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Thread: How high does a 123 A-1 go?

  1. #1
    dig_dabeat
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    Cool How high does a 123 A-1 go?

    I have anice pair of 123A-1's. I did a calculation on them using the WinISD programme, and have put them in some big 7cu ft boxes. Gives the flattest response, with best timing. It is acting pretty much as a fullranger here, and I am experimentiing with adding on midrangers and tweeters. I have tried crossing over some tweeters at around 1K (well 24uF cap) and at higher ponts. (eg 8F cap, and much higher with a very eficient super tweeter. Sound is very nice, but I am wondering if I am missing out on some midrange? Whereddoes the driver start to roll off?
    Hope someone knows!

  2. #2
    Administrator Robh3606's Avatar
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    Take a look at this sheet it will give you an idea of how JBL implimented that driver as a 2 way. Typically they would run it fullrange and have a high pass on the tweeter around 2K. 12db network with the Le-20 or a 6db in the Nova with the LE-25 tweeter. In the L100,4311 they also ran it wide open and just let it roll off.


    Rob
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  3. #3
    Dang. Amateur speakerdave's Avatar
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    123-A Roll-off

    And in the 4311 they started supplementing the mid-range at 1.5k. The issue may not be so much the absolute roll-off as the pattern of dispersion. A twelve inch driver starts beaming somewhere above 1k. If you want the power response field (off-axis response) to be maintained you have to cut in a smaller driver somewhere in there.

    I would guess that JBL's reason for running the woofer full range had less to do with its contribution to the midrange than the desireability of not putting an inductor in front of it; that helped them obtain the tight, punchy bass response and high efficiency.

    David
    Last edited by speakerdave; 10-03-2003 at 08:36 AM.

  4. #4
    Dang. Amateur speakerdave's Avatar
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    Imitation of 604

    Just want to add--there may be more to that inductorless woofer. The oral history says that the 4311's response was tailored to imitate the sound of the Altec 604--the studio standard of the time--and that has a broad bump in the 2k-4k range. The woofer and midrange parallel above 1.5k in the 4311 probably helped with that too.

    David

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