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In the Forum: Horn-Loaded Speakers
In the Thread: Macondo’s Midbass Project – the grown up time.
Post Subject: The Solution.Posted by Romy the Cat on: 7/22/2010
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 Romy the Cat wrote:

Last night I was playing with my ¾” Baltic Birch. What I realized is that my Jew frugality played a bad joke on me.  At this point I do feel that ¾” of plywood is not enough thickness for my 43.5Hz horn. I understand that it will be heavily braced, perhaps each 8 inch but still I do not like it p I would like more substance in the horn skin. If course not only the Jew frugality and my desire to buy less plywood made me to decide for ¾ inch. The weight was a big consideration factor and the fact that 1.5inch wall for instance will minimize the operational, useful volume of my horn’s mouth. Anyhow, now after hours of dealing with ¾” Baltic Birch I do feel that it was a mistake – I need a thicker walls.

Now is the question what can I do? This is complicated as the math for the ¾” is doe and we are pretty much ready to cut the wood. If I glue two of ¾ layers then it will be twice heavier, still I wonder if it makes sense for me to go for it. I have some alternatives that I am weighing now.

1)      Each section between the brace to feel with mixture of send and roofing contrite.  The roofing contrite is tar-like plastic that is wonderful dampening. I might even drop into the roofing contrite some lead shots (I have 800 pounds)

2)      To make colossal amount of bracing, pretty much to built a second layer with 2 x4 that will sit behind the plywood on screws and polyurethane glue.

3)      Discover if exists some kind of heavy-mass construction spray-adhesive (foam) and to damp that foam (perhaps mixing it with sand) into the section between the 2x4

4)      Forget the frugality and reasoning and to glue second layer of plywood to my current 3/4 plywood

I have all options on the table now…


After much consideration I think I came up with a solution of the horn skin problem. I will do the recursive variable thickens. The horn will have 7 chords. He even chords will be made by 2 glued ¾ layers with 2x2 braces.  The uneven chords will be made by one ¾ layer and 2x4 braces and the 1” mix of sand, led shots and roofing cement purred into the sells between braces. The order of even and uneven surfaced will be different for vertical and horizontal sides. Considering that each chord has its own length the pressure wave in horn will not see any systemic alternation of mass and it will be more or less random. I think this solution would be an OK compromise between overbuilt solidity and economics. In fact, since roofing cement and double-layer have different damming characteristics I presume that my way of making the horn might be even superior is to a solution of making the whole horn from 1.5 inch continue-thinness of wood. Since I did not see anybody did this way I would grand to this solution my own name – thy “Chess Skin”. The image below well depicts the idea. The Red sections are double wood 1.5” and the blue are roofing cement with sand and led. I might even go for super-mixing and make ERACH two neighboring sells with red or blue construction. It will even more randomize the structural integrity of the horn.

Midbass_progress_19.jpg

Are to planing to stop by in a few weeks to lift the thing 20 feet upin air before we slide it to the attic?

The Cat

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