ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1]   Go Down

Author Topic: jbl 2268hpl demagnetized??  (Read 4415 times)

Raul Ruiz

  • Newbie
  • *
  • Offline Offline
  • Posts: 3
jbl 2268hpl demagnetized??
« on: November 21, 2015, 02:02:41 am »
Hi anybody ever had a neodymium speaker demagnetize??

I sent a JBL 2268hpl 18" woofer to get reconed and they told me
it could not be reconed because the speaker was demagnetized.
And was told  the speaker was no good anymore. The speaker
had to be replaced. So I had to buy a brand new one.
Anyone ever had this happen? or knows what could of happened to the driver?
« Last Edit: November 21, 2015, 02:10:23 am by Raul Ruiz »
Logged

Bob Leonard

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 6807
  • Boston, MA USA
Re: jbl 2268hpl demagnetized??
« Reply #1 on: November 21, 2015, 07:16:54 am »
Unlike ceramic or ALNICO magnets, Neo suffers from a severe loss of magnetic property when faced with extreme heat. Where other type magnets may "recover", neo will not. However, it takes extreme heat for this to happen and usually, but not always, the motor assembly will fail first. Have I seen this? Yes, but NOT with a JBL driver.
« Last Edit: November 21, 2015, 10:54:30 am by Bob Leonard »
Logged
BOSTON STRONG........
Proud Vietnam Veteran

I did a gig for Otis Elevator once. Like every job, it had it's ups and downs.

Dave Pluke

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1056
    • BIGG GRIN Productions
Re: jbl 2268hpl demagnetized??
« Reply #2 on: November 21, 2015, 10:24:48 am »
Quote from: Bob Leonard on November 21, 2015, 07:16:54 am
Where other type magnets may "recover", neo will not.

This is interesting, and kind of disturbing, news to me.  And by "recover", do you mean it will not accept a re-magnetization?

Perhaps it's better to live with the weight of ceramic or alnico magnets?

Dave
Logged
...an analog man in a digital world [tm]

Flying direct to nearly everywhere out of ATL

Bob Leonard

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 6807
  • Boston, MA USA
Re: jbl 2268hpl demagnetized??
« Reply #3 on: November 21, 2015, 10:53:56 am »
Logged
BOSTON STRONG........
Proud Vietnam Veteran

I did a gig for Otis Elevator once. Like every job, it had it's ups and downs.

Dave Pluke

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1056
    • BIGG GRIN Productions
Re: jbl 2268hpl demagnetized??
« Reply #4 on: November 21, 2015, 11:47:48 am »
Logged
...an analog man in a digital world [tm]

Flying direct to nearly everywhere out of ATL

Art Welter

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1657
Re: jbl 2268hpl demagnetized??
« Reply #5 on: November 21, 2015, 01:41:29 pm »
Quote from: Raul Ruiz on November 21, 2015, 02:02:41 am
Hi anybody ever had a neodymium speaker demagnetize??

I sent a JBL 2268hpl 18" woofer to get reconed and they told me
it could not be reconed because the speaker was demagnetized.
And was told  the speaker was no good anymore. The speaker
had to be replaced. So I had to buy a brand new one.
Anyone ever had this happen? or knows what could of happened to the driver?
Raul,
Sounds like a your reconer is full of it. I have not heard of a reconer checking the flux density of a magnet structure prior to reconing. Ask him what it was (should be .6)
The Neo used by reputable loudspeaker manufacturers has a Curie temperature of 310 to 400C (590 to 752 F) . If you recall "Farenheit 451" is the temperature which paper burns, your speaker would likely have been in flames well before it was demagnetized.

Art
Logged

Jim Rutherford

  • Full Member
  • ***
  • Offline Offline
  • Posts: 208
Re: jbl 2268hpl demagnetized??
« Reply #6 on: November 21, 2015, 07:24:10 pm »
Yes, but what is the upper temp for the speakers?  The reference paper above suggests that the temperature which they begin to weaken could be much lower than the Curie temp. 

JBL doesn't specify a max storage or run temperature.  I would presume that it is significantly high enough to not worry about?
Logged

Bob Leonard

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 6807
  • Boston, MA USA
Re: jbl 2268hpl demagnetized??
« Reply #7 on: November 22, 2015, 11:18:40 am »
This is why Art is calling BS on the re-cone facility. In order to completely demagnetize those drivers it would take excessive heat for very, very long periods of time, or heat to the point the voice coils would burn in a pretty spectacular way. Voice coils get hot, very hot, but properly powered the should never heat to the point of combustion or total destruction. And by the way, the temp we're talking about is capable of making the magnets glow red.

I hadn't considered the re-cone facility might be pulling a fast one here, but now that I think about this I would have to wonder if the re-cone facility was authorized, and if not might have been looking to sell a driver, taking the easy way out.
Logged
BOSTON STRONG........
Proud Vietnam Veteran

I did a gig for Otis Elevator once. Like every job, it had it's ups and downs.

Tim McCulloch

  • SR Forums
  • Hero Member
  • *
  • Offline Offline
  • Posts: 20992
  • Wichita, Kansas USA
Re: jbl 2268hpl demagnetized??
« Reply #8 on: November 22, 2015, 11:52:10 am »
Quote from: Bob Leonard on November 22, 2015, 11:18:40 am
This is why Art is calling BS on the re-cone facility. In order to completely demagnetize those drivers it would take excessive heat for very, very long periods of time, or heat to the point the voice coils would burn in a pretty spectacular way. Voice coils get hot, very hot, but properly powered the should never heat to the point of combustion or total destruction. And by the way, the temp we're talking about is capable of making the magnets glow red.

I hadn't considered the re-cone facility might be pulling a fast one here, but now that I think about this I would have to wonder if the re-cone facility was authorized, and if not might have been looking to sell a driver, taking the easy way out.

Raul doesn't say where he's located, but if he sends the speaker back to JBLfor reconing, they can easily remagnetize the motor.
Logged
"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Ivan Beaver

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 8968
  • Atlanta GA
Re: jbl 2268hpl demagnetized??
« Reply #9 on: November 22, 2015, 01:11:26 pm »
Quote from: Tim McCulloch on November 22, 2015, 11:52:10 am
Raul doesn't say where he's located, but if he sends the speaker back to JBLfor reconing, they can easily remagnetize the motor.
Yeah-that is a quick simple 2 or 3 second job-IF you have the right tools.

And they could evaluate it and see IF it lost it magnetic strength and possibly why.
Logged
A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

ProSoundWeb Community

Re: jbl 2268hpl demagnetized??
« Reply #9 on: November 22, 2015, 01:11:26 pm »

Pages: [1]   Go Up
« previous next »
 



Page created in 0.05 seconds with 25 queries.