AlNiCo vs. Neodymium

[Timn8ter]

Inspired by another thread I thought it would be interesting to discuss the merits of AlNiCo magnet structures in drivers versus Neodymium. Compared to other magnets (ferrite, ceramic, etc.) AlNiCo has major benefits (except cost) but when compared to Neodymium does it fail to match up? Especially when Neodymium is less expensive?

[jcarr]

Tim: Have you read this older thread?

http://www.diyaudio.com/forums/showt...628#post146628

jonathan carr

[Nelson Pass]

It would appear from the Lowther experience that Neodymium
might in fact be superior to Alnico in that it delivers the same
high field strength, but I am also told that the field fluctuates
less against voice coil action. I suppose that it would be thought
of as "stiffer" in this regard.

[Salas]

It suffers some thermal compression issue though. Ventilation must be augmented and chasis redesigned. Also the omnipresent Chinese Nd does not make the proper purity grade and suffers nonlinearities . Good Nd costs dearly and I doubt its used anywhere else than in first class European and American compression drivers and top quality prof big power woofers. Not sure about the Nd quality in FarEast sourced ribbons that are used a lot in projects lately.

[jlsem]

Tim: Have you read this older thread?

Jonathan,

Is platiron related to Allegheny Ludlum's Platinum-Colbalt magnet material? I'd always considered this to be the most promising material for speaker motors with six times the coercive force of Alnico V and eminent workability to boot. However, being 77% platinum and 23% cobalt, practical application is out of the question.

John

[Timn8ter]

Originally posted by jcarr
Tim: Have you read this older thread?

http://www.diyaudio.com/forums/showt...628#post146628

jonathan carr

Missed that one, thank you Jonathan. It does shed some light on my question. It seems since that thread was posted there are more Neo drivers on the market including the latest XBL^2 offerings from Adire and CSS.
(from the Adire site)
" The Extremis 6 uses a neodymium magnet system which is inherently low in stray flux. In fact, the stray field just 2" from the motor is less than 100 mG (the Earth's magnetic field is 5 times larger!)"

[Ken L]

Originally posted by Timn8ter
but when compared to Neodymium ...........

another advantage to Nd is that for comparable strength (gauss) it takes up less space - and by so doing allows for different physical configurations that cannot be physically achieved with Alnico.

Regards

Ken L

[jcarr]

John:

>Is platiron related to Allegheny Ludlum's Platinum-Colbalt magnet material?<

It could be, although to the best of my knowledge, Platiron is a material developed at a Japanese university. The patent was later licensed to Nippon Mining (which subsequently became Japan Energy), but the manufacturing rights were subsequently revoked.

The platiron that I used was 70-some percent platinum and the remainder was largely iron (hence the acronym PLATinum-IRON), but certainly the percentages are in the general ballpark as the Allegheny Ludlum material. Do you have a link or an email address for that? I did a quick Google, but didn't see anything.

>However, being 77% platinum and 23% cobalt, practical application is out of the question.<

If it is as powerful as the platiron, you may not need all that much of it (at least if you don't insist on making a woofer from it. And it could be dandy for phono cartridges.

Unfortunately, just like Alnicos, you will almost certainly have to use polepieces with these platinum magnets.

The next task would be find someone who makes 99.999% or 99.9999% pure iron for suitably exotic polepieces to go with the platinum.

FWIW, the magnets that I use in my current designs are NeoMax 50 and NeoMax 52 (made by Sumitomo). I use these in open-circuit pairs (without polepieces).

regards, jonathan carr

[thomas997]

Originally posted by salas
Good Nd costs dearly and I doubt its used anywhere else than in first class European and American compression drivers and top quality prof big power woofers. Not sure about the Nd quality in FarEast sourced ribbons that are used a lot in projects lately.

TB uses it in this driver: http://www.tb-speaker.com/detail/1208_03/w3-926s.asp

About 14$ each in quantity.

I dont know if its "good" or not though.

[jlsem]

The next task would be find someone who makes 99.999% or 99.9999% pure iron for suitably exotic polepieces to go with the platinum.

Is Armco zone-refined iron not pure enough for a large speaker? I would like to try a field coil type motor using Armco as the core and the pole pieces. Throw in Ohno CC copper wire for grins.

John