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Thread: Is this driver toast?

  1. #1
    Senior Member hatrack71's Avatar
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    Is this driver toast?

    I was listening to this driver and noticed distortion. I am not sure if it is the diaphragm or not as I have not swapped with the other. The gap is not even. Is it toast, ok, or not ok and fixable? should I just get another 2420? Notice the gap is less on the bottom. Name:  IMG_0507.jpg
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    4333As, Valencias

  2. #2
    Senior Member hatrack71's Avatar
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    Anyone? I actually took this driver to someone who repairs speakers after I found it to distort. It had two known issues. A torn screen and boogered up throat into the back side of the phase plug. It was actually the tech who pointed out the uneven gap to me. I honestly didn't think it was bad enough to cause an issue and that is why I was looking for another informed opinion. I guess I could try another diaphragm but am I wasting my time? Not trying to take away from my tech's experience but he admittedly is not an expert on JBL stuff. Could it have come this way from JBL?
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  3. #3
    Senior Member 1audiohack's Avatar
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    I have a 2441 with a slightly uneven gap, I cannot get it to sound good, fair but not good. It shows high distortion on the PWT and low motional impedance indicating the coil or former is in contact with the gap, so it's a paperweight for now.

    I think i read somewhere you could tap the body and move the pole piece but I haven't dared do it for fear of cracking the throat. Hmm, I wonder what Subwoof would do?
    If we knew what the hell we were doing, we wouldn't call it research would we.

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    Senior Member hatrack71's Avatar
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    Quote Originally Posted by 1audiohack View Post
    I have a 2441 with a slightly uneven gap, I cannot get it to sound good, fair but not good. It shows high distortion on the PWT and low motional impedance indicating the coil or former is in contact with the gap, so it's a paperweight for now. I think i read somewhere you could tap the body and move the pole piece but I haven't dared do it for fear of cracking the throat. Hmm, I wonder what Subwoof would do?
    I thought about trying what you are describing but also feared the same outcome or worse. It has obviously been dropped or abused from looking at the outside driver body. Basically, is it cheaper to send this model back to JBL for service or buy another second hand 2420? I am not having good luck at all with used JBL drivers. I got these from an AKer and most of the JBL stuff he gave me in a trade was trashed beyond anything I have seen. I am just trying to salvage anything I can so it is not a total loss. When I was able to sit down and assess the whole lot, I literally cried knowing what I gave for everything. I too wonder what subwoof would do. Thanks Barry.
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  5. #5
    Senior Member 4343's Avatar
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    Cool

    Quote Originally Posted by 1audiohack View Post
    I have a 2441 with a slightly uneven gap, I cannot get it to sound good, fair but not good. It shows high distortion on the PWT and low motional impedance indicating the coil or former is in contact with the gap, so it's a paperweight for now.

    I think i read somewhere you could tap the body and move the pole piece but I haven't dared do it for fear of cracking the throat. Hmm, I wonder what Subwoof would do?
    It's the top plate that needs to be shifted around the pole piece, not the other way 'round. The phase plug and throat are the reference points...
    Mike Scott in SJ, CA
    Drive 'em to the Xmax!

  6. #6
    RE: Member when? subwoof's Avatar
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    subwoof says:

    easy re-alignment guys. have done this many times - even ad-hoc on top of bars before a gig. back in the day when a 2440/2350 fell from the stacks it was SOP.

    What you need are some 8-32 bolts, some WD-40, a dead-drop hammer ( the one with the plastic end filled with shot ) or a decent piece of hardwood.

    you need to make 4 shims - I like to use plastic tops that come with cashew cans and cut them into 1/2 wide strips and keeping the outside tab as a handle. To make the shims thicker ( if needed ) add a SINGLE layer at a time of good quality colored electrical tape ( it's a little stiffer than the black usually )

    BOLT the driver to a small sheet of plywood using the horn mounting bolts so it won't move around on you.

    Put the assembly on a short table / chair or the floor and SIT on it so it doesn't move.

    put a little wd-40 with a q-tip into each of the 4 holes.

    thread in the 4 bolts - some might be hard to thread if the alignment is way off. this will be corrected soon. if one is too hard, wait until the alignment is better.

    put the shim(s) into equal positions around the gap - you probably can only fit 3 due to the off-center, this is ok for now.

    put the side with the larger gap away from you then place a block of wood ( or use the hammer ) and tap on the pole piece toward you.

    the pole piece WILL move and the gap will eventually become even again after a little work. when the gap is even, all the shims will be the same "fit" and all 4 bolts will easily thread in + out.

    When doing all of this remember that the tolerances are very tight and sometimes a given dia will NEVER work correctly in a given magnet assembly. In order to do the alignment it is almost a universal need to slightly enlarge the mounting pin holes with a drill (9/64)

    on your mark, set, go. report progress...


  7. #7
    Senior Member hatrack71's Avatar
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    Damn, you are a genius subwoof. What exactly do you mean by pole piece- phase plug? Wouldn't it make it even wider if I tapped it toward me? Or do you mean tap on the section of the pole piece toward (closest to me) and tap it in a direction away from me? Kinda confused.
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  8. #8
    RE: Member when? subwoof's Avatar
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    parts and pieces

    the pole piece is the flat, round plate that the diaphram mounts to.

    it is held to the return piece ( the iron / painted body ) by magnetism ONLY.

    do NOT mess with the phase plug.

  9. #9
    Senior Member hatrack71's Avatar
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    Crystal clear! Thanks for taking the time to explain it to me. You probably just saved me hundreds!
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  10. #10
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    Check out my thread Refurbishing a pair of 2440, lots of pictures on how they look inside. The 2420 is built the same way, just smaller.

    If there is a speaker repair shop (or a shop with a magnetizer) close by you can demag/align/remag the drivers without any risk. The machine should be for alnico magnets, not for modern ferrite or neodym magnets.

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