GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Horn-Loaded Speakers
In the Thread: Macondo’s Midbass Project – the grown up time.

Post Subject: From Maquette to Full ScalePosted by Paul S on: 7/29/2010

Romy, is it a goal to make the horn strong enough to raise one end or turn it without having it fall apart from its own weight?

From your earlier descriptions, I expected to see at least one continuous piece of plywood bridging the full length of the horn, to tie it all together. I also expected to see glue blocks, perhaps some temporary clamping blocks (to facilitate clamps that pull sections together until the glue dries, maybe some band clamps, continuous cleats rather than small temps or small permanent cleats that will interfere with continuous braces/cleats in the future, if that is still planned. At least, I would expect to see "biscuits" where edges are joined, both edge-to-edge and L joints, to get and keep everything located/lined up and to strengthen those joints.

Another trick I do not see is any sort of control templates, to ensure that sections destined to mate together will do so directly, since you likely will not be able to "rack" the glued-up sections together once the glue has set. Any diviation in any plane makes for big fights trying to line up and effectively glue thick plywood sections like these. Maybe as a hedge you could glue up each section while it is lined up temporarily with its ultimate partner/partners, to ensure subsequent compatibility.

The weakest parts of this horn will likely be the full edge-to-edge joints between the pre-built sections. IMO these warrant the "braces" you spoke of earlier, and, again, they shoud be installed as part of the skin, then glued, clamped and screwed together along the edges rather than added as afterthoughts.

Because of the frequent changes in the "cord" of the horn it will be a challenge to come up with continuous "braces" or cleats to cleanly bridge all the "natural", directional breaks in the horn. But IMO this is something that should be undertaken sooner rather than later. One idea is to make the "braces" themselves out of plywood, so they'd combine the functions of braces and cleats and still function as part of the horn shell, as well. Also, maybe, some "bent" cleats could be fashioned from framing hardware and fastend with short, self-tapping "truss head" screws at the "bent" joints. Just understand that any cleats are a supplement to rather than a replacement for well-fitted, glued (and clamped) joints.

Best regards,
Paul S

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