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View Full Version : alnico magnetic field, how long does it last and what kills it?



jbl_daddy
01-16-2011, 04:39 PM
Alnico magnetic fields, how long do they last, how can you tell when they ar
e weak and how do you recharge them. Just wondering for shits and giggles.

Audiobeer
01-16-2011, 08:41 PM
Dropping an alnico driver effects the alnico magets I'm told. :(

hjames
01-16-2011, 08:47 PM
Alnico magnetic fields, how long do they last, how can you tell when they are weak and how do you recharge them. Just wondering for shits and giggles.
Play them too loud for too long and the coil & magnet gets hot and looses flux ...
Do that too often and you've cut down your driver's response ...
Tho I suspect that was more a problem in club & commercial installations than it would be in our home systems.

The solution to demagged drivers is to get them remagnetized by a pro shop to get them back up to spec..

jbl_daddy
01-17-2011, 07:17 AM
Mine are in great condition but I have wondered about them as they are approaching forty years old. 4340's that is.

Lee in Montreal
01-18-2011, 12:34 PM
Play them too loud for too long and the coil & magnet gets hot and looses flux ...

That's good to know. Alnico drivers risking more to loose flux in commercial use vs home duty.

BTW I shipped your parts. You shall get them them in a couple of days. ;-)

toddalin
01-19-2011, 10:57 AM
I had OCS recone three AlNiCo 2205s as 2235s and had the magnets recharged. The woofers looked like they had seen their fair share of abuse.

Over a year later Grumpy and I tested one on WT-2 and it tested just as a 2235 should, but IIRC the BL was 18-19. (IIRC, spec calls for 20.)

I took them back to OCS who recharged the magnets again (no charge for the re- re-charge :o:). Grumpy came over and we retested the same one and the BL was now 22-23. These are used in my home system and had not seen "serious" power since the recone and OCS swears that the magnets were shot the first time around.

louped garouv
01-19-2011, 02:45 PM
I had OCS recone three AlNiCo 2205s as 2235s and had the magnets recharged. The woofers looked like they had seen their fair share of abuse.

Over a year later Grumpy and I tested one on WT-2 and it tested just as a 2235 should, but IIRC the BL was 18-19. (IIRC, spec calls for 20.)

I took them back to OCS who recharged the magnets again (no charge for the re- re-charge :o:). Grumpy came over and we retested the same one and the BL was now 22-23. These are used in my home system and had not seen "serious" power since the recone and OCS swears that the magnets were shot the first time around.

that's quite interesting....

yggdrasil
01-20-2011, 12:14 AM
Here's some interesting stuff: http://www.audioheritage.org/vbulletin/showthread.php?4031-The-Great-Alnico-Ferrite-Debate

allen mueller
01-20-2011, 04:04 AM
I had OCS recone three AlNiCo 2205s as 2235s and had the magnets recharged. The woofers looked like they had seen their fair share of abuse.

Over a year later Grumpy and I tested one on WT-2 and it tested just as a 2235 should, but IIRC the BL was 18-19. (IIRC, spec calls for 20.)

I took them back to OCS who recharged the magnets again (no charge for the re- re-charge :o:). Grumpy came over and we retested the same one and the BL was now 22-23. These are used in my home system and had not seen "serious" power since the recone and OCS swears that the magnets were shot the first time around.

When you first got the drivers back a year prior to measuring 18-19 what was the measured BL? With out that # its hard to say if the field actually decreased over 1yrs time.


AL

toddalin
01-20-2011, 10:00 AM
No reason that the field should have decreased over a year in home use. Maybe multiple "shots" yield better results than a single shot? :dont-know:

badman
01-20-2011, 11:02 AM
No reason that the field should have decreased over a year in home use. Maybe multiple "shots" yield better results than a single shot? :dont-know:

Possible. Or variance in measuring? Or you DID zap it with too much zoot?

grumpy
01-20-2011, 12:10 PM
IIRC, the one unit was simply inadequately charged... probably not
measured before/after at the vendor. Consistency of the BL measurements
using WT2 was quite high (multiple runs were used to establish this, as I
typically don't trust measurement instruments without question).

Doctor_Electron
01-24-2011, 01:17 AM
Exposure to excessive heat from any cause is not good for most magnet types.

As an aside, I have an old 2402 that was given to me. I had some new diaphram kits in the shop, so for the heck of it I put one in it.

Its acoustic ouput is just sbout nil. But then again, it is one of the better sounding 2402's, as I recall hearing them over the years... ;)

I wound up bead-blasting and giving it a real nice paint job. It is now very cool looking, in wrinkle black (rear section) and satin black on the horn & dome. I get a lot of questions about it from visitors.

It is still very heavy.

more10
01-29-2011, 03:05 PM
I had my 076 and a 2220A without cone checked and recharged this week. The 2220A had lost 20%, the 076 had lost 4%. I have no idea if they have been recharged before.