"Magnet slipped" says the Expert; Surround Repair; Poor sound now - Page 2 - diyAudio
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Old 2nd March 2011, 05:41 PM   #11
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by JMFahey View Post

If you pull Alnico from its frame, it loses 60 to 90% of its magnetism, that's what happened to you.
I'm not sure alnico's like the shock from hard bumps either

apart from that, maybe also way too much glue between magnet and poles
optimally you need metal to metal contact
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Old 24th July 2012, 12:06 PM   #12
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I've used an auto body hammer (plastic ends) to tap the magnet realigned before. that's why I recently purchased a pair of Polk Monitor 4 at the thrift store ($7) when I knew they had been dropped. the cones aren't moving but they are putting out weak midrange. I'll check back after I remove the cone dust cover and begin centering it again!
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Old 23rd October 2012, 04:23 AM   #13
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Just harking back to this old thread.

I made a little Hall Effect sensor (glued the sensor onto the end of 6mm dowel), and plugged it into my multimeter. The voltage from the Hall sensor as I passed it through the vent at the rear of the speaker magnet) from the "damaged" speaker was about 60 or 65% of the voltage developed by the good speaker.

That explains the poor performance of this speaker. I must now bid it farewell.

Chaps, many, many thanks for the excellent and detailed information you have provided to me. Looking at one or two of the posts it looks like some of you must have worked in a speaker manufacturing company. Very impressive.

Regards,
George.

P.S. Farmer Jack, my avatar is Sergent Schultz, who knew "nothing, nothing!"
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Old 23rd October 2012, 12:35 PM   #14
JMFahey is offline JMFahey  Argentina
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Well, considering it *is* a JBL, maybe you might make one last effort.
I see you are in Australia.
Where exactly is anybody's guess
I know that there used to be a few speaker factories; at least one ("ex-Celestion branch?) is often mentioned as still active, although quite reduced in size.
Any factory needs a magnetizer.
Maybe you can contact one and send the speaker to be remagnetized for a small fee.
When I started making speakers, I always visited one of them, with no pressure, abig smile and, just by "sheer chance", a couple of "longnecks" under my arm.
"Longneck" being slang for a bottle of *good* wine.
Never failed.
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