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Thread: JBL 2440 off-center vc gap.

  1. #1
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    JBL 2440 off-center vc gap.

    Hello! Today trying my 2440 with a pair of 2355 horns i realise that one of the drivers got less dynamics, realism and detail. So i decide to take out the diaphragm to inspect it and clean the vc gap. When i loose all the screws i found that the diaphragm was a little stacked so i pulled it out very carefully. Thankfully the diaphragm and coil are in good condition but watching carefully the phase plug and the vc gap i found that the gap in one side is tide while in the oposite side was wider and that was visible clear. Is there any way to fix that problem? The difference in sound is audible but not that tragic although im a little perfectionist with my system so..... :/ regards!

  2. #2
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    Does this work?? Any more infos about this solution??

    ""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)""

  3. #3
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    Hi,

    Your quote is from LHF member "subwoof" ( if I remember correctly ).

    If he says it works >> then it works!



  4. #4
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    Quote Originally Posted by Earl K View Post
    Hi,

    Your quote is from LHF member "subwoof" ( if I remember correctly ).

    If he says it works >> then it works!


    I will try it tomorrow morning. I hope it will work!

  5. #5
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    Well this solution doesn't seem to work. I try to fix the top plate with the bolts on place but cant be moved like this. I remove the bolts and hit the plate again . The plate moves but after that you cant screw in some bolts. It looks like the plate is in the correct place and the phase plug is off center. Can this thing happen? Regards

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    And some photos
    Attached Images Attached Images     

  7. #7
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    The idea now is to drill and open a little more the holes of the top plate so it can be moved and screw the bolts easier with the holes wider. Any other ideas??

  8. #8
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    Fixed with a different way

  9. #9
    Member Flamingo's Avatar
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    Quote Originally Posted by retro soulman View Post
    Fixed with a different way
    Pray, do tell

  10. #10
    Senior Member Flodstroem's Avatar
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    I have had the same problem with of center of the center pole (2440). I had to demag it and open it. I found out that there was a center ring of alu that normally holds the center pole in place. It was bolted to the inside of the top plate if I remember it correct. The centering ring had been moved, not much but a few tens of a millimeter After correcting it and put all pieces in place I could remag it and then it was OK.........
    Flodstroem

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