Old speakers magnet demagnetization

[assimaki]

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]

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]

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]

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

 

[Mooly]

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]

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]

Ferrite Neo Magnet

Ferrite temp. will be steady but not arong as neo