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Thread: Going to active xover

  1. #16
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    Barry,

    I did see them. Actually, I've been to most of the threads I could find on the subject. I was looking to see who was getting the best results and how they were doing it.

    I think Ian has a point about the listening position. Where the drivers are stacked vertically and aligned, moving around the components probably doesn't have an effect on the alignment. However, if the drivers are not vertical (stacked from bottom to top and centered) moving from one point to another could alter the result. It would depend on the baffle configuation. As to listening height, there would be some change from sitting to standing, that's probably going to have a more subtle effect, depending on how close you are to the drivers. An alignment issue would be present, but more difficult to pick out during a musical composition. Its really about what you can hear. That's going to be unique to each individual.

    Maxserg, I'll being watching to see how you get along with this.

  2. #17
    Senior Member Ian Mackenzie's Avatar
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    Sorry my explanation may not have been clear.

    If the drivers are stacked vertically the crossover region is not effected moving in the horizontal plane if dispersion is linear in the region.

    However when stacked vertically the crossover region sums like a lobe. The lobe shape depends on several factors - dispersion of the horn and woofer @ crossover point, the order of the crossover slope and so on. The steeper the slope the less interference. There can be several lobes at different angles.

    So ideally the design point should be the listening height.
    The Jbl 4430/4435 brochure has graphic representation of this.

    If the position is moved up or down it can have a significant impact on either a dip or peak in the crossover region.

    When Drivers are not time aligned summing flat at the crossover point can be compromised.

  3. #18
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    Ian, that was pretty clear!

    I noticed a good graphic put up by Frank23 in an earlier thread. Here it is:

    http://www.audioheritage.org/vbullet...-and-2420-2344

  4. #19
    Senior Member Ian Mackenzie's Avatar
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    Great thread

    It’s an interesting problem.

    In my own experience the realities or physical possibilities dictate how much movement can be tolerated.

    For example with a 15 inch woofer you can indent it about 50mm before everything goes to hell.

    The pink noise is a great idea in the absence of test equipment. Trust your ears!

    But like using 2123 is actually a bit tricky.

    The 2123 diffracts with any baffle or horn obstruction like hell in the 600-1200 range due to its wider dispersion.
    You hear it as ghosting. So the best option is to tweak the crossover rather than move the horn forward to get the reverse phase suck out.

    I agree with Mr Widgets comments in that thread.

  5. #20
    Senior Member Ian Mackenzie's Avatar
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    I have attached some images to illustrate the effect of correct summing at the crossover point.

    The first 2 images are vertical polar based on actual measurements at 10 degree intervals.
    Those measurement were then uploaded into LEAP to display polar response curves with the crossover.

    With a bit of screwing around I was able to obtain a uniform reverse phase notch at the design point.

    The left image is out of phase, the second image is in phase.
    The deep notch is the reverse phase at the crossover point (800 hz). The slopes are 36 db per octave so there is not much impact either side of the crossover point whom is what you want in theory.


    The deep nodes are normal either side of the central node and their location will depend on a number of factors.
    My design point was slightly below the centre point.

    The other two curves are out of phase frequency response and in phase. Green is the summed response.

    This is a 2 way design using a 15 inch woofer and a large horn.

    You don't need this precision but its kind of cool to see what happens.
    Getting it right does make a significant difference subjectively. The rules are the same for passive or active crossovers. Ideally you want an adjustable active crossover with independent adjustment of Low and High pass crossover points like the analogue First Watt B4 or a dsp crossover.

    BTW the acoustic centre can be deeper than the woofer voice coil due to the group delay of the low pass filter possibly 0.2 ms or more.

    So if your horn is deeper than the woofer don't stress.
    Attached Images Attached Images     

  6. #21
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    Ian,

    Great images! The verticle images are really interesting, with the green line showing a really smooth response on those 10 degree intervals. Even if it is summed, that's got to sound smooth.

    Awesome!

  7. #22
    Senior Member Ian Mackenzie's Avatar
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    It’s tedious getting it just right.

    I always do reverse phase once the crossover slopes are good.

    Don’t rely on or aim for an in phase smooth response (only)

    If you can swing it buy a measurement device from like Parts Express and start on getting some measurements. It’s not hard and you will doing the real deal as opposed to talking to people about what works in no time

  8. #23
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    4430 active crossover

    Has anyone measured the voltage drives to the 4430 transducers via the passive crossover. I have a pair of 4430's minus crossovers for which I'd like to create an active crossover. The voltage drives to the transducers via the passive network would be a useful starting point .

  9. #24
    Administrator Robh3606's Avatar
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    Take a look here second post. This gives you the woofer curve. The top you are going to have to sim or look for this is a biamp with passive CD comp in place.

    http://www.audioheritage.org/vbullet...ight=4430+5235

    Rob
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  10. #25
    Senior Member Ian Mackenzie's Avatar
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    Further to Rob's post read this and check the RC values for the 4430/4435 cards values
    http://www.jblproservice.com/pdf/Vin...5%20manual.pdf

    NOTE: You will need to build the Horn high pass section of the 3135 networks for to implement the biamp functionality.

    Its not appropriate to attempt creating the horn voltage drive with the EQ.

    You will find the active horn EQ to be too noisy.

  11. #26
    Administrator Robh3606's Avatar
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    Here is the passive voltage drive both systems in JBL Standard test fixture. L pads at max 4435 good as a reference. Courtesy of 4313B

    Rob
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    "I could be arguing in my spare time"

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