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  • Zobel calculation for woofers in series

    I have 2 woofers wired in series and would like to know if the following calculation for a zobel circuit is correct.

    2x woofers in series.
    Revc - 3.4679 ohms x 2 = 6.9385
    Le - 0.3484 mH (at 1 kHz.) = .6968

    Zobel

    C1= 14473.61302015319 F
    R1= 8.67312 Ohms

  • #2
    Re: Zobel calculation for woofers in series

    Uh, that cap value is a weee bit high. Try 14uF.
    nothing can stop me now

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    • #3
      Re: Zobel calculation for woofers in series

      My calculation is more like 9.3 uF for the cap.
      Dave H

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      • #4
        Re: Zobel calculation for woofers in series

        I used the following calculator for the zobel. Is the reason my calc came out different due to the calculator or does it have to do with the configuration fo the drivers?

        Comment


        • #5
          Re: Zobel calculation for woofers in series

          Originally posted by Hackomatic View Post
          My calculation is more like 9.3 uF for the cap.
          I didn't actually look too close. I just saw the size of that cap and figured it to be a rounding error. But looking at the Le of those drivers, ya, the 9.3uF is probably more correct.
          nothing can stop me now

          Comment


          • #6
            Re: Zobel calculation for woofers in series

            Originally posted by brianpowers27 View Post
            I used the following calculator for the zobel. Is the reason my calc came out different due to the calculator or does it have to do with the configuration fo the drivers?

            Not sure what you used . . I used this one . . .

            http://diyaudioprojects.com/Technical/Speaker-Zobel/
            Dave H

            Comment


            • #7
              Re: Zobel calculation for woofers in series

              I calculate 18.6uf/4.34 Ohms for a single driver. For two in series, reduce C by half and double R.

              Comment


              • #8
                Re: Zobel calculation for woofers in series

                I just realized what I missed. In order to get the 9.2 I needed to multiply the re * 1.25.

                Question: Can individual resistors be added together in series to get the desired resistance? EG: 7.5 + 1.2 = 8.7

                Is the same true for capacitors?

                Comment


                • #9
                  Re: Zobel calculation for woofers in series

                  Resistors placed in series add, but caps should be done in parallel.
                  nothing can stop me now

                  Comment


                  • #10
                    Re: Zobel calculation for woofers in series

                    Originally posted by brianpowers27 View Post
                    I just realized what I missed. In order to get the 9.2 I needed to multiply the re * 1.25.

                    Question: Can individual resistors be added together in series to get the desired resistance? EG: 7.5 + 1.2 = 8.7

                    Is the same true for capacitors?

                    A better way to arrive at Zobel values, is to use the woofers' actual impedance profiles in ANY kind of XO simulator. You can vary the resistor and cap values and "see" how and where the rising impedance gets flattened (even though Zobel component values are not "critical", i.e. - you can vary their values by a large margin and still have a considerable effect on the otherwise continually rising impedance profile).

                    What drivers are you using?

                    Comment


                    • #11
                      Re: Zobel calculation for woofers in series

                      I have 2 polk audio woofers that my friend donated to me. I am working with Jeff Bagby's passive crossover designer for the first time and am not entirely sure what I am doing.

                      I ordered some passive crossover components to design a 3k 4th order LR filter based upon an impedance of 8.35(per the zobel). Does this seem correct?

                      Comment


                      • #12
                        Re: Zobel calculation for woofers in series

                        Whoah! I just modeled the crossover in the PCD. The zobel values it gives for 2 woofers wired in series are dramatically different. I used the same values. re 3.45 le .345. WHich one is right?

                        Comment


                        • #13
                          Re: Zobel calculation for woofers in series

                          Originally posted by brianpowers27 View Post
                          Whoah! I just modeled the crossover in the PCD. The zobel values it gives for 2 woofers wired in series are dramatically different. I used the same values. re 3.45 le .345. WHich one is right?
                          For two 4 ohm woofers, wired in series (yielding 8 ohms), your Zobel should most likely use an 8 or 9 ohm resistor (no big deal), and a cap that's in the 10uF to 14uF range. As I said before, the BEST way to determine these values is to run an actual impedance sweep on your woofers and determine the Zobel component values using some crossover simulator.

                          Chris

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                          • #14
                            Re: Zobel calculation for woofers in series

                            Thank you for your answer. I do not have any impedance testing equipment. I was surprised when I used the PCD and it calculated zobel values of 1.87uf and 20ohms. I expected the calculation to produce a slight variance but that is way out of the ballpark.

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                            • #15
                              Re: Zobel calculation for woofers in series

                              If you don't have an impedance sweep (and resulting .zma file), I would not be surprised if the PCD got a little wonky.
                              nothing can stop me now

                              Comment

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