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Shifted Magnets!?:(

Discussion in 'Amps and Cabs [BG]' started by father of fires, Mar 6, 2013.


  1. father of fires

    father of fires Commercial User

    Nov 29, 2006
    BALTIMORE CITY
    Chief of Medicine at Damnation Audio
    I have a beat up old Ampeg 8x10. Recently after a show I noticed that only three speakers were working.

    I took the cab apart this weekend a found that some speaker solder joints had broken loose. I also found that two of the speakers had stiff cones. They would not budge at all.

    I called a speaker tech I've used before and he thinks that the magnets have shifted.

    The cab has undoubtedly taken a lot of hits in its time. I only noticed the bum speakers after I let someone use my cab. I bought the crappy 8x10 so I wouldn't have a problem sharing the cab with other bassists. He used a B4R but I don't think he blew anything. I'm just thinking they are just old and their time had come.

    Anyone have a similar issue?

    The tech said it would be about $70 per speaker ($140 total)to fix them. I'm not sure what I want to do. I'd hate to invest the money in worn out old speakers. But it is slightly cheaper than buying decent new ones. Maybe I could buy a kit and try to recone them myself.

    I sort of know who the guy who used my cab last is but I don't see how he could have caused this. Plus its not in my nature to come looking for money. I knew the risks when I lent it to him.

    I'm more frustrated than anything and really just wanted to vent.

    So to sum up....$#^%$&#^$&^%#&%$@&%!!!*^%$*&^%$
     
  2. Mr. Foxen

    Mr. Foxen Commercial User

    Jul 24, 2009
    Bristol, UK
    Amp tinkerer at Ampstack
    Think voice coils distorting and jamming is more likely than shifted magnets. Lots depends on what the speakers in there are. Eminence B810 are the go to nice replacements, and you can sell the working ones to someone who only has a couple of duds, and the not working ones to someone who can sort fixing them.
     
  3. father of fires

    father of fires Commercial User

    Nov 29, 2006
    BALTIMORE CITY
    Chief of Medicine at Damnation Audio
    That makes sense. Shifted Magnets sound like it would have needed to be dropped or something.

    It slid off a step a while back and cracked a caster (which I still need to replace) but it worked flawlessly for months.
     
  4. If the magnets are shifted, then the speakers are toast. To realign a magnet and recone it would cost more than a replacement speaker. It sounds like your buddy could have fried the cab. A B4R bridge into 4 ohms is 1000watts, definitely too much juice for an older 810, particularly if it's a flatback. That amount of power could also have produced enough internal vibration to break the solder joints loose too. A frozen cone could be a shifted magnet or a blown speaker. He should have reported the defects after he borrowed it, but good luck getting any cash from him.
     
  5. I have seen the bonding fail many times before and the magnets will shift locking the cones. It would be better at that point to just replace the speaker.
     
  6. father of fires

    father of fires Commercial User

    Nov 29, 2006
    BALTIMORE CITY
    Chief of Medicine at Damnation Audio
    I will add that I was at the show (I played right before the other guy) and I thought it sounded fine for both of us. He wasn't too loud.

    It's not a flat back. It's an 80's-ish model.
     
  7. Daveydude

    Daveydude Supporting Member

    Feb 27, 2009
    Ft. Lauderdale FL
    I've had a magnet shift on me. It was a newer Fender Pro 215.
    Bought it used with a few hours on it. Everything was fine for about two months or so. I never abused or dropped it. The tech told me the magnet shifter ever so slightly. $75 bucks to fix. It sucked, but what do you do, its a great cab.
     
  8. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    It is possible that a maggot did get into narrow slot that the former and coil move back and forth in. It would have to be cleaned out. Chances are it is something else. More than one speaker being afflicted with such a rare problem is a bit odd. Although maggots do like cheese and if the other guy was playing some cheesy stuff, you never know.

    Below is a cut away section of a speaker. Below that is an illustrated diagram showing the various parts that make up the speaker. As you can see space is tight in the air gap. Any misalignment can result in impeding the movement of the coil -former-cone assembly.

    If you tested the speaker by itself, disconnect from the wiring harness, with an ohm meter, you can tell if the coil is blown. Sometimes when it does this, the coil wires can get jammed in the air gap and lock the cone in place.



    [​IMG]

    [​IMG]


     
  9. I'm with Mr. Foxen. Sell the working ones and buy some b810s. You won't be dissapointed. Or just replace the bad ones with b810s
     
  10. I had a box that was dropped in transit. The packaging came loose and cab copped it. Speaker coil shifted and was toast.

    It's possible the cab may have been dropped or kicked over.
     

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