Alnico Demagnetize?

I followed some discussions here and read something about the demagnetization of Alnico magnets.
How does this happen?
What do I have to look for when I buy Alnico baskets?
How can I find out withiut having a Gauss Meter?

Thank you!

Guido

"I followed some discussions here and read something about the demagnetization of Alnico magnets.
How does this happen?"

Alnico magnets can be demagnetized by physical shock, i.e.. dropping the driver, or by having the driver being over driven either by very powerful transients or less powerfully over a sustained amount of time. Probably most pro drivers will show some loss of magnetization by this time as they are often moved and often driven hard.

"What do I have to look for when I buy Alnico baskets?"

Unfortunately there is no visible guarantee of a good magnet, but if you see very obvious physical abuse stay away.

"How can I find out without having a Gauss Meter?"

The only empirical test other than removing the cone and using a gauss meter is to run a series of acoustic tests and compare it with a properly functioning unit.

In woofers the sound can get woolly and their is a loss of HF. In HF drivers the HF rolls off.

I am not sure about Europe, but the good news is that here in the States there are several places that can remagnetize a driver for around $25. The woofer or HF driver need not be disassembled.

Yes be careful when buying baskets ect. Ive found the magnets can easily shift and go out of alignment. Thats factory time. Something to think about. If pushing in on the cone the scraping could be the mags. Ive seen oy all frozen demaged warped you name it.

Hi. I have some questions about this. Does you expert guys recommend the woofers in my 4333A's from 1979 to be remagnetized? What about the 2420 and 2405?

Rolf

Hi, Mr. Widget (and everyone!):

"...in the States there are several places that can remagnetize a driver for around $25. The woofer or HF driver need not be disassembled."

Are you serious?? If this process only costs around $25.00 and doesn't involve disassembly of the driver unit, would my local JBL repair rep be the one to contact for more information? Some lucky JBL repair facility in the Chicago area stands to make $$$ off of me; I have a collection of alnico drivers dating back to the 1950's, some of which are truly starving for regausing.

Regards,
Charley

I don't know if anyone does it in the Chicago area, but I have talked with Orange County Speakers and they quoted me a $25 charge. Woofer or HF driver and no disassembly required. I know I was talking to someone who had their magnets recharged elsewhere in the country, but I don't remember where they were.

http://www.speakerrepair.com/

Anybody in the Mid-Atlantic that can remagnitize? I haven't had any luck finding any one.