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Thread: Is my 2123 h out of specs ?

  1. #1
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    Is my 2123 h out of specs ?

    Hello,
    i recently bought a pair of old 2123H and i'm a little bit disappointed. i measured them and the result is not very good, and does not match at all the JBL data.
    Are JBL's published curves totally false or is my driver to be reconed .
    A jpeg of the 2 responses is attached
    Jean
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  2. #2
    Senior Member jcrobso's Avatar
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    There could be some difference in measurement methods.

    JBL measures the speakers in an anaphoric chamber where there are NO room reflections.
    To get the same results you have to duplicate the room as well.

  3. #3
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    Quote Originally Posted by jf65 View Post
    Are JBL's published curves totally false or is my driver to be reconed .
    Jean
    JBLs' published curves for the 2123 are quite a piece of fiction .

    - Mind you, they are plus or minus 2 db / with a ton of smoothing applied no doubt .



    Yours look to be about right ( with some explanations in order ).


    (i) The wide notch at 150 HZ is most likely a result of measuring conditions ( ie; diffraction from the baffle board or out of phase cancellations caused by floor/wall bounce to the test mike ) .

    (ii) The medium-wide notch at 290 HZ ; ditto to the above explanations .

    (iii) The notch at 1400 hz could be real / hard to say without more info about your testing procedures .

    (iv) That broad peak between 400 & 1K is quite real .


    I'd suggest retesting your drivers after mounting them ( one at a time ) on a very large open baffle with the driver position offset asymmetrically from the edges of the board .

    This will help smooth out diffraction/cancellation effects . Close miking ( .25" to .5" ) the cone also helps .

    So far I don't see any real good reason to recone ( plus, recone kits may not be available or even affordable ) .

    FWIW ; Bad curves are really easy to create .



    <. cheers

  4. #4
    Administrator Robh3606's Avatar
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    Try what Earl suggests. A close in measurement will give you a better idea. Could be your baffle size or box dimensions are contributing to what you see. That published curve is bogus. I had a similar surprise the first time I measure mine. Don't worry once you get them dialed in they are worth any headaches. Here's what a 2122 look like mounted in a 4344 cabinet

    Rob
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  5. #5
    Senior Member Eaulive's Avatar
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    Yup, what they said, and if you have a big backyard with heavy grass and no big walls around, you could try make the measurements there. It's still far from an anechoic chamber but certainly better than your living room

  6. #6
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    Hello,
    your posts reassure me and i will measure them in the garden next week (we have random showers these days), in their boxes an i will try an open baffle.
    I wanted to put them between an Altec 416 and a 2445 on an Iwata horn which are crossed at 600Hz, filling the space between 300 an 1000/1200, but they seem to have more energy around 600/800, which is not really what i expected to help the boomer above 300. I believe the 2445/Iwata can go down to 600 more easily than the 416 go up to 600.
    Best regards,
    Jean

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