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Hello ,
I recently purchased some 817A replicas built by pbn audio. They are very heavy, ~350 lb ea and very well braced. I am extremly happy with them ..except they seem a little over damped. The internal stuffing is acoustic egg shell foam covering entire surface of interior cabinet. Thoughts on what others have use in these horns??
I pulled a small amount of the foam out the other day and noticed an slight improvement.. more open was thinking about using some 2" cotton batting instead of the foam and not covering entire interior..
Thoughts?
Thnks
Keith
Follow Ups:
It's not really an apple to apple comparison since my cabs are full horn, and not reflex / horn but a few years ago I managed to completely over damp my Peavey FH1, to the point that their output was greatly reduced. I had covered all internal walls of the rear chamber (the "doghouse" as Klipsch people say) with bitumen sheets and covered those with eggs crate foam of high quality. Well, I removed almost all the foam, leaving it only on one of the two horizontal panels, since there are no other parallel walls, and that did the trick. Better than the undamped horn, but still alive!
Depending on the enclosure more or less damping is needed. It's a little bit of trial and error until you like the results!
Fully lining the cab is standard procedure. Any internal reflections back to the cone will cause peaks and valleys in the response, although you may prefer the sound with said peaks and valleys.
Yes, I'll have to experiment. Do you have any thoughts on the foam vs mineral wool or cotton bats?.
Thanks
Keith
Foam is the least effective, being of the lowest density. Also note that pyramid foam consists of air in between the peaks, so it's effective thickness is much less than it appears to be. Then comes cotton, then mineral wool.
Altec used fiberglass back then. Maybe the most authentic if that matters to you.
Fiberglass, specifically Type 700 rigid boards, is the most effective damping material. Fiberglass insulation should not be used, as it falls apart.
this stuff?
Open up your mind, in pours the trash. - Meat Puppets, 1987
It has a heavy layer that doesn't do anything for a well constructed cabinet. The foam layer is OK, but no better than any other brand of foam. If it didn't cost four times what other materials do I'd say sure, but it does. I use heavy vinyl mastic in my car, where it's the only way you can control panel resonance.
On the subject of price, foams sold as acoustic foam cost considerably more than furniture upholstery open cell urethane foam that works just as well. You can get that at Walmart and at fabric stores, like Joann's.
nt
Open up your mind, in pours the trash. - Meat Puppets, 1987
I get the stuff made to insulate ductwork. Its not the paper backed stuff used for insulation between studs. It comes in a roll, and keeps its shape quite well.
I staple using 6" spacing never an issue. I've seen cheese cloth used on top though. Roxul is a good brand of rock wool, fairly dense and 2-3" thick panels.
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