Superconducting Voice coils (Split from Fast Bass)

[BassAwdyO]

John,

Do you know much about the meissner effect? I have this idea that it might be possible to use it to help concentrate the magnetic feilds and keep those bad things from happening when the flux gets up past a few tesla.

[jneutron]

Originally posted by BassAwdyO
John,

Thanks for all the info... A bit of it is beyond my knowledge of superconductors. Maybe you should be designing the world's first Superconductive loudspeaker instead of me!

Where did you find that stuff? I've had a hard time finding any technical information about HTS wire anywhere. I would like to research it thoroughly myself.

Um, it's what I do for a living..

Here's a link to the stuff on the HTS wire..

http://www.amsuper.com/products/htsW...3419093341.cfm

Typically, the wire vendors will not provide much in the way of detail when it comes to using their product. For complete cable solutions as an example, they will sell you a full 3 phase tenth of a million volt 20 or 30 kiloampere wire run, but won't teach you how to make one using their product. The construction tidbits I gave are just from experience..

Designing a superconducting speaker is quite trivial, as typical applications I deal with run 10 to 15 KPSI lorentz forces...the biggest problems will be mag field safety,ODH issues, and frostbite.. That, and the liquid useage will be very high for such a small power application as to be useless..even at 32 cents a quart, it'll take a lot of LN₂ to keep it cold. Overall, a superconducting speaker can be very difficult, and can be dangerous ta boot..

Cheers, John

[jneutron]

Originally posted by BassAwdyO
John,

Do you know much about the meissner effect? I have this idea that it might be possible to use it to help concentrate the magnetic feilds and keep those bad things from happening when the flux gets up past a few tesla.

In theory, doable..I've proposed it several times here for magnets that have to drop field intensity very rapidly, but it always seems to get quashed for some practical reason...go figure...those silly physicists...

Cheers, John

[jneutron]

To keep the design reasonable, you have to separate the motor from the cone. If you use a tubular connection rod made of kevlar or composite graphite, you can have the motor as a seperate entity.

To insulate the cryo sections, you'll need to either maintain a thermal gradient with nitrogen boiloff, or use a vacuum..

A vacuum is a problem for the connection rod..motional seals will have to be very flexible, and you need two, one on each end, to eliminate the 15 psi resulting. If you assume an xmax of an inch or two (hey, might as well make use of the materials), that makes the seals an issue for vacuum..normal seals are stainless bellows, they'd fatigue way too fast..

If you use the nitrogen boiloff, the seals could be simple thick felt sliders...you could try o-rings, but they'd have to be something that remains flexible down near 77K. The coupling rod will conduct heat inward, so you'd be fighting the ice ball at the seals. A thin styrofoam insulating layer over the rods would help. On the inside of the cryo system, graphite axial fins would help keep the rod cool near the supers..I'd go with designing the rod with taper and incorporate the vc in the structure..you can buy graphite unidirectional weaves online...I'd use west system's epoxy with the tropical hardener for pot life..

Connections off the rod would have to be normal material, as the hts will not survive the flexure. Bond the hts to the rods soldered to copper flat stock for at least 2 inches overlap...then, copper litz off the rod to the stationary connection. One on each side of the active voice coil, that way, you do not have to worry about the layer transition area required for a two layer vc with leads out one end.


The field coil is trivial in comparison.

Cheers, John

[BassAwdyO]

well the ultimate superconducting speaker would have a superconducting voicecoil and a superconducting magnet and maybe some feedback loops in there too but if we cant really do that, then might as well just do a low inductanc feild coil superconductor with a long high inductance voice coil which would be fed a constant voltage. the superconductive feild coil could do all the changing... any problems with that?

[jneutron]

Originally posted by BassAwdyO
well the ultimate superconducting speaker would have a superconducting voicecoil and a superconducting magnet and maybe some feedback loops in there too but if we cant really do that, then might as well just do a low inductanc feild coil superconductor with a long high inductance voice coil which would be fed a constant voltage. the superconductive feild coil could do all the changing... any problems with that?

Um, yah...sorry...

Eddy currents within a conductor are dependent on the rate of change of the magnetic field trying to go through.

A superconducting voice coil will force the magnetic circuit to change it's total flux, and the gap field will be perpendicular to the voicecoil winds..meaning, as you increase power or frequency of the drive signal, you will start to heat the HTS tape. Start to leave the gap, and poof, you're up about 100 degrees.

AT 77K, all materials have reduced heat capacity...Helium is the lone exception. Copper vc would work also, as at 77K, it's heat capacity is .17 Joules/gram-K, vs room value of .38...half.

And, it's resistivity is about .1 e^-8 ohm meter at 77K vs room value of 1.7. You pick up a 17 to 1 advantage just by cooling it..

Cheers, John

[CBFryman]

a lot of this is out of my knowldge an a lot i can also understand...but damn im only in HS

But from my understanding i think that pulling this off will be a VERY large task. and that is just to get one fo actually play some sort of tone. getting one to work like todays drivers work...well its going to take years and years of development. you may get one right by the time you are too old to care.

Someone suggested a lump of superconductor in place of a magnetic feild. however you are having to buy 200 meters of superconducting wire.

an idea. put a coil inside a coil. with opposite polarities. wire them in parallel out of phase so they will be repeling then atracting each other. i have no idea if this would actually work or not but its an idea i am thowing out.

another idea is to have a driver that works 1 way. indstead of the back and forth movement. Because superconductors repel magnetic feilds you could have the coil inside a coil idea, and only play half the sinewave and the other coil un powered. then rely on the suspension for the back stroke.

one problem that you will have is the suspension. you will need some sore of suspension. your conventional spider will get far too brittle at 180K. you could use copper coil springs like on adires parthenon.

[tomtt]

Originally posted by BassAwdyO
14 guage wire, resitstance, meh. This is why I say all of us clowns ought to stop clowning around with copper and look toward superconductor. Sure you got to keep it cold, but that aint no thang. I dont think it would work so well in voicecoils, but interconnects should be no problem.

I'd like to see how these magnovox speakers work, if they really perform so well. 1930 is old bones!

in this direction -


http://www.acoust.rise.waseda.ac.jp/...4_yamasaki.pdf


at last ...

( with thanks to lrntglls )

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