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Old 25th November 2005, 06:10 PM   #21
sasha is offline sasha  Canada
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Hi Brian,
Your project sounds exciting, and I hope You will persist and finish it.
If I understand correctly Your cylinder will consist of multiple flat panels
right? I have an idea for taming inside sound waves and preventing
the inside sound to escape. Of course, damping material is necessary.
I think with this "star" inside the cylinder it would be impossible for opposite panels to acoustically "see" each other.
And star will be far enough from panels so they can "breath" easy.
Regards.
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Old 25th November 2005, 06:43 PM   #22
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Basukaz,
How did you construct your cylinder? Mine are flat facets (16) around a circular cross section, much taller than wide. Each facet is a normal element with diaphragm tension in two dimensions.

Sasha,
The movement of the inner compression/rarefaction wave is toward the center point like a collapsing circle. A star as you propose is in line with wave particle motion and therefore does not present any boundary effect (if the star walls are very thin.) This is symmetry at play. Similarly, you could build a pie-shaped piece of the cylinder with fewer facets and fixed inner walls in a closed wedge shape (which I have done) and if you combined several of these wedge segments into a full circle, this represents the same environment to each facet as an open interior. Hard to believe perhaps, but true. There's a lot of wavefront combining and cancelling within the open interior which is counter-intuitive. You have to keep symmetry by your side as an ally. Wave behavior can be tough to grasp unless you've done work in acoustics, optics or antennas.
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Old 25th November 2005, 07:31 PM   #23
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Default internal cylinder damping?

Brian: this is all very interesting and I would like to hear more about your ideas on damping the panels back wave inside of the cylinder. I do wonder about how to deal with compression of the air inside of such a sealed system. I should have thought that fiborus damping alone would not be enough to disapate the pressure buildup inside of the cylinder. This must result in diaphragm motion unless the structure is very large. I guess that I have to keep in mind the small travel of the ESL diaphragm. Your comments would be of interest in this respect. Thanks Best regards Moray James.
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Old 25th November 2005, 09:42 PM   #24
Bazukaz is offline Bazukaz  Lithuania
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I rolled it from fine wire fence , with some round rings inside to make it stronger.

Also i have found that cooking bags are very fin and have the properties very similar to Mylar.They are strong , scuffle and
shrink when heated well.

Maybe it is Mylar ?
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Old 26th November 2005, 05:02 AM   #25
el`Ol is offline el`Ol  Germany
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Quote:
Originally posted by Bazukaz
I have just built a little round cylinder (~5 x 25 cm) , but there are seriuos problems with diapragm tension.

If one would pull ladies` nylons over the cylinder and use latex milk with graphite powder to seal them, would that be too heavy -
or too non-linear in tension?
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Old 26th November 2005, 11:49 AM   #26
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Quote:
Originally posted by Bazukaz
I rolled it from fine wire fence , with some round rings inside to make it stronger.

Also i have found that cooking bags are very fin and have the properties very similar to Mylar.They are strong , scuffle and
shrink when heated well.

Maybe it is Mylar ?

Cooking bags, they come in differnt lengths, widths.
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Old 26th November 2005, 02:27 PM   #27
el`Ol is offline el`Ol  Germany
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I can imagine that the tension of shrinked mylar is probably too high for a cylindrical cage with distance of the bars of just a few centimeters.
What is the opinion of the experts?
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Old 26th November 2005, 06:27 PM   #28
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Default Ted Jordan's Membrane Absorber

Brian: years ago Ted Jordan published a series of articles on speakers and in one of them was a design for what he called a membrane absorber. This wad comprised of a raised frame of wood strapping with a solid back. The inside of the framed off area was then filed with fiborus material and then covered with a thin plastic film. The fiber had to make firm cintact with the film. Shrinking the film insured that the contact was good. The whole structure needed to be air tight to work. As a closed system a pressure wave would press against the film which in turn compressed the fiber which would spring bacl against the film. This process would then continue untill the energy was disapated. These absorbers work very well. A version of this could be made in a long clyndrical form and run vertically from top to bottom inside a cylndrical cabinet with ESL panels surrounding it. As with Ted's design it would need to be a closed air tight system. These absorbers are very efficient in disapating energy.
Thought I would remind you about this idea incase you think that it might be helpful in your design. Best regards Moray James. PS these work extreemly well to line the walls of transmission lines. They eat a lot of energy while not restricting any air flow in the line and so help keep efficiency of the line resonance high.
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Old 27th November 2005, 01:30 PM   #29
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Thanks Moray. I hadn't read Ted Jordan's works. My approach is more down the path of anechoic chamber wedges and the possible use of Helmholtz/Hegeman absorbers for the longer wavelengths, but I have much work to do before claiming any success. Do you have copies of Jordan's work, a reference, or a link? Take a look at Roger West's SALLIE, a backwave attenuator for his open dipoles. This isn't quite what I had in mind for the interior of a cylinder, but it gives an idea of an alternate approach.

http://www.soundlab-speakers.com/accessories.htm
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Old 27th November 2005, 05:41 PM   #30
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Default Thanks Brian

Brian: will have to have a look and see if I can find the articles to get you a reference. I think that they were first published in Wireless World in the 70's but I cant be sure of the date. Thanks for the info on the Sallies. Regards Moray James.
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