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Thread: Question: Re: Re-foaming drivers

  1. #1
    Senior Member LE15-Thumper's Avatar
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    Question: Re: Re-foaming drivers

    Ok, I have seen all the posts (Most) on refoaming and using the 30hz tone method without cutting dustcaps.
    One question that is driving me nuts, and keeping me from trying this method. If you are a applying a 30Hz test tone to the driver WHILE the glue is drying. What keeps the foam from lifting off the edge of the basket ? Wouldn't the up/down motion of the cone lift the foam off the basket if the glue is not yet dry ?
    What am I missing ??
    LE15-Thumper
    "Give me JBL, or give me death"

  2. #2
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    You aren't supposed to drive it hard enough to cause the foam to separate from the basket flange. Get a driver, apply some 30 Hz tone to it and note the movement of the surround.

    What am I missing ??

    Your missing the experience of just doing it. All will become clear.

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    Administrator Robh3606's Avatar
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    The glue gets very tacky and if you look there is not that much movement where it actually is glued. You are not running them at X-Max like Giskard says when you do it, it will become clear. I have used this method several times and it has worked very well.

    Rob

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    Senior Member LE15-Thumper's Avatar
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    What causes the self centering action ?

    BTW...A-La David Carradine, "I am very greatful, you have taught a young grasshopper well."
    LE15-Thumper
    "Give me JBL, or give me death"

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    Senior Member LE15-Thumper's Avatar
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    Ok, I got some scrap NON-JBL drivers to try out first.
    LE15-Thumper
    "Give me JBL, or give me death"

  6. #6
    Administrator Robh3606's Avatar
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    The flux from the coil and magnet center the coil. What you have to watch is you don't tilt the cone on a long throw driver. Thats why you are running the 30Hz. Not to X-Max but a healthy excursions once it starts to really tack well.

    Rob

  7. #7
    Senior Seņor boputnam's Avatar
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    Quote Originally Posted by Robh3606
    The flux from the coil and magnet center the coil.


    The coil oscilating in the magnetic field is "self-centering", so long as it is not obstructed / prevented from doing so.

    Use a voltage drive of 1 to 3 v (max) - I stick my ear into the cone as I approach the 3v drive to listen very carefully for any "rubbing" or mechanical sounds. If present, while the glue is soft you can gently reposition the cone - but it's like moving your dog, you push on the opposite direction you want it to move...

    Let the glue set at a gentle 1 to 1.5v drive and check every 30-minutes.
    bo

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    And if you use JBL recone glue instead of the supplied glue it will set much faster. I used the supplied glue to attach the foam to the cone because it dries nice and clear and the JBL recone glue to attach the foam to the basket. Still allow the full 24 hours drying time before a power test.

    BTW - I like Rick's 12" kit for 2214H's but not 128H's. I think someone else posted the same thing somewhere.

  9. #9
    Senior Seņor boputnam's Avatar
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    Quote Originally Posted by Giskard
    BTW - I like Rick's 12" kit for 2214H's but not 128H's. I think someone else posted the same thing somewhere.
    Cool. Was it a fit, or pliant issue?

    And, I agree on the glue. The slow setting stuff has saved a lot newbies from "do-overs". And, that it drys clear (and shrinks a bit) makes the handiwork look great...
    bo

    "Indeed, not!!"

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    It was a fit issue. I did the 128H right after the 2214H and it ended in disaster. The foam fit perfectly on the 2214H and it came out great. A bit of care was required for the 128H I suppose and I evidently had none to spare at the moment.

  11. #11
    Administrator Robh3606's Avatar
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    Yeah I did 128h-1 and 2214's and the compliances were different diameters. Even with the correct kit for the smaller diameter 128 you had to watch the centering to the cone very carefully. The compliance roll edge didn't go up flush to the cone like the 2214.

    Rob

  12. #12
    Senior Seņor boputnam's Avatar
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    Quote Originally Posted by Giskard
    It was a fit issue. I did the 128H ... and it ended in disaster.
    Good to know!!

    All this time I thought it was my limited ability or lack of experience...
    bo

    "Indeed, not!!"

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    Quote Originally Posted by boputnam
    Good to know!!

    All this time I thought it was my lack of experience...
    It was Bo. Experience matters. I've not done very many refoams at all.
    I've done countless recones.
    Oh, and I've screwed a few of them up too.
    Quote Originally Posted by Robh3606
    Even with the correct kit for the smaller diameter 128 you had to watch the centering to the cone very carefully. The compliance roll edge didn't go up flush to the cone like the 2214.
    Right. And I simply didn't give it the attention it deserved. It was a trial anyway so I'm not broken up about it at all. The surround was an extra.

  14. #14
    Junior Member Bill Ding's Avatar
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    Quote Originally Posted by boputnam


    The coil oscilating in the magnetic field is "self-centering", so long as it is not obstructed / prevented from doing so.

    Use a voltage drive of 1 to 3 v (max) - I stick my ear into the cone as I approach the 3v drive to listen very carefully for any "rubbing" or mechanical sounds. If present, while the glue is soft you can gently reposition the cone - but it's like moving your dog, you push on the opposite direction you want it to move...

    Let the glue set at a gentle 1 to 1.5v drive and check every 30-minutes.
    I need to refoam a pair of JBL L-50 I recently purchased. Could you explain the source of the 30hz tone? When you refer to the 3v is that from a power supply and if so ac or dc?

    Thanks

    Bill

  15. #15
    Administrator Robh3606's Avatar
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    Depending on who you get your kit from some will supply a cd with a 30Hz tone. Just drop it in the cd player on repeat and your done. It's simple enough to make your own if you have software. Any kind of signal generator, even a computer sound card will work just fine.

    Rob

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