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Thread: JBL 4365 Active Crossover settings

  1. #241
    Senior Member Ed Zeppeli's Avatar
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    Thanks for this thread.

    I would appreciate if, in a nutshell, it could be explained to me how to replicate a given voltage drive plot via DSP. I am using the dbx venu360 and would like to get as close as possible to the given curve using what I have at hand.

    Is it all done within the HF/LP settings of the crossover or are there also eq points to consider?

    Thanks much,

    Warren
    DIY Array, 2242 sub, 4408, 4208, Control 8SR, E120 Guitar cab, Control 1, LSR305.

  2. #242
    Senior Member grumpy's Avatar
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    Almost always both. I don't have a specific recipe for you though.

    It really helps to have a way to measure the output of the crossover/EQ
    though (often the plots pictured in a DSP setting GUI are not of
    sufficient resolution or don't show the crossover and EQ functions summed).

    I'd start with crossovers that were close to the target voltage drive curves
    and try fairly low Q (not narrow band) corrections where needed, and avoid
    large gains/cuts. Compression driver + horn eq being possible exceptions
    (e.g., constant directivity horns have an expected correction)

  3. #243
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    Quote Originally Posted by Ed Zeppeli View Post
    Thanks for this thread.

    I would appreciate if, in a nutshell, it could be explained to me how to replicate a given voltage drive plot via DSP. I am using the dbx venu360 and would like to get as close as possible to the given curve using what I have at hand.

    Is it all done within the HF/LP settings of the crossover or are there also eq points to consider?

    Thanks much,

    Warren
    A voltage drive plot calculated with constant loads (e.g. 8 Ohms resistors) won't help you much to get started. You should have the real drivers in place and should measure the effective voltage at the driver terminals.

    I don't know the dbx venue 360. The Behringer DEQ 2496 can help you to find an equalizing curve in a few minutes. Maybe dbx can do something similar, no idea. The Behringer doesn't cost a fortune.

    Ruediger

  4. #244
    Senior Member Ed Zeppeli's Avatar
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    Quote Originally Posted by grumpy View Post

    It really helps to have a way to measure the output of the crossover/EQ
    though (often the plots pictured in a DSP setting GUI are not of
    sufficient resolution or don't show the crossover and EQ functions summed).

    I'd start with crossovers that were close to the target voltage drive curves
    and try fairly low Q (not narrow band) corrections where needed, and avoid
    large gains/cuts. Compression driver + horn eq being possible exceptions
    (e.g., constant directivity horns have an expected correction)
    Thanks grumpy. So I can create the general slopes with the hi and low pass filters but then I add the dips and moguls via EQ used as broadly as possible. This is making more sense to me now.

    So, having a way to verify these tweaks electrically and not acoustically is truly the only way to confirm that I have duplicated the voltage drives as intended by the designer. It would be a helluva lot of work with a multimeter and sine waves.

    Quote Originally Posted by Ruediger View Post
    A voltage drive plot calculated with constant loads (e.g. 8 Ohms resistors) won't help you much to get started. You should have the real drivers in place and should measure the effective voltage at the driver terminals.

    I don't know the dbx venue 360. The Behringer DEQ 2496 can help you to find an equalizing curve in a few minutes. Maybe dbx can do something similar, no idea. The Behringer doesn't cost a fortune.

    Ruediger
    Yes, I have the drivers in place and am now just seeing how close my crossover is to the designer's. I have lots of capabilities to get things relatively flat within the dbx and REW but is flat the only concern here?



    This is what I'm trying to replicate.

    Name:  1400 Array Voltage_Response.JPG
Views: 921
Size:  159.1 KB

    I've hunted through various posts and literature and discovered that Mr. Timbers used a linkwitz crossover centred at 750hz. There appears to be a 24db/octave drop on the woofer but there is a much gentler slope on the horn module. It looks to be about 6db/octave. I should definitely be playing with that slope within the venu360 as I had just done both with a 24db/octave and then tweaked things to flat with various parametrics.

    Also to throw a wrench into the works is the fact that I'm using a 2234 woofer as opposed to the LE14H-3.

    Thanks for the information.

    Warren
    DIY Array, 2242 sub, 4408, 4208, Control 8SR, E120 Guitar cab, Control 1, LSR305.

  5. #245
    Senior Member grumpy's Avatar
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    Also, keep in mind that some of these kindly supplied system bi-amp voltage-drive curves assume that the passive HF crossover elements in the cabinets remain in-circuit. In this case, additional rolloff and eq. With the driver horn acoustic rolloff also contributing to the final HF output curve. Guessing the result would give a rolloff complementary to the LF.

    I haven't looked at it hard, but you might also approximate the LF, dual-knee curve with two series Low-pass crossovers (set for different frequencies) e.g. one 6dB and one 18.

  6. #246
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    <<<SNIP>>>Yes, I have the drivers in place and am now just seeing how close my crossover is to the designer's. I have lots of capabilities to get things relatively flat within the dbx and REW but is flat the only concern here?
    It's actually quite simplistic to run a line level (REW) signal into your dbx unit and then back to REW for study.

    That will allow you to see what your finagled & finessed curves look like.

    If you get hip to using a graph tracer ( & then saving the traced results to either a .txt or .frd file ) you can import your target curve into REW ( eg; the one you just posted ).

    Then you can overlay ( within REW ) your measured dbx filter efforts over your target curve ( to see how you are doing ).



    PS; Apparently this tracer is quite good.

  7. #247
    Senior Member Ed Zeppeli's Avatar
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    Cool info Earl. Thanks. That will be very useful.
    DIY Array, 2242 sub, 4408, 4208, Control 8SR, E120 Guitar cab, Control 1, LSR305.

  8. #248
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    Hi Warren

    The 24 db slope is the final acoustic slope.

    However the final tuning of the filter slope will require you reverse the phase of the horn and adjust the anti phase notch in the response manually for the deepest uniform notch at the design point ie on axis with the horn.

    Attempting to adjust the filter while the drivers are in phase will not result in the drivers being in phase at the crossover point. Ie it won't perform correctly.

    There are references to this by respected people on the internet.

  9. #249
    Senior Member Ed Zeppeli's Avatar
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    Had some time today.

    It looks like I may be fighting the internal SAM1HF crossover in my attempts to get a gentler slope. Though I have yet to measure the electrical output of the dbx as per Earl K's suggestion I did import the voltage curve using the trace program.

    Measured from 1 metre. Blue Line is LW24db/octave high pass at 750 hz and Green line is LW12db/octave at 1.82khz. As you can see, both dbx crossover settings result in a steep drop at around 600Hz which I can only attribute to the internal SAM network. The purple curve is the imported voltage drive.

    Name:  VoltageDrive&Acstslope.jpg
Views: 908
Size:  60.8 KB

    So, either I dig in hard and modify the low pass of the internal SAM network, live with the system as is and just tune the crossover and room (which I've been quite happy with so far) or go ahead and purchase the HF section of the 1400 Array networks from Synthesis. Last I checked these were in stock for around $95 each.

    I suppose there is also the charge coupled option as well which is fairly well-documented here.



    Having fun experimenting, so it's all good here!
    DIY Array, 2242 sub, 4408, 4208, Control 8SR, E120 Guitar cab, Control 1, LSR305.

  10. #250
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    Came across the JBL voltage drive jig sheet

    http://www.jblproservice.com/pdf/Net...%20Fixture.pdf

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