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In the Forum: Horn-Loaded Speakers
In the Thread: Jessie Dazzle Project
Post Subject: Orientation of fibersPosted by jessie.dazzle on: 7/26/2008
Klaus wrote :
"...maybe i'm wrong, but as far as i see it, the whole thing has to be stiff on the outside. will make the horn in a way to survive a "explosion" on the throat, the pressure will try to expand the horn to the outside, so it should make sense to use unidirectional inlays on the outside. inlays are much cheaper than fabric and stronger in one direction..."
Yes. It ain't exactly the same, but imagine you had a bunch of rope, and wanted to reinforce a log, making it more resistant to the forces of a wedge being driven up it's central axis. Think how you might reinforce a can of beer (to resist internal pressure) using only a spool of string. Look at rocket motors (big ones)... They are filament-wound, wrapped in layers alternating by what looks to be around a 60° included angle.
You are correct to look at the problem from the point of view of beam strength (your example of standing on a board). The wall of the horn can be compared to a beam if you imagine holding a composite sandwich section of the horn (a test horn that you cut up). Now imagine how you want to make that "beam" more resistant to bending. The effective means of doing this is via an increase in the area closest to what's called the neutral axis of the beam, or the center running along the beam's length. The closer the material is to this location, the more it servers mainly as a spacer, which must resist radial loading (think of the beam bent into a curve... forces of compression and tension would radiate perpendicular to the beam's major axis)... The job of material closest to the neutral axis is to insure that the out side surfaces of the composite are held at a constant distance relative to each other. These outside surfaces however should be resistant to axial loading (compression and tension along the length of the beam).
If you orient the fibers only inline with the firing axis of the horn, you will in effect be adopting a constructing that would make the whole of the horn resistant to bending in the same way a tree resists bending. Your horn is not going to be subjected to wind... Something for which trees were designed to resist... The load your horn is likely to receive is more akin to a log receiving a wedge inline with its major axis. The result is of course an easy split.
So... If using only one layer of unidirectional, orient the fibers such that they wrap around the horn at 90° to its firing axis. Ideally (if you're rich), unidirectional laminations could be alternated (2 at 90° to each other, or 3 at 45° to each other)... In this case you might just as well get the woven stuff.
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