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Question - crossover circuit

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  • Question - crossover circuit

    I’ve created a speaker with a 4 ohm woofer (side firing), an 8 ohm full range driver, and a rear facing 8 ohm tweeter. To maintain a overall impedance of 8 ohms, I was going to have the full range and tweeter in parallel and then in series with the woofer which comes to 8 ohms. I am keeping it simple using a first order high pass circuit for the full range (600 Hz) and tweeter (6500 Hz) and letting the woofer be full range. My initial circuit ended up applying a high pass to the woofer which was not good. One option would be to run them all in parallel but that would bring the impedance down to 2 ohms which is too low for my amp to drive. Can I add a 2 ohm resistor to the drivers running in parallel to bring the impedance up to 4 ohms? Any issues with that? Or what would be the proper circuit for my original series parallel configuration?

  • #2
    I'm sorry, but this will not work, even with first order filters.

    1- do not add resistance to compensate for impedance, as it messes with woofer box alignment, and burns off power as heat. This can be a fire hazard on woofers.
    2- the impedance does not work like you think it does with a xover in place. With a conventional 1st order parallel network xover as you suggest, the impedance of the drivers will rise in the stop-band and be the same in operational bandwidth. This means the higher impedance rises cancel out to form a system impedance of the respective drivers in their own ranges, and not paralleled directly.
    3- if you highpass or lowpass anything in series wired connections as you intend, everything in the chain will be high or low passed. So- if you wire as you intend, the highpass of the tweeter and bandpass of the full-range is all the woofer will see. Bass will not get to the woofer at all.
    4- Since xovers are as I have laid out above, a 4 ohm woofer will yield a 4 ohm impedance in the bandwidth of the woofer in a properly xovered, designed, and wired system.

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    • #3
      You're thinking of them like resistors, which they are definitely not.

      The crossover circuit will keep them from being in parallel at the same frequencies, leaving you with a minimum of 4 ohms for the low frequency range where the woofer lives. Never put a series resistor in with the woofer, that's just a waste of power and at worst a fire hazard.
      Electronics engineer, woofer enthusiast, and musician.
      Wogg Music
      Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus


      • #4
        Yes, I have been thinking of the speakers as resistors (pretty new to this) so thank you for clarifying that. Any suggestions on how to properly design the circuit?


        • #5
          That's the sound of a massive can of worms opening

          Short version... All parallel, cap in series with full ranger, another cap in series with tweeter. Values TBD based on their impedance, not going to guestimate for you myself. That will make noise, but may suck.

          Long version... read up some of the resources in the building bible sticky thread, get Speaker Building 201 book, come back with lots of more specific questions...
          Electronics engineer, woofer enthusiast, and musician.
          Wogg Music
          Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus


          • #6
            I switched my circuit to all parallel and that worked.

            thanks again


            • #7
              Side-firing woofers are only good below maybe 100Hz, otherwise you're projecting the midrange out sideways. That's like sitting down in front of two stereo speakers, but turning the speakers at a right angle (sideways) to you. Bad idea.
              The rearfiring tweeter is for what?

              What, exactly, are you trying to do?


              • #8
                Originally posted by Chris Roemer View Post
                Side-firing woofers are only good below maybe 100Hz, ...
                Chris, not to confuse the op or get too far off topic, but I thought side firing woofers were good up to ~200hz, possibly even close to 300 if crossed quickly enough?



                • #9
                  OK. Still, his 600Hz would not sound good to me.

                  W/all 3 drivers in a parallel (standard) arrangement:
                  You'll have freqs > 10kHz coming from all drivers unattenuated, firing in 3 diff. directions, a real phase mess, and a real mess in general.

                  From about 10k down to 1k or so, while the tweeter is rolling off, both the woofer and FR will be playing, in 2 diff. directions, with phase issues.

                  Below 1000Hz the FR WILL begin a rolloff, but its output will rise again (prob. to full output?) around its "in-box" resonant freq. (near its Fs?). In my example this was at 60Hz.

                  The rear-firing tweeter is for what, again?