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Old 2nd February 2010, 09:32 AM   #1
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Default Old speakers magnet demagnetization

I own some old speakers and I am wondering if they are demagnetized due to their age.
I searched for scientific articles but it was not possible to get any clear answer.
I suppose that the magnets are made of alnico for the 60-70s and neodymium for 80s+.
So, do the permaanent magnets have a lifetime? If yes, how long is the time to get difference that is heard?
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Old 2nd February 2010, 09:53 AM   #2
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Alnico will age with time, mechanical shock or extremes of temperature. Neo will go away under extreme heat. Ferrite i don't know,

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Old 2nd February 2010, 10:48 AM   #3
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Dear Dave,
The maximum storage temperature was around 42C or 108F (summer periods).
Do you think that my old (60s telefunken) speakers could be demagnetized?
I am talking about important difference, more than 10%.
I suppose that -1 to -2% has no impact to the final result.
Thanks
Michalis
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Old 2nd February 2010, 11:24 AM   #4
AndrewT is offline AndrewT  Scotland
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Alnico rates along with the best at holding it's magnetisation.
Ferrite/ceramic ranks along with the worst at holding it's magnetisation.
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Old 2nd February 2010, 11:31 AM   #5
Mooly is offline Mooly  United Kingdom
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I would imagine checking the sensitivity of the speaker would be a possible test... does it meet it's SPL @1meter rating. Hardly practical to test though.
Can't say I have ever come across the issue.
And even using a large degauss wand on an old magent doesn't seem to alter it noticeably.
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Old 2nd February 2010, 12:05 PM   #6
Ron E is online now Ron E  United States
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What types of magnets are there?

Alnico are easiest to demagnetize
Ceramic have low Br, which is why they need to be bigger/differently shaped.
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Old 3rd November 2010, 12:34 PM   #7
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Default Ferrite Neo Magnet

Ferrite temp. will be steady but not arong as neo
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