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interesting speaker damage....

Discussion in 'Amps and Cabs [BG]' started by toobalicious, Apr 22, 2009.


  1. toobalicious

    toobalicious

    May 6, 2008
    triad, nc
    ive never seen one break like this before...

    from a friends POS fender 4x12 (the ones we all love to hate). one of the speakers had lost considerable volume. upon moving the cab, we heard something rolling around in it.

    STA75316.

    the ceramic was almost cleanly fractured in half. mustve experienced some pretty serious trauma, as i cant believe the force was enough to overcome the magnetism, which is considerable. unbelievably, the speaker still works--- the voice coil is intact. it has perhaps 5-10% of the output of the others though, lol.

    STA75317.

    thought about trying to put the sandwich back together, but the magnet strength suggests that would be nearly impossible, at least while retaining motor alignment.

    just thought i would share this anomaly...
     
  2. gregoire1

    gregoire1

    Oct 19, 2008
    Nashville
    Very odd! If you try to put the magnet halves back together, do they repell each other?
     
  3. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Stuff happens. I have removed the magnets from a failed speaker and it took a lot of work. Replace the speaker and get on with life. The whys don't matter as much as getting the cabinet back into service. Buy exactly the same speaker as came out.

    Paul
     
  4. gregoire1

    gregoire1

    Oct 19, 2008
    Nashville
    Sorry BassmanPaul, I gotta know why.
     
  5. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    The why is a cheap poorly made loud speaker. Probably a double magnet motor and a poor glue job. While this has never happened to me or any of the equipment I've worked on I have heard of it happening before. Double magnets should stick together N to S. Home theater speakers have two magnets too. N to N or S to S which cancel each other out externally and don't mess up CRT screens

    Paul
     
  6. toobalicious

    toobalicious

    May 6, 2008
    triad, nc
    actually, the halves attract each other. strong enough attraction, even, that they are hard to separate by hand. that is what makes the scenario so weird. only thing i can figure is that it fractured from some sort of trauma (moving? cold?) and subsequently blew the back half off as it was played.

    the break is clean, but not so clean as to suggest glued-together magnets, which this one isnt, as near as i can tell.

    not sure that exact replacement makes sense, as it is a 70's vintage oxford. while i am fairly certain that one could be found, i cant imagine there are too many pro speakers (that didnt come from pyle, seismic, or shredz, that is) which would or could be bested by the oxford, fender enclosure notwithstanding (which is, as we know, already pretty distant from "ideal").

    cheap and poorly made, indeed! :crying:
     
  7. seamonkey

    seamonkey

    Aug 6, 2004
    Fun! Thanks for sharing.
    Is that rust on there?
    Maybe water seeped in, froze, and broke it apart?
     
  8. MIJ-VI

    MIJ-VI Banned Supporting Member

    Jan 12, 2009
    If this driver was in one of those CBS-era, cross-fire 4X12" particle board (insert expletive) 'bass' cabs, maybe it commited suicide. :D
     
  9. hrgiger

    hrgiger

    Jan 11, 2009
    Ole Jim dropped that magnet at the factory before he installed it...
     
  10. It happens, material failure, crack has probably been there for years and just propagated. If the magnet holds on pretty well even with the crack, I'd question your friends care and handling of his equipment (and keep him away from yours :p )

    Not too similar, but a couple years back I had a custom pickup made. On arrival I installed it into my SG, amazing sounding pickup with one problem, the sound of the D string was almost non-existant. Brought it up with the pickup builder who said to send it back to him. The pole of the D string had fractured almost half way down, just magnetism holding it in place. It got replaced and sent back up and works fine now. Certainly can happen anyway!
     
  11. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    That's because of the reduced magnetic flux. If you could somehow re-attach the magnet, (even temporarily as a fun little experiment), the return the full strength magnetism should result in that speaker sounding fine.
     
  12. toobalicious

    toobalicious

    May 6, 2008
    triad, nc
    suicide, lol...

    yeah, 4x12 angled baffle sort of deal (hence the remark about the "ones we all love to hate"). dude is in a blues band, so the 135 rig actualy did ok for him. they arent really loud, and the $hitty response of that cab just adds... cough... MOJO.

    petebass, i have tried to "set" the broken half about a dozen times, but i couldnt get the alignment right, and the voicecoil didnt move freely. i never applied power, because it wouldve just self destructed. but yea, fun experiment, as may be trying to "use" it in its current, terribly inefficient state. at least until it smokes, i guess. que sera sera.
     
  13. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Thing about using the speaker without the pole piece in place is that the inductance of that speaker is going to be way off. That might just cause your amplifier some problem.

    Paul
     
  14. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Really? I might be wrong here but I though the inductance was more a result of the voice coil winding acting like an inductor. If that's in tact, then inductance should stay the same. And even if it doesn't, I'd expect a change in the frequency response in the highs and high mids but nothing dangerous to the amp.
     
  15. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Think of a transformer with iron laminates. Remove the iron and you have an air core. If you then look at inductors for speaker crossovers. The higher value inductors are wound on cores.

    Paul
     
  16. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    I'm not a transducer expert, but off the top of my head I don't think you can equate a loudspeaker magnet with an iron core.

    I've seen magnets break off of drivers. Be very careful if you try to put the broken off piece back in place; if you get a fingertip in between you may be surprised how much force a speaker magnet can crush with.
     
  17. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    It's not the magnet per se but the broken piece is carrying the pole piece with it so the VC becomes an air core.

    Paul
     
  18. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Oh yeah, I missed the pole piece.
     
  19. Jim Carr

    Jim Carr Dr. Jim Gold Supporting Member

    Jan 21, 2006
    Denton, TX or Kailua, HI
    fEARful Kool-Aid dispensing liberal academic card-carrying union member Musicians Local 72-147
    It was dropped.
     

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