421 in that enclosure.

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Interesting! Vents way larger than the driver's piston area without proper horn loading is normally a recipe for disaster unless there's a near infinite slope limiter.

Wow, OG, thanks. This is really good news, that 421-8H may be a good match, and not require much modification. I plan on measuring the enclosure and ports, and posting a sketch to hope for some guidance on any mods. Thanks again to all!!

I'd like to find or make some handles for the openings on each side, and need terminal cups. The handle openings are 5 1/2" wide, and the abundant metal handles I see for sale are for 4.5" wide openings.... Fitting 3/4" plywood infill pieces is all I can think of to make new ones work, or just cover the openings from the inside with 1/2" ply. Suggestions on that and how much acoustic batting to try initially are more than welcome to this newbie. :)

Check Parts Express for handles

Large Steel Bar Speaker Cabinet Handle


https://www.parts-express.com/tools-supplies/hardware/handles

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Originally Posted by GM

Interesting! Vents way larger than the driver's piston area without proper horn loading is normally a recipe for disaster unless there's a near infinite slope limiter.

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Yes port is way too big