My A7-500s. A journey

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Originally Posted by Audio_by_Goodwill

You won't hurt anything by pouring something in like sand. The only force would be the weight. You do have to be careful if using expanding foam. It the foam expands to much it will start cracking the wood.

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The foam will follow the path of least resistance, were I foaming a sealed area I would drill vent holes. Not 1/4 inch ones...one inch or so...

That's a pretty good idea!

My horn flares do still vibrate, but less than the sides and back, so progress has been made. They were soooo bad to begin with. The bracing and damping really cleaned things up.

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Originally Posted by Panomaniac

Yes- really bad not to have the braces. They are definitely needed. In fact 2 per side should be the norm. And funny that my boxes used smooth ply for the flares. Not kerf cut on the back, like most. So maybe thinner than most. Tho the plywood on the boxes is decent and 3/4".

Yes AB, the flare that was loose vibrated the most. But they all resonated.

There is a set of big double 15 JBL horn cabs here in town that I know. Awful construction! Thin, resonant, flimsy. So it was not just Altec. Just Big and Loud was also Just Thin and Cheap. :p

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I guess a bunch of glue blocks and such are in order :(

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Originally Posted by Audio_by_Goodwill

You won't hurt anything by pouring something in like sand. The only force would be the weight. You do have to be careful if using expanding foam. It the foam expands to much it will start cracking the wood.

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I don't think you would want to pour sand in there that would be quite abit and if you ever have to move them you will be drilling holes in the side for the sand to pour out.:o If you use expanding foam you have to get the stuff for Windows & Doors it doesn't bow the wood it just fills the gaps without putting unwanted heavy pressure on the wood :)

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Originally Posted by Altec Best

I don't think you would want to pour sand in there that would be quite abit and if you ever have to move them you will be drilling holes in the side for the sand to pour out.:o If you use expanding foam you have to get the stuff for Windows & Doors it doesn't bow the wood it just fills the gaps without putting unwanted heavy pressure on the wood :)

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They're quite heavy to move any way. I don't see it making much difference once a dolly is used.

As far as the foam goes, the Window and Door stuff just means that you'll end up buying more, since it doesn't expand as much. I like OldGuy's idea of drilling vent holes in the rear so it's not totally trapped. I'd also likely do it in stages......waiting for the first run to stop expanding before topping it off. Since I don't have 825/828's anymore, it's not something I'll be doing anytime soon.

The vent hole/expanding foam idea sure sounds like it should work, but I can say from experience it doesn't, at least not like one would expect. I filled from the bottom panel, front, with 2 3/4" vents at the top of the (rear) baffle (with the boxes laying face down so it would fill "up"). If I hadn't had several 2" rachet straps handy when things started popping and cracking, I'm confident the foam would have blown the flares right out of the boxes. As it turned out, the foam exerts a lot of pressure against the flares, and any remaining resonances appear to be out of the pass band.

IIRC, I just used 1 can "Great Stuff" per flare, which was too much from one POV and just right from another. Mine had a little less volume to fill than stock, as I laid on an inch of wire-reinforced concrete on the back of each flare first.

While mine ended up great, if I were to do it again I'd spend the extra $ on 2-part foam with predictable expansion.

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Originally Posted by Panomaniac

I don't know what folks with the sealed off cabs can do.........No way to get in there and brace it. Maybe pour in sand or kitty litter, as GM suggests.

The back panel resonates, too.

Just Big and Loud was also Just Thin and Cheap. :p

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Note that completely filling the voids with a relatively massive material is theoretically infinitely bracing it, the main reason for my recommendation. ;)

Right, as a rule-of-thumb for high SQ plywood speaker construction you want to either break up large panels until they are a collection of ~ 1 ft square areas or better still, broken up into different area triangles. Note that while it's contrary to the popular 'window' style bracing, the brace in theory shouldn't extend (tie into) the corners or to other braces, but only be ~71% of the span to keep from creating or increasing the intensity of any 'hot spots'.

For the tower designs I prefer (TL, MLTL), i.e. any high aspect ratio panel, vertical braces offset at a golden (1.0-1.618) or acoustic ratio (1.0-1.14, -1.17, -1.25, -1.28, -1.39, -1.41, -1.45, -1.47, etc.) work well. Note that the high pressure point in these designs is at the closed end, so ideally you want to mass load the top plate, though in a bifold design the 'top' is on the bottom, so not required if placed hard against a rigid/massive boundary such as a floor.

True, but these type of cab's S/N ratio fall well below a typical human's ~ -25 dB threshold for the cinema/prosound apps they were designed for, so a waste of $$$ for these smaller units.

GM

Good stuff GM, thank you! :)

I always went by the "middle wiggle" ROT; brace the central ~3/4s of a span to double the primary resonance F. Thirds is probably better. If that dosn't "get you there", do it again some more... ;)

You're welcome!

GM

Having some weight toward the front of the box would not be a bad thing. With the magnet of the 15" near the back, and that giant 291 hanging behind the back, it all starts to get a bit tippy.

I might toss a sandbag in the front of each.

Things are sounding very nice now. Just need to get the tweeters right....