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Posted by Romy the Cat on
12-28-2015
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fiogf49gjkf0d Speaking about the interesting surface finish. I have seen a
new stimulating idea that I call the Scratched Horn. I do not know how much
practical effect if has but it shall not be bad. Let pretend that it is not a conical
horn with even sides but Tratrix and the scratching channels slowly spiral from
the trout and then become to spiral very aggressively at the horn mouth. So, the twisting of the scratches would be proportional
to the curvature of the horn. That would be a hell of a work to do but it would
be very interesting to hear and compare with a conventional horn.
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Posted by Gargoyle on
12-28-2015
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fiogf49gjkf0d Two things I see with that horn. The ribs will have an effect on dispersing internal reflections, positively I'm assuming.
The second thing, the ribs are causing a fairly substantial increase in surface area inside the cone, it has the surface area of a larger horn.
How this affects the sound I can only speculate.
I guess it depends if you want the air to stick to the cone or enhance it's release.
That cone reminds me of the business end of a Saturn V rocket. It is lined with little tubes that circulate fuel to cool the engine. Probably oriented in the optimum direction.
It also reminds me of that episode of Mythbusters in which they covered a car with clay and cut scallops in it so that the surface resembled that of a golf ball.
Sure enough, the dimpled car was better on fuel (less drag) then the same car without all the heavy clay and dimples.
I have a really old horn here that has a textured finish. One can assume in that era that a lot of things were done empirically. They had the ability to go smooth, but didn't.
Maybe the effects could be modeled with smoke.
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Posted by noviygera on
12-28-2015
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fiogf49gjkf0d Ask the makers if that horn? Maybe they have something to share about it.
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Posted by Gargoyle on
12-30-2015
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fiogf49gjkf0d I tried to do a google image search, but nothing appeared, maybe Romy will share.
I got to pondering what benefit having the surface textured may have. It seems the texture of sharkskin for example can reduce the surface suction.
From the interweb:
"A silicone-replica of the skin of the copper shark Carcharhinus brachyurus attached to a rigid flat plate resulted in a drag reduction of 5.2–8.3% compared with that of smooth silicone on a flat plate (Han et al., 2008)"
"A hard plastic shark skin replica achieved a drag reduction of 3% (Bechert et al., 1985). But these cases involved study of a rigid body covered with a biomimetic skin, which is not the situation for a shark in vivo,
where body undulations can greatly alter the structure of surface
ornamentation and change flow characteristics over the skin"
From the quotes above it seems in the case of the shark skin, it needs to be somewhat soft as well as having a certain coarse texture. A drag reduction of 5%-8% is substantial.
I was also somewhat intrigued by the near silent flight that an owl can achieve and what could be borrowed from that technology. Sharp little ribblets on the leading edge of the wing serve to chop larger vortices into smaller ones, as well as having soft feathers on the trailing edge that serve a similar purpose in decoupling the owl's energy from the air around it.
I was watching an interesting video with HornResp, now I know you guys may or may not care for it, but it does have an interesting animation relevant to this discussion. (I would also like your critique on the 200Hz horn being modeled, perhaps I can shoe-horn that into this discussion as it will be relevant for my experiments.)
So this animation shows what we would typically expect, a curved convex wavefront. Now this may or may not be intrinsically necessary to amplification, but one has to wonder if there was reduced suction at the surface of the horn, would we yield a flatter wavefront?
It is also interesting to see what happens to the energy when the horn reaches it's lower cut-off, you can see it wrap-around and get stuck behind the horns mouth.
It looks analogous to a liquid leaving some sort of dropper. With some experimentation with both the horn's internal surface and the mouth's edge of the horn, perhaps low frequency performance could be enhanced if the suction was reduced at those regions, say with fuzzy owl feathers for example. 
Apparently I am an idiot, so you will have to copy and paste the link to the video.
https://www.youtube.com/watch?v=ecVXEFb0mXY
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Posted by noviygera on
12-30-2015
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fiogf49gjkf0d Maybe lining the horn interior with rough cork or something would achieve the same function like this horn
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Posted by Gargoyle on
12-31-2015
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fiogf49gjkf0d Yes, although the typical cork sheets might be too smooth and hard to apply. However if you were to crush the cork into granules... then apply to the horn, that should be feasible.
Can you tell us anything about the picture you just posted? It doesn't show up on a search either.
(I will put your cork suggestion to the test in another application. I was pondering some kind of rubber-like additive to add to the paper mache experiments. Cork should be a great alternative to rubber, for many reasons. )
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Posted by noviygera on
01-05-2016
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fiogf49gjkf0d nt
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Posted by rowuk on
01-07-2016
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fiogf49gjkf0d Audio is a AC event not DC. There is no wind blowing except for poorly designed ports. There is no reason to "optimize" for lowest "drag". The air molecules bump into one another and really do not travel any distance. There are claims of better sound with a slightly "rougher surface" although no one can explain why. Romy has on several occasions expressed a difference when the horn is highly polished. Maybe the secret has something to do with minor diffraction or a specific randomness at the edges of the soundwave?
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