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Old 24th February 2004, 11:45 AM   #1
tuneman is offline tuneman  Australia
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Default pole piece material?

im am curious to know what steel is required to make pole pieces top/back plates etc? i've always assumed it is a very hight carbon steel is this correct?

also if one were to make a pole piece out of solid copper what would happen? taking into account eddie currents etc
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Old 25th February 2004, 08:40 PM   #2
sreten is offline sreten  United Kingdom
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You can't make a pole piece out of copper as its non-magnetic.

High carbon steel is required for extreme hardness, a factor
I can't see any relevance to the application. Stainless steel,
obviously, the only other relevant parameter I'd guess is
maximum flux density before saturation.

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Old 25th February 2004, 09:10 PM   #3
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Steel or iron. Strontium ferrite perhaps?
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Old 25th February 2004, 09:22 PM   #4
sreten is offline sreten  United Kingdom
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AFAIK except for high performance units pole pieces are made
of soft iron, pure enough or with enough additives to prevent
it rusting.

Copper plating is one way of adding Faraday rings.

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Old 25th February 2004, 09:51 PM   #5
markp is offline markp  United States
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Most stainless steel is non-magnetic or a very poor magnet.
If it sounds good... it is good!
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Old 25th February 2004, 10:40 PM   #6
Mark Kravchenko
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Default Iron is best

The lower the carbon content the better. Stainless is a poor choice as it is a poor magnetic conductor. Generally 1010 steel is used in production drivers. Normal mild steel is 1018 and suffers a bit in the total possible flux level it can support.

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Old 25th February 2004, 10:42 PM   #7
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Exactly. Low carbon content; 1006 if you can get it, 1008, 1010, or 12L14 are acceptable grades as well.

Dan Wiggins
Adire Audio
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Old 25th February 2004, 11:49 PM   #8
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I think they have a 1005 grade as well.

I suppose if one had enough money on hand, they could build pole pieces out of Permendur (iron/cobalt), which, IIRC, handles the highest flux density of all alloys.
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Old 26th February 2004, 05:49 AM   #9
Wizard of Kelts
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Here is some info from a very interesting fellow on pole pieces and loudspeaker magnetics in general:

Here is the link to the general site. Well woth having a look around:
"A friend will help you move. A really good friend will help you move a body."
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Old 26th February 2004, 06:27 AM   #10
jcarr is offline jcarr  United States
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For MC cartridges I've designed and use polepieces made of Permendur as well as soft iron and chemically purified iron (which is about 4~5 times the cost of permendur). For a variety of reasons, I like chemically purified iron the best. Subjectively I like how it sounds better than Permendur, and if you are willing to invest in electro-chemical machining, you can make some pretty precise and intricate polepieces shapes. If you choose Permendur, you will most likely be limited to fairly basic polepiece shapes.

Mind you, the comparatively small size of the magnets used in MC cartridges means that the polepieces are not being pushed to anywhere near saturation limits, even when using something like Neodymium 50.

regards, jonathan carr
http://www.lyraconnoisseur.com/, http://www.lyraaudio.com
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