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Old 31st December 2019, 02:04 PM   #741
mabat is offline mabat  Czech Republic
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This was not about absorptive walls but about edges on a hard wall. So how will edges on otherwise hard and reflective surface help for better guidance? I did some experiments with added wall "edginess" in simulations but it was never any better than a smooth surface so I would just like to see some counterexample.
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Old 31st December 2019, 02:12 PM   #742
Ro808 is offline Ro808  Netherlands
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Did you ever compare 2 identical waveguides, one with a smooth, glossy finish and one with a Nextel coating?

I can tell from experience the first speaker sounds considerably better than the scond one.
But that's still no hard evidence based on data, of course.
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Old 31st December 2019, 02:14 PM   #743
mabat is offline mabat  Czech Republic
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No, and please, show me such data.
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Old 31st December 2019, 03:13 PM   #744
Ro808 is offline Ro808  Netherlands
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"Our cabinets are now coated with the patented material known as Nextel©. It's a matte textured coating that absorbs light and sound. It reduces cabinet diffraction effects and absorbs surface vibrations for a more silent cabinet."

There's a lot of research available wrt Nextel by NASA ea. Admittedly, it's primarily focussed on reflection and absorbtion of light/heat.

Quote from another forum:

"christensenleif said:
another conclusion I´ve come to, is that a Nextel coated horn sounds smoother than a glossy piano finish
getting associations to the dimples in golf balls
mentioned this to Rune Skramstad, Bjørn Kolbræks doctorate tutor, and they wanted to calculate on it.......
beyond my math level....o_O
actually one of the other guys who got the alu 2500 for the 2002 had it painted in Nextel
would be cool to compare....
Maybe it helps to minimize the high order modes (HOMs) that led Earl Geddes to put foam plugs in his oblate spheroid horn/waveguides?


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Sound Castles klg
Swiss Importer/distributor for Aries Cerat Ltd."


Though I prefer not to, I'm willing to accept some acoustic phenomena are very hard to quantify of not (yet) measurable.

Last edited by Ro808; 31st December 2019 at 03:38 PM.
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Old 31st December 2019, 04:04 PM   #745
mabat is offline mabat  Czech Republic
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It seems I don't share this appetite for miracles.

Anyway, my original doubt was whether these edges, given by print in a coarse mesh, are actually good for anything. I'd be surprised if they did.
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Old 31st December 2019, 04:10 PM   #746
Ro808 is offline Ro808  Netherlands
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Miracles will happen

I doubt the coarseness of that particular mess will do any good.
Medium grid sandpaper seems to work though.
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Old 31st December 2019, 04:14 PM   #747
turk 182 is offline turk 182  Canada
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Originally Posted by moray james View Post
isn't the inside surface tension of the wave guide or horn a matter of weather or not you want to generate drag (friction due to turbulence/resistance) on the outside edge of the wavefront as it leaves the mouth? for example a smooth surface will help to keep the exiting wavefront flat while a rough surface will result in adding some drag to the outside edges of the wavefront making for some curvature all be it a very small amount?

while a rough surface will result in adding some drag to the outside edges of the wavefront making for some curvature all be it a very small amount?


i've extracted this portion of your statement as i feel this is a salient point!


could this not give rise to a means to control the off axis response?


to wit diffraction is not per se evil and can be used to good effect if controlled/tailored to achieve a specific result, no?
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Old 2nd January 2020, 04:22 PM   #748
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Hi, Mabat. Thank you so much for sharing your excellent work. Being much less mathematical myself, i was wondering if you could help me out with one of your equations.
Im sketching in Inventor, using the equation curve tool. Is it possible to arrange an equation with the mouth dimension as an input and the depth as a free variable?
Too me, the most significant difference between the clotoid/super-ellipse seems to be the user friendliness and perhaps the greater flexibility of the SE-equation, so whatever is the simplest to work with is preferred.
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Old 2nd January 2020, 07:34 PM   #749
mabat is offline mabat  Czech Republic
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The math gets ugly very quickly, but if you want to start with some mouth size and determine the length from that, try this -
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Old 2nd January 2020, 09:22 PM   #750
454Casull is offline 454Casull  Canada
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The math gets ugly very quickly
You weren't kidding.
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