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Old 6th July 2004, 09:00 AM   #1
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Join Date: Feb 2002
Location: Germany
Lightbulb Nd doping of ferrite magnet drivers

Neodym magnets appear preferable over ferrite magnets mainly because they promise to offer lower distortion. However, Nd designs are usually optimized for PA applications, so the drivers would not always have the desired properties for home applications. What is more, these drivers are usually optimized for low weight and high sensitivity, not necessarily low distortion which requires the iron near the gap to be driven into saturation.

Tuning an off-the-shelf driver that comes with a ferrite magnet and has no or insufficient short-circuit sleeving and testing for distortion reduction has been a thing that I have wanted to to for a while. However, chipping away the whole ferrite magnet would require removal of the spider/cone assembly so that the gap can be cleaned. What is more, centering the pole pieces with charged Nd magnets in place would be more than challenging.

Now I have had a different idea:
- cover all openenings (pole vent, spider vent, VC vents) with masking tape
- machine pockets into the circumference of the ferrite magnet, ideally going from pole plate to pole plate, but leaving some ferrite further inward so that the gap is still sealed
- put Nd magnets into the pockets

Considering that modern Nd magnets have 10x higher flux density than ferrite and that most driver designs operate the iron at 70-90% of saturation flux, replacing only 1/10 of the ferrite with Nd would suffice to drive the iron well into saturation. If the iron near the gap is driven too far into saturation, there is a danger that the stray field causes an assymetry even of the field inside the gap. If even more Nd is used so that even the top and bottom plates near the magnet can no longer carry the field, the Nd-magnets' field would return through the ferrite, neutralizing the ferrite, which is also not desirable.

Now my questions are:
- Is ferrite too brittle or too hard to be machined with a router bit?
- Is ferrite dust toxic? I suppose not because ferrites are not protected against chipping or rubbing.
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Old 6th July 2004, 11:56 AM   #2
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Join Date: Jun 2002
Location: Melbourne, Australia
Default Re: Nd doping of ferrite magnet drivers

Originally posted by capslock
- Is ferrite too brittle or too hard to be machined with a router bit?
Ferrite is hard like ceramic so I expect you would have to use some kind of small grinding wheel.
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Old 6th July 2004, 01:10 PM   #3
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What is a grinding wheel? One of those tiny discs (maybe 10 cm dia., 3 mm thick) that you can use to cut steel or ceramic tiles?
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