High efficiency 95dB/2.83V, 3-way, 1st order series crossover.

Discussion in 'Speakers' started by murphythecat, Jun 9, 2022.

  1. murphythecat

    murphythecat GRU-powered uniformed trumpkin

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    I began this project around 2012 armed with a mini dsp, 12" woofers in a 125L cabs using the pr170mo along the PR17 supertweeter xo'ed at 5khz. Passive xo between the mids-tweet and active woofers via mini dsp. It sounded great but i could never make the bass sing along the mid and treble.
    2012:
    [​IMG]
    2022:
    [​IMG]

    About a year ago, i had way too much time on my hands and so this project came back to life!

    A friend that used to be active at DIYA and is an "Audio Industry" personality who prefers to named as "Magnum Innominandum" helped me greatly to design this speaker. He helped to design the cross over and the entire system really. I'll quote some of his comments about the design.

    Drivers:
    Planar tweeter: HiVi RT2HA: https://www.parts-express.com/HiVi-RT2H-A-Planar-Isodynamic-Tweeter-297-407
    Midrange: Audax 170MO: https://www.madisoundspeakerstore.com/pro-sound/audax-pr170m0-6.5-midrange-100db/
    Woofers: Eminence Omega Pro 15's https://usspeaker.com/OmegaPro-15A-1.htm

    Measurements:
    FR measurements: Yellow line is 1.5M away from the speakers, mic at the mid level. the green line is the same speaker but now measured from the listening position.
    [​IMG]

    Series xo:
    The whole crossover contain no resistors to lower sensitvity, only two Inductors and two Capacitors.
    The reason I always prefer series networks for 1st order crossovers, is that due the use of "shunt elements" at frequencies where the driver impedance is approximately resistive means the drivers inductance and LF resonances do not require compensation networks.
    This is totally independent from all the articles all over the net where debunkers try to prove that there is no difference between series and parallel network. This case is only true for resistors, not for real drivers. A parallel type crossover would require both voice coil inductance and driver LF resonance to be compensated, making the parts count very large, especially for the midrange.
    In effect, the planar Tweeter is a resistor, the midrange will need RC "Zobel" to compensate the voice coil inductance and at least one RLC "Trap" to compensate the impedance "humps" at low frequencies to make it behave like a resistor. The Bass Driver would need a RC "Zobel". Then an equivalent parallel crossover will work broadly equal. The series network does not need these compensation elements and is super simple.


    Midband sensitivity is around 95dB/2.83V/1m with around 6 Ohm impedance.

    final crossover pics. MIT multi cap PPFX caps used in the critical midrange. MKP type caps for the bass.
    [​IMG]

    Mid-tweet offset:
    normally, a offset of the mid-tweet in relation to the woofer result in a smoother transition between bass to mid. I would have prefered to have the woofer, the mid and the planar all centered but here's the simulations:
    no offset:
    [​IMG]
    offset:
    [​IMG]

    Sub enclosure for the mid:
    closed enclosure to isolate the mid-tweet. of course, theres a back panel that come and seal the sub-enclosure haha
    [​IMG]
    Denim foam installed:
    [​IMG]

    Bracing is based on this super simple design: http://www.realoldiesradio.com/docs/EV/ElectroVoice_TL606.pdf
    ive installed on each inner panels 2x4 glued. i havent taken any pics of the bracing. ive really went the simpler and probably compromised bracing technique by gluing 2 x4 along the back and side walls, but I hear absolutely no cabinet colorations to the sound.


    Here you can see the FR when the mid have been removed. interesting to note here that the sub enclosure was not closed, hence you see a peak at around 600-800hz. that peak is gone in the final speakers once the sub enclosure is closed and foam installed. mic at the LP
    [​IMG]
    only thing left is to have my ports being cut to the right lenght and install them. not sure if my neighbor will appreciated the added extension boost :)
     
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    Last edited: Jun 12, 2022
  2. Cspirou

    Cspirou They call me Sparky

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    Did you really get a PCB made for a one-off build?
     
  3. 9suns

    9suns [insert unearned title here]

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    Epic build! Loved the crossover choice, very intelligent thinking and execution, the less the better and there's nothing better than picking the right kind of speaker (high sensitivity, big 3 way) and drivers that don't need to be padded because they already are all of similar sensitivity and so well behaved that can be used with 1st order filters.

    Congratulations, only good things come out of being passionate, smart and dilligent!
     
  4. murphythecat

    murphythecat GRU-powered uniformed trumpkin

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    thanks
    that project meant a lot to me and hundreds of hours went into its planning! im glad to report it sounds MUCH better then it looks :)
     
  5. murphythecat

    murphythecat GRU-powered uniformed trumpkin

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    the green board? its just some old re-used board.
    the final board is a empty board without any traces
     
  6. purr1n

    purr1n Desire for betterer is endless.

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    Very cool. I've always wanted to do a series xover. Definitely the right drivers here for such with 1st order. Did you do a straight series xover or do a cascade on the tweeter or woofer part?
     
  7. purr1n

    purr1n Desire for betterer is endless.

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    https://www.tubecad.com/2017/11/blog0403.htm

    Try cascading the woofe too. Omega 15 Pro extends pretty good, keep slow woofer from infecting the mids/highs. Would be curious what sounds better. Unless priority is to keep tweeter from exploding, but I suspect the HiVi is more robust than what specs say.
     
  8. uncola

    uncola Friend

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    Love seeing these big woofer sensitive designs…. Did you never name your speaker design? Something suitably hubristic like Charlemanes or Musashi’s?
     
  9. 9suns

    9suns [insert unearned title here]

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    https://www.tubecad.com/2019/08/blog0473.htm
    This one is also an amazing idea (the one that says "Now for Something Altogether New"). Would be a great experiment and you can always go back to your current crossover configuration if it is not to your liking.

    But yeah I understand that your speakers must sound amazing, it's hard to screw it up when you choose the big, well behaved drivers, high sensitivity and simple crossovers path IMO.
     

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