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Thread: What's with the Aluminum Cap?

  1. #1
    Senior Member Baron030's Avatar
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    What's with the Aluminum Cap?

    Here is a question that I have been meaning to ask for about a year now.
    When I purchased a pair of 2012H drivers, they came with an aluminum cap mounted on the back of the magnet.

    Does anyone have any ideas as to it purpose?

    Thanks,
    Baron030
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  2. #2
    Webmaster Don McRitchie's Avatar
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    I'm not sure what to look for. All that I see is the cast iron back plate that has the JBL logo, vent hole and horizontal striations cast into it. This is an integral part of the magnetic return structure, and part of every ferrite magnet motor.
    Regards

    Don McRitchie

  3. #3
    Senior Member alskinner's Avatar
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    It is aluminum and held to the ferrite magnet structure by glue. When I bought mine they fell off during shipment, not sure if it is purely decorative or part of the acoustic structure.


    Regards

    AL

  4. #4
    Senior Member edgewound's Avatar
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    Quote Originally Posted by Baron030
    Here is a question that I have been meaning to ask for about a year now.
    When I purchased a pair of 2012H drivers, they came with an aluminum cap mounted on the back of the magnet.

    Does anyone have any ideas as to it purpose?

    Thanks,
    Baron030
    The 2012H is a midrange/midbass driver in the VS2210,VS3215, VS3218 system. The aluminum cover you're referring to is probably the back loading chamber for this horn loaded 10". Maybe yours came from a parted out system?

    Your picture just shows the raw frame 2012H back plate...which is typical for that driver.
    Edgewound...JBL Pro Authorized...since 1988
    Upland Loudspeaker Service, Upland, CA

  5. #5
    Senior Member alskinner's Avatar
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    US Speaker sells the raw 2012h for about 249.00. Besides the VS series. it is also a great midbass for a DIY 4 way system.

    AL

  6. #6
    Senior Member Guido's Avatar
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    Quote Originally Posted by edgewound
    Your picture just shows the raw frame 2012H back plate...which is typical for that driver.
    I owned 2 2012 speakers. One had this "backcap" the other not.
    The backcap is just cosmetical. It's no part of the magnetic structure

    Can't find the pics
    BLS Reference on Passlabs XA 30.5 + Everest DD66000 clone on Pass XA 100.5

  7. #7
    Senior Member Don Mascali's Avatar
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    I think you are refering to the model/serial number plate on units sold as individual drivers. On drivers that need it there is a vent in the center of the plate, others are completely covered. They serve no purpose other than ID. OEM drivers and units sold to other manufacturers are sold naked and usually without the rubber donut over the exposed magnet that prevents chipping. Usually the model # has a PL (ie. 2226 HPL). I read it as H= 8 ohm and the PL as private label but that info is worth what you paid for it I really don't know.
    4406, 4412A, L100, L100t3 (3 pair), L1, L7, 4645C, 4660A, 4695B, SR4735 and various DIY JBL Pro loaded systems.

  8. #8
    Senior Member Baron030's Avatar
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    Thanks everyone for all your feedback.
    When I purchased these drivers from US speaker about a year ago, my first thought, when I opened the boxes was that they were magnetically shielded.
    But, a quick test with a screw driver proved that was not the case.
    Then, I thought that maybe the aluminum caps had something to do with the magnet's circuit. But, that really does not appear to be the case.
    So, the aluminum caps really are just cosmetic.

    Thanks, Mystery Solved.
    Baron030

  9. #9
    Senior Member edgewound's Avatar
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    Quote Originally Posted by Baron030
    Thanks everyone for all your feedback.
    When I purchased these drivers from US speaker about a year ago, my first thought, when I opened the boxes was that they were magnetically shielded.
    But, a quick test with a screw driver proved that was not the case.
    Then, I thought that maybe the aluminum caps had something to do with the magnet's circuit. But, that really does not appear to be the case.
    So, the aluminum caps really are just cosmetic.

    Thanks, Mystery Solved.
    Baron030
    I'd really love to see a photo of that aluminum cap. I'm having a hard time believing that it's just cosmetic....why would JBL want to cover that beautifully cast motor structure?

    If it reaches all the way to the speaker frame mounting flange and covers the cone, then it's purpose is to be an acoustic loading chamber for midrange isolation.

    Can you post a pic? I'm Reeeaaallyy curious....
    Thanks Baron.
    Edgewound...JBL Pro Authorized...since 1988
    Upland Loudspeaker Service, Upland, CA

  10. #10
    Senior Member Baron030's Avatar
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    Hi Edgewound
    I'm sorry; I didn't include a better picture. But, the speaker cone is visible in the photo.
    Since, the driver is now installed. (See my DIY Forum posts for details.)
    It really would be kind of a pain to take it out and photographic again.
    So, I have cropped, lighten and added a red arrow pointing to the speaker cone.
    If I had included a side view, it would have shown that aluminum cap only covers the magnet.
    The aluminum cap does not cover the 1/2" thick top plate on this driver.
    And there is at least an inch wide gap for air to flow between the top plate and the front of the frame.
    So, the aluminum cap is not some type of enclosure.
    I know it is really odd for JBL to add an aluminum cap, just for cosmetic reasons.
    That's why I posted this question. It's a real mystery.
    Baron030
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