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Thread: [How?] Convert passive to active bi-amp speaker

  1. #1
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    [How?] Convert passive to active bi-amp speaker

    Hi everyone,

    How do one convert a JBL 3677 Pro Cinema passive speaker (with built-in crossover network) to active bi-amp mode?
    The reason to do so is to remove the built-in X-curve characteristic of the xo network.

    Is it as simple as this (active bi-amp) ?:
    1 - remove 3677 internal crossover network
    2 - wire up the Crown XLS amp directly to the LF element (woofer) and HF element (compression driver)
    3 - set the Crown to crossover (bi-amp) mode and set a HF crossover frequency to 1.2KHz
    4 - Any bad effects? Any chance of efficiency difference between the woofer and compression driver?

    Did I miss anything?

    Or is there any other crossover network that suits this speaker well without the X-curve?

  2. #2
    Administrator Mr. Widget's Avatar
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    You will need a way to balance the levels between the HF and LF outputs. I'd also put a large NP cap in series with compression driver for protection.


    Widget

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    Quote Originally Posted by Mr. Widget View Post
    You will need a way to balance the levels between the HF and LF outputs. I'd also put a large NP cap in series with compression driver for protection.


    Widget
    The easiest method should be the MiniDSP, isn't it? I've watched the minidsp 2-way video on youtube. How do I know what is the ideal crossover slope (dB/octave) for the woofer and cd? Can one derive these values from the JBL speaker technical PDF drawing/manual? The PDF does show the schematic of the crossover.

    Is there any expert here who know understand the JBL crossover drawing?
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  4. #4
    Senior Member grumpy's Avatar
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    HF part looks like a protective circuit, followed by a 3rd order high pass, a CD-compensation section, and a 1.3 KHz notch filter...

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    Senior Member Mctwins's Avatar
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    Quote Originally Posted by Skylinestar View Post
    Hi everyone,

    How do one convert a JBL 3677 Pro Cinema passive speaker (with built-in crossover network) to active bi-amp mode?
    The reason to do so is to remove the built-in X-curve characteristic of the xo network.

    Is it as simple as this (active bi-amp) ?:
    1 - remove 3677 internal crossover network
    2 - wire up the Crown XLS amp directly to the LF element (woofer) and HF element (compression driver)
    3 - set the Crown to crossover (bi-amp) mode and set a HF crossover frequency to 1.2KHz
    4 - Any bad effects? Any chance of efficiency difference between the woofer and compression driver?

    Did I miss anything?

    Or is there any other crossover network that suits this speaker well without the X-curve?
    Keep the built-in crossover network and connect one XLS(What model??) amp and have fun with it.

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    Quote Originally Posted by Mctwins View Post
    Keep the built-in crossover network and connect one XLS(What model??) amp and have fun with it.
    What's your thought on X-curve in today's cinema sound reproduction?

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    If I were to replace the 3677 built in crossover network, which model is suitable?
    How do I know if it will sound good?

    Here > http://www.eminence.com/pro-audio/hf...ts/crossovers/ < are some models of Eminence xo. Anyone has experience with them? PXB2:800 ?

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    What part in the wiring diagram (post #3) is responsible for the x-curve and would you remove it or bypass it to get more extended response?

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    Quote Originally Posted by boothman View Post
    What part in the wiring diagram (post #3) is responsible for the x-curve and would you remove it or bypass it to get more extended response?
    Hi,

    To check out ( the 3677's HF curve ), I builtup the HF network ( excluding the 1.3K notch filter ) using some spare parts & a JBL 2426H on a RCF 9041 ( this "NLA" constant-directivety horn is only slightly smaller than a 2373 ) .

    For reference, are a few "X-Curves" ( for rooms of different capacity ) .



    To answer your question, there's no one part that one can omit ( or a section to leave-out ) that will help flatten HF response ( generally passive cross-overs don't work that way ) .

    OTOH. one can swap "C4" ( the 2.5 uF cap ) for something larger in value . I used an available 6.8 uF capacitor to get a bit more HF "lift" .

    See the "Blue Line" vs the "Red Line" ( C4 = 6.8uF vs 2.5uF ).
    - The Black Line is the raw response of the horn/driver combo ( though the LF isn't very believable, due to my close measurement distance of 16" )

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    I think the whole HF section might benefit from a complete "do-over" & even that may not work due to the ( overly ) close sensitivities of the woofer & horn/driver combo .

    Bi-amping is definitely the easiest approach ( with some added HF horn-compensation thrown-in ) .


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    Thanks Earl for your work on this. Which part of the schematic is the notch filter? Sorry, new to this. So would removing that and increasing cap value as you suggest improve high frequency response?

  11. #11
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    Hi,

    C5+L2+R7/R8, act together to create the 1330 hz notch filter .



    I'm confident that removing it won't help the HF response issue .
    - It ( the notch filter ) was likely added to smooth out a noticeable "bump" around the 1250hz crossover point ( since I don't have a 3677 , that's just an educated guess ) .

    To move forward, simply strap another cap ( valued between 4 to 6uF ) on top of the existing C4 cap ( 2.5uF ), to see if you get a noticeable increase in HF .


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