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Old 2nd May 2005, 08:18 PM   #1
tade is offline tade  United States
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Default Halbach array for true ribbon tweeter.

An Halbach array is a pattern of arranged magnets such that on one side the field strength is augmented, and on the other it is negated. I was wondering if this could be applied to a true ribbon tweeter.
Does the polarity of the magnets on a ribbon tweeter have to be uniform along each side? I believe the field on a halbach array flips from positive to negative every two or three magnets. If it could be used, it would mean that no pole pieces would be necessary, which would be super cool.

here is a halbach array info site:
http://www.matchrockets.com/ether/halbach.html

Here is an only slightly related picture of this afternoon's sonic folley. Proving to myself that ribbon speakers actually work.
Note: the T/S parameters are outstanding. Also that i could melt holes in the aluminum with my amp cranked...
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Old 2nd May 2005, 09:51 PM   #2
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There was an article about this in Scientific American a few years back. I thought it was interesting and wanted to pursue it, but a little thought persuaded me that it was a blind alley...at least regarding ribbons.
A ribbon is a conductor suspended in a transverse magnetic field. The goal is a smooth, unvarying magnetic flux. To change the field north-for-south as you go down the length of the ribbon (admittedly oversimplifying things) will result in some parts of the ribbon moving forward (thereby causing a compression wave), while the others move backward (rarefaction). The end result would be a remarkable reduction in efficiency, since the compression and rarefaction would cancel out and leave you with very little sound at all.
I'm certainly interested if something practical can be worked out. I love ribbons.

Grey
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Old 3rd May 2005, 12:39 AM   #3
tade is offline tade  United States
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grey, makes perfect sense. I had a hunch a poleless true ribbon would be too good to be true. hehe.
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Old 3rd May 2005, 09:02 PM   #4
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It's the very fact that the magnetic flux has a defined North/South direction that makes it work. Now if we could come up with a true monopole, such that we could have a North and a South, then that would be easy to envision...

Grey

EDIT: ...Unless things have changed since I lived up there, Raleigh only has one "i" in it...
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Old 22nd March 2010, 01:19 AM   #5
mightym is offline mightym  United States
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Gray,

Did you ever pursue this?

There's a fellow over at Motoredbikes.com ( a bicycling forum ) who's trying to build a lightweight motor based on Halbach's work.

He's posted some interesting results from his working with F.E.M.M. software. Seem's like the field, although it looses strength, with distance can be made pretty uniform, it just depends on how you stack the magnets....

I'm just curious here.

The OP over there has put it all in one spot without all the banter here:Halbach Disc Motor Project - Motorized Bicycle Racing Network

In case your interested.

he seems to think that he'll be able to get away with double stacking pretty cheap .25" cube magnets for his motor.

John
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