question on the speakers magnets

[Derry]

I removed the magnet cover off the back of the 15" woofer and see a large aluminum color surface almost as big as the cover itself,, is this just covering the magnet or is it part of the actual magnet,, photo below,,

when I place a screwdriver next to it there is very little attraction,, have read here on the forum about having them recharged,,

what about the magnet in the horn, are the of the same character losing their strength with age,, reminds me of my own body,,

the magnets in my old AR2As that I just reworked from the late 60s, I could hardly pull the screwdriver off those 11" woofers and can't imagine them being much stronger when new,,

thanks

Derry

[bowtie427ss]

By removing the outer cover, you have exposed to view the "magnetic return pot" which actually completes the magnetic circuit, and also incidentally prevents most stray magnetic fields, hence most Alnico assemblies are effectively "magnetically shielded" and are generally safe to use around magnetically sensitive devices like CRT's etc.. The actual magnet proper is buried deep in the structure. Disassembly of the structure will usually result in near full discharge of the magnet.

[Altec Best]

when I place a screwdriver next to it there is very little attraction,, have read here on the forum about having them recharged,,

what about the magnet in the horn, are the of the same character losing their strength with age,, reminds me of my own body,,

the magnets in my old AR2As that I just reworked from the late 60s, I could hardly pull the screwdriver off those 11" woofers and can't imagine them being much stronger when new,,

thanks

Derry

Hi Derry, should also try to refrain from allowing srewdrivers or any other metal to slap up against the magnets.The ferrite magnets are quite brittle although yours are Alnico V it is just not a good idea to do that.

If you feel the magnets are weak or they just don't sound the same as new there is only one place to send Altec stuff Great Plains Audio !!!


Very,Very, nice people there.:2thumbsup:

[robertbartsch]

Alnico magnets can loose some strength but I believe it is not related to their age. Rather, for alnico's, it is a function of taking large hits of current from power amps and the power loss can result in 3 or 4 db loss in SPL.

The "other" Lansing cite has an informative thread on alnico and ferrite magnets:


The Great Alnico / Ferrite Debate


For HF horn drivers, I don't believe the mags are sheilded in the area of the diaphragm, so don't even think of getting a screw driver or other metal tool close to the frame without precautions. Its really best to have professionals change diaphragms (like GPA), if necessary.

...Enjoy the read!

[Old Guy]

Alnico magnets can loose some strength but I believe it is not related to their age. Rather, for alnico's, it is a function of taking large hits of current from power amps and the power loss can result in 3 or 4 db loss in SPL.

Impact also can discharge Alnico.