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Old 15th February 2006, 08:48 AM   #1
APi is offline APi  Finland
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Default Nickel ribbon

Have anyone done ribbon by ferromagnetic material like iron, nickel, cobalt or compounds like invar etc?

Pros:
1) Stronger magnetic field than in air gap has.
2) Linear magnetic field.
3) Even ceramic magnets will do. No need for neodyms.
4) Ribbon can be wide and both magnetic flux and linearity can still be excelent.
5) Magnets can be placed many ways to avoid cavity resonance in "air gap".

Cons:
1) Ferromagnetic materials have bigger density and resistivity than aluminum. However bigger magnetic flux compensates that a bit especially in big and wide ribbons.
2) Magnets attract ribbon so that ribbon should propably be mounted at sides too without resonances at used frequency range and that is the BIG problem.

In my opinion iron alloys have too much corrosive problems, cobalt is dirt expensive. Pure nickel seems to be the best if anyone like to test this.

I found that thin nickel foil down to 8um is commercially available. One manufacturer:

Special metals

Any comments?
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Old 15th February 2006, 02:14 PM   #2
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This is a mesuerment of a 30mm wide ribbon whit iron powder on the back side.
Click the image to open in full size.
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Old 17th February 2006, 11:33 AM   #3
APi is offline APi  Finland
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1) How have you solved the problem that magnets pull ribbon covered by iron powder?

2) Did you find that iron powder increase sensitivity compared to traditional ribbon or is it just an extra weight?
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Old 17th February 2006, 12:09 PM   #4
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I wanted the ribbon to get pulled by the magnets.The i ribbon i made is glued the neomagnets.

The main ting is not that you get and increased sensivity but it goes much higer 50 kilo maybe.
Click the image to open in full size.

The "invention" was made by Johnny Sorensen.And printed i a danish magasin called Highfidelity some 15 years ago.
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Old 17th February 2006, 12:58 PM   #5
APi is offline APi  Finland
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Interesting

So you attach both long sides of a ribbon to magnets? Or just one side and let the iron powder and magnets keep the ribbon straight?

Both are good ways to avoid twisting of the ribbon or making wrinkles by misuse. This construction is very strong and stable. Something that I have also tried to do because long full range ribbons are too sensitive for all kind of air movements in a room.

But how does the ribbon move then? It should stretch. There comes few problems I havenīt solve yet:

1) This stretching acts like a spring which try to avoid ribbon movement. It makes a resonant frequency depending on ribbon mass and itīs tensile stiffness. How to construct ribbon so that this frequency is not in band? Especially when having a full range ribbon?

2) Because of stretching, ribbon excursion and SPL are limited and poor?

3) Also ribbon like this bend. Sides doesnīt move but the center does. It makes a kind of cone resonances that should be dambed somehow at joints. How?
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Old 17th February 2006, 01:11 PM   #6
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Both sides are glued.I have corrigated et the other way like this.Then it can move.
Click the image to open in full size.
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Old 17th February 2006, 01:27 PM   #7
APi is offline APi  Finland
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Correction....

2) Ribbon excursion and SPL are limited ONLY IF resonance frequency due tensile stiffness and mass is in band or above.

I doubt that you can make this resonance below, letīs say 200Hz with glued full range ribbon working down to 200-300Hz. Not at least if excursion compared to ribbon width is significant when tensile force increase more than linear as a function of ribbon excursion. Then even 1mm excursion can be too much.

Letīs put it another way... Glued ribbons work but they propably have a lot of resonances and THD and so free ribbon advantages have been lost except line source behaviour.

If you know how these disadvantages can be avoided, I am now extremely interested of your project !!! Especially if ferromagnetic ribbons like nickel or iron powder can be used.
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Old 17th February 2006, 01:43 PM   #8
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This is a measurement of my ribbon.This one does not got iron pouder, but it you can see it can go below 300 hz.It is 20mm wide and 150cm long

Click the image to open in full size.
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Old 17th February 2006, 01:54 PM   #9
APi is offline APi  Finland
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It seem that resonance frequency is not a problem there. Great work!

How have you corrugated your ribbon so that ...
1) ... foil doesnīt ring.
2) ... it stretch enough?

Have you measured what is the maximum excursion at lowest used frequency? And is there a lot of THD when played loud?
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Old 17th February 2006, 03:50 PM   #10
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1. yes and becorse the way the magneticfield put the force on the ribbon

2.yes and it gets very stif'

1 meter long
Click the image to open in full size.
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