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Old 2nd November 2012, 08:32 PM   #28841
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Originally Posted by jneutron View Post
It's like fiber cables.
With a little difference considering the wave length of the light VS the diameter of the fiber ?
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Old 2nd November 2012, 08:37 PM   #28842
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Originally Posted by Esperado View Post
With a little difference considering the wave length of the light and the diameter of the fiber.
The ratio is quite different of course. My fiber analogy was more a single mode/multi mode/path length thing.

But actual measurement of the effect in a horn is a tough nut.

I can see how listening tests would be the primary test method.

I must admit confusion as to the foam thing explanation, as I'd expect a "percentage of whole" being absorbed, not 10 out of 20 vs 10 out of 100.

Perhaps Mr. G can elaborate on why?

jn
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Old 2nd November 2012, 09:02 PM   #28843
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I can see how listening tests would be the primary test method.
About listening tests, comparing with spherical waves calculated horns.. hum... how to say ?
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Old 2nd November 2012, 09:29 PM   #28844
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Originally Posted by jneutron View Post
Perhaps Mr. G can elaborate on why?

jn
I have been and will be rather sketchy on all of this here because its not the appropriate forum for the discussion of waveguides. This has been discussed at some length over in loudspeakers.

You are quite correct about the modes in fiber optic cables. Its very analogous, except that in waveguides the walls are not parallel and hence the modes are not only much more complex, but they change as they propagate. Fiber modes don't do that.

You are also quite correct about the difficulty in measuring the HOM. This is why when I hear that someone has done it, I am very sceptical. It was done, once, by a guy at Aachen using a microflown and a scanning device. He measured their presence but nothing else. His setup would be impossible in a setting like I have.

By "proof" I meant that my devices have been in the marketplace for more than a decade and they work in practice just like the theory says that they should - the main parts, not the HOM. The HOM are pretty hypothetical at this point - except that their existance has been proven in theory and in measurements, but their audiblity is a work in progress. Given that all the testable parts of Waveguide Theory have proven to be correct, I have every reason to believe that the HOM claims will also be shown to be correct when such measurements are feasible.

Regarding the foam, I am not sure if it is a percentage or a flat reduction. In either case my point is that with a device with high HOM the foam is not very effective, but with a low HOM it is. Although I have heard people say that it works well even on bad devices - could be. Its the claim that I use foam because the HOMs are large that is completely bogus.

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Old 2nd November 2012, 09:39 PM   #28845
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If the metaphore (multimode fiber) actually holds then the HOM should be evident from dispersion in a short pulse, as it is in fiber optics.
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Old 2nd November 2012, 09:46 PM   #28846
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What if to observe some smoke inside of the waveguide?
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Old 2nd November 2012, 10:41 PM   #28847
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Originally Posted by Wavebourn View Post
What if to observe some smoke inside of the waveguide?
And what about simulations ? (fluid dynamic)
(btw: JMLC 's community has provided very useful sim tools, they improve them continuously, they correlate more and more with measurement and they show with evidences the diffractions problems induced by any lack of progressivity near the throat.)

On my little experience, dumping horn with different foams, glass wool etc.., i had good results with bad horns or waveguides on the response curve, while terrific deterioration with good horns. ( loss of efficiency, added distance the sound source, and loss of intelligibility or definition not related with the obvious loss of trebles ).
May-be Mr Gedlee can explain that ?
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Old 2nd November 2012, 11:36 PM   #28848
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I use YOUR designs in MY test equipment as well. Just not for audio playback.
About two hours after that post someone walked into my office with a package from the CEO of Stanford Instruments that he had lost for over 5yr. It was about all of my stuff he uses. Scarey.
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Old 2nd November 2012, 11:41 PM   #28849
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Damping adds distortions. It is non-linear. You trade-off frequency response for distortions. No free cheese for mice, except in the mousetrap!

Let me google that for you
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Old 2nd November 2012, 11:42 PM   #28850
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About two hours after that post someone walked into my office with a package from the CEO of Stanford Instruments that he had lost for over 5yr. It was about all of my stuff he uses. Scarey.
Now wait for me with optical microphone array. It is even scarier.
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