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.
I tried to do a google image search, but nothing appeared, maybe Romy will share.