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Thread: Diaphragm diameter and high frequency response.

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  1. #1
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    Diaphragm diameter and high frequency response.

    Dear Sirs,

    I have a technical curiosity.
    From this forum I understand that JBL's new 476Be has extension up to 40kHz
    An exceptional achievement for a driver with a 4" diaphragm.
    For instance the also wonderful old jbl 375 should have a much more limited high frequency response.
    My question is: what could be the main reasons of such an exceptional high frequency performance for the 476Be ?
    A lighter diaphragm? a much more powerful magnet ?

    Thank you very much indeed.
    Kind regards,

    beppe

  2. #2
    Maron Horonzakz
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    Several things come to mind 375 v 476... diamond pattern surround and Be phrams,, Phase plug redesigned (coherent phase plug) some EQ in xover....The 476 doesnt do much above 20K the super tweeter carries on from there.

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    Senior Member Hoerninger's Avatar
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    In addition to the previous answer, the high frequency limit depends on
    - driver moving mass
    - driver voice coil inductance and
    - front cavity compliance.

    In a real world horn design, the composite high frequency rolloff is a complex combination of all three corner frequencies taken together.
    More details can be found here:
    http://www.xlrtechs.com/dbkeele.com/...TS%20Paras.pdf
    _________
    Peter

  4. #4
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by beppe61 View Post
    Dear Sirs,

    I have a technical curiosity.
    From this forum I understand that JBL's new 476Be has extension up to 40kHz
    Citation please; I'm not seeing that in the specs anywhere....

  5. #5
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    Quote Originally Posted by beppe61 View Post
    My question is: what could be the main reasons of such an exceptional high frequency performance for the 476Be ?
    From various conversations I gathered that the extended response to 40 kHz was kind of a surprise to everyone. Evidently the dip around 20 kHz is temporary. You might want to send Steve Schell a PM.
    Quote Originally Posted by Maron Horonzakz View Post
    The 476 doesnt do much above 20K the super tweeter carries on from there.
    We were informed that the 476Be was allowed to run full out despite what the published voltage drive curve might indicate. I think if one runs the network through spice that will be revealed but I could be wrong. It's been a few years since I examined the whole thing. The super tweeter is a technical requirement for the originally intended marketplace.

  6. #6
    Senior Member grumpy's Avatar
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    this is what I got when I ran it some time ago... -grumpy
    (10Hz - 100KHz)
    Attached Images Attached Images  

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    That looks familiar, thanks grumpy.

  8. #8
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    Quote Originally Posted by grumpy View Post
    this is what I got when I ran it some time ago... -grumpy
    (10Hz - 100KHz)
    Man, once that thing gets going, it's pedal to the metal. (That's too weak, see below.)

    Grumpy, have you done the 045Be?

    (Thanks to Ed "Bid Daddy" Roth.)
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  9. #9
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    476Be to 40Khz

    Quote Originally Posted by beppe61
    My question is: what could be the main reasons of such an exceptional high frequency performance for the 476Be ?
    A lighter diaphragm? a much more powerful magnet ?

    - Everything mentioned so far contributes , as well as ;

    - I believe that some of the credit ( for the response extension ) needs to be given to JBLs' newer gap topologies ( of course, I'll readily admit that I don't actually know if JBL implemented the design principles of this patent into the 476Be or 2452 drivers - merely a guess ) .

    - A close read of JBLs' 1991PATENT # 5117462 will show what I'm geting at .
    - Venting the voice-coil & the domes' surround into the phase plug, has very tangeable benefits ( so says the pdf ) .

    <>

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