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Thread: DingDing goes DIY: JBL 2404 mounted inside or outside 2360A and one or two 2123?

  1. #31
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    Thank you for the pictures. Do you like the result?

    I will build that bracket to have 2404 mounted just below the mouth and in the same plane as 2360. Then delay 2404 to account for the distance between 2446 and 2404. Will post pictures of the bracket and may 3D model it if you're interested. What concerns me about having them behind the mouth is that a lot of the frequencies will be bounced off the rare of the 2360.

  2. #32
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    Very interesting thread

  3. #33
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    Quote Originally Posted by DingDing View Post
    Quick questions regarding distance from 2123 to 2226.

    Assuming 343m/s speed of sound, and xo @ 400 hz => wavelength = 343/400 = 0.8575m.

    It has to be within 1/4 the wavelength to connect acoustically, right? So that would be 21.5 cm from the acoustic centers of the drivers. That's fairly close.

    Does it need to be 21.5cm from both drivers, or the average distance between them in relation to 2123? Can make a drawing if that question is unclear.

    Is it correct to use the XO point as a basis for calculating maximum distance between drivers? As the drivers overlap after the xo the distance will obviously change with frequency and can and will create lobing, right?

    Can delay in the digital domain do anything to this particular problem within some constraint? Two drivers 10m apart can't sound like one driver no matter how much delay (if you're in the middle) obviously, but if we're talking about 10-20cm off from the maximum distance, will it work well?
    Long time ago but basically yes but its not overly critical

    Dispersion match at the crossover point has more impact than critical spacing.

    The horn will nearly always loose pattern control at the low end.

    So if its an 80 degree horn it might flare out to 100 near the bottom end. That can help if the driver load and distortion is not rising.

    Use -6 db as the reference for the dispersion

    In fact you can compromise other things by trying too hard on clustering drivers like diffraction and early reflections.

    I could not get the 2344A close to the 2123 without reflections.

    An easy but relative precise way of determining absolute phase (and lobes) in the crossover region is to reverse the phase on one driver once you have the slopes set up.

    Unless you're using DSP filters there is going to be phase shift and delay in the low pass filter and phase shift delay around the low end of the horn.

    So the voice coil centres are not likely to be the reference for absolute phase.

    With an analyser measure the notch at the crossover and gradually move the voice coil centres until you get an even deep notch at your reference point (the mic position).

    The move the mic in the vertical plane to work out the lobes.

    LR 24 db filters really shine in terms of minimal lobes.

    Its not possible without an optimiser like LEAP for passive networks but you can shoot for 36 db slopes in digital with DSP and the lobes are significantly reduced around crossover point (ref M2)

    Is it important? Only if your horn has wide vertical dispersion in the proposed crossover point .

    With a narrow vertical dispersion on the horn this can actual help minimise vertical lobes

    Check out Pi Loudspeakers white papers if you are interested in the topic.

    Wayne is helpful and a nice guy.

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