Old speakers magnet demagnetization

assimaki · 2nd February 2010, 09:32 AM

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’-70’s and neodymium for 80’s+.
So, do the permaanent magnets have a lifetime? If yes, how long is the time to get difference that is heard?

planet10 · 2nd February 2010, 09:53 AM

Alnico will age with time, mechanical shock or extremes of temperature. Neo will go away under extreme heat. Ferrite i don't know,

dave

assimaki · 2nd February 2010, 10:48 AM

Dear Dave,
The maximum storage temperature was around 42C or 108F (summer periods).
Do you think that my old (60’s 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

AndrewT · 2nd February 2010, 11:24 AM

Alnico rates along with the best at holding it's magnetisation.
Ferrite/ceramic ranks along with the worst at holding it's magnetisation.

Mooly · 2nd February 2010, 11:31 AM

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.

Ron E · 2nd February 2010, 12:05 PM

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.

chinamagnet · 3rd November 2010, 12:34 PM

Ferrite temp. will be steady but not arong as neo

2nd February 2010, 09:32 AM	#1
assimaki diyAudio Member Join Date: Jan 2008 Location: Athens, Greece	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’-70’s and neodymium for 80’s+. So, do the permaanent magnets have a lifetime? If yes, how long is the time to get difference that is heard?

2nd February 2010, 09:53 AM	#2
planet10 diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 4	Alnico will age with time, mechanical shock or extremes of temperature. Neo will go away under extreme heat. Ferrite i don't know, dave __________________ community sites t-linespeakers.org, frugal-horn.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

2nd February 2010, 11:24 AM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Alnico rates along with the best at holding it's magnetisation. Ferrite/ceramic ranks along with the worst at holding it's magnetisation. __________________ regards Andrew T.

2nd February 2010, 12:05 PM	#6
Ron E diyAudio Member Join Date: Jun 2002 Location: USA, MN	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. __________________ Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan Science is a way of thinking much more than it is a body of knowledge. --Carl Sagan

3rd November 2010, 12:34 PM	#7
chinamagnet diyAudio Member Join Date: Nov 2010 Location: china	Ferrite Neo Magnet Ferrite temp. will be steady but not arong as neo


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2nd February 2010, 10:48 AM	#3
assimaki diyAudio Member Join Date: Jan 2008 Location: Athens, Greece	Dear Dave, The maximum storage temperature was around 42C or 108F (summer periods). Do you think that my old (60’s 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

2nd February 2010, 11:31 AM	#5
Mooly diyAudio Member Join Date: Sep 2007	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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