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Author Topic: Field Coil Loudspeakers?  (Read 3088 times)

Frederik Rosenkjśr

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Re: Field Coil Loudspeakers?
« Reply #10 on: December 03, 2012, 12:27:33 pm »

> I wonder however what would happen if there were essentially two coils, the inner voice coil, and an outer field coil that were both wired to the same amplifier power output with their polarities reversed as to provide double the push / pull in either direction? In theory this would produce double the heat, but it would allow for a passive speaker design in which the only power needed would be that from the standard amp much like any other speaker.


If you vary both the field strength and the VC voltage, they will multiply. The result would be a cone excursion that would equal the voltage squared, instead of having a linear relationship.

Might be interesting to hear, sort of a downward expander set to ridiculous settings.

Gene

This sounds like something that could be dealt with via DSP? Could be interesting - very lightweight speakers...
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Don Boomer

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Re: Field Coil Loudspeakers?
« Reply #11 on: December 03, 2012, 05:52:48 pm »


I wonder however what would happen if there were essentially two coils, the inner voice coil, and an outer field coil that were both wired to the same amplifier power output with their polarities reversed as to provide double the push / pull in either direction?

I'm not sure that you wouldn't get the same thing by just double layering the VC??

There are speakers that use differential VCs currently in production from JBL and Peavey (maybe others) that are along the lines of what you are describing that achieve much lower distortion specs from the differential pair of VCs.
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Don Boomer
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Sam Feine

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Re: Field Coil Loudspeakers?
« Reply #12 on: December 03, 2012, 09:22:26 pm »

I'm not sure that you wouldn't get the same thing by just double layering the VC??

There are speakers that use differential VCs currently in production from JBL and Peavey (maybe others) that are along the lines of what you are describing that achieve much lower distortion specs from the differential pair of VCs.

Your right, not exactly the same, but similar concept using traditional permeant magnets.

http://www.jblpro.com/pub/technote/JBL_TN%201-33%20rev3.pdf
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David Morison

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Re: Field Coil Loudspeakers?
« Reply #13 on: December 04, 2012, 08:14:57 am »

I'm not sure that you wouldn't get the same thing by just double layering the VC??

Surely the Voice coil would have to be able to move relative to the Field coil though, otherwise nothing will happen bar heat?
Unless I'm completely misunderstanding you of course!!!

Edit: un-typo'd
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Ed Walters

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Re: Field Coil Loudspeakers?
« Reply #14 on: December 04, 2012, 03:14:16 pm »

Surely the Voice coil would have to be able to move relative to the Field coil though, otherwise nothing will happen bar heat?
Unless I'm completely misunderstanding you of course!!!

Edit: un-typo'd

This would be an interesting experiment with one of the dual coil/differential drive speakers now available. Drive the two coils in series but out of phase; the only audio would be the sum of their nonlinearities...ie distortion.

Back to the field coil speaker, though...a little cocktail napkin calculation shows that to get similar magnetic fields as to that in a modern speaker would require about 150 feet of 12 or 14 gauge wire, coiled up in a four inch coil, two inches high.  Or fewer turns/feet and a LOT more current (and with it heat). Numbers based on typical four inch voice coil, 400 watts drive, approximately 16 Tesla field in a typical woofer.  It won't fit. It's not doable in a practical sense.

/Ed
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paul bell

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Re: Field Coil Loudspeakers?
« Reply #15 on: December 05, 2012, 12:07:26 am »

> I wonder however what would happen if there were essentially two coils, the inner voice coil, and an outer field coil that were both wired to the same amplifier power output with their polarities reversed as to provide double the push / pull in either direction?

I actually tried this some years ago. The idea was to have a "magnetless speaker"

A voice coil needs to be immersed in a pretty strong magnetic field with it's flux focused in an oval from top to bottom of the voice coil.

Two voice coils each receiving the same power level would not cause either one to attain any motion.

Even if one of these coils had a higher power level fed to it, it's still substantially too low in power to create a magnetic field to get the other coil to react. Plus the issue of not having an iron pot to focus the field.

The well designed high powered ferrite and neodymium loaded modern speakers we have on the market today are far away better than any field coil speaker could be.
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paul bell

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Re: Field Coil Loudspeakers?
« Reply #16 on: December 05, 2012, 12:16:12 am »

I always felt the best magnets for long excursion woofers was a radial neodymium design, like used in the Aura/Barry woofer and the NeoMax woofer. I wanted to see how that design would be with a dual radial design, neodymium strips outside the voice coil AND inside the voice coil.
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Jim McKeveny

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Re: Field Coil Loudspeakers?
« Reply #17 on: December 05, 2012, 06:41:46 am »

The Aura 1808 was my go-to for custom subwoofers in the 1990's. It modeled and performed like nothing else available. The TC Sounds Pro 5100 is a virtual clone, but some conventionally magneted competitors now match its performance at lower cost.

The radial magnet orientation & extreme excursion seemed to confuse the "offset integrator" on Crown MA5000's, and it needed to be disabled for proper function. Great cone. Loopy Bozeman.
« Last Edit: December 05, 2012, 06:29:41 pm by Jim McKeveny »
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paul bell

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Re: Field Coil Loudspeakers?
« Reply #18 on: December 05, 2012, 07:48:52 am »

Loopy Bozeman.

Oh yeah!

My testing of these woofers didn't have very good results. The following were the issues found:

-The solder joints on the coil former melted.

-The copper pole sleeve wandered out towards the dust cap.

-Barry Bozeman.
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Jim McKeveny

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Re: Field Coil Loudspeakers?
« Reply #19 on: December 05, 2012, 10:15:59 am »

My experiences post-AURA mimic yours.
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