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  • Passive Line Level Xovers, any love?

    Passive line level XOs are not talked about much around here, https://www.marchandelec.com/
    sells some kits but they can get rather expensive. I have used my own design in a few studio
    monitors in combination with traditional passive XOs and analog active filters. Zack Brown's
    Southern Ground Nashville rocks 2 sets of monitors using this arrangement; a set of large
    soffit mounted "mains" with 3" Volt mids and Satori Beryllium tweets (and 18" Ultimax,12" SB etc!)
    and a set of 3 way "Near Fields" using SB/Tang Band/Dayton RSS.

    Both systems use a fully balanced passive line level XO as a HP for the mid and tweet.
    I choose a 2nd and 3rd order "Butterworth" alignment for it's desired (measured and confirmed) transfer
    function. Has anybody else up in here dabbled in line level XO design?
    Guess xmax's age.

    My guess: 15. His grammar is passable. His trolling is good.

  • #2
    I dabbled with these, 40 years ago. Working with tubes you almost had to go passive. After I learned how to make 4th order active with op-amps I never used passive again.
    www.billfitzmaurice.com
    www.billfitzmaurice.info/forum

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    • #3
      My "go to" is 4th order active when it comes to line level, however, passive line level
      can be fun and some might say they can sound "nice".
      Guess xmax's age.

      My guess: 15. His grammar is passable. His trolling is good.

      Comment


      • #4
        A PLL Xover network is termianted/loaded by the input impedance of the amplifier or whatever it is connected to. The problem is that there is no standard input impedance (ir's just a resistor) value, and could be anything between 3k and 100k. You need to incorporate this impedance into the PLL Xover design, and this limits portability in general, or if you move it from system to system the response might change. If you could add a terminal active buffer then this would no longer be an issue, but that would no longer be a PLL Xover.

        The same sort of problem happens with passive volume controls. You could completely fix the problem by adding a buffer, but then it is no longer a passive system. Without a buffer it's not a good approach IMHO.
        Charlie's Audio Pages: http://audio.claub.net

        Comment


        • #5
          Originally posted by charlielaub View Post
          A PLL Xover network is termianted/loaded by the input impedance of the amplifier or whatever it is connected to. The problem is that there is no standard input impedance (ir's just a resistor) value, and could be anything between 3k and 100k. You need to incorporate this impedance into the PLL Xover design, and this limits portability in general, or if you move it from system to system the response might change. If you could add a terminal active buffer then this would no longer be an issue, but that would no longer be a PLL Xover.

          The same sort of problem happens with passive volume controls. You could completely fix the problem by adding a buffer, but then it is no longer a passive system. Without a buffer it's not a good approach IMHO.
          I'm generally using a known input impedance of 47K (Hypex N-core) so I use a load resistor of 10K and it "swamps" 47K (and most input stages)
          input impedance.

          In this particular system the balanced passive system gave us the best measurable performance without adding eq vs active 4th order.
          Guess xmax's age.

          My guess: 15. His grammar is passable. His trolling is good.

          Comment


          • #6
            Click image for larger version

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            Guess xmax's age.

            My guess: 15. His grammar is passable. His trolling is good.

            Comment


            • #7
              For the reasons Charlie explained, at line level it just makes more sense to use an active circuit if you want to stay in the analog domain, or use DSP. When an active alternative exists, I look at PLL and think "what's the point?". A serious question, why would someone choose to design a PLLXO instead of using an active circuit? I guess one could argue about adding op-amps in the signal path is "bad", but I've tried to pick out the difference in sound by adding and removing an op-amp from the signal path, with a modern "hifi" op-amp I simply couldn't tell.

              In any case, there's some discussion over at DIYAudio about PLLXO.
              "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
              exactly a Fc 3K for both drivers, anybody can do it." -Xmax

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              • #8
                It sounds to me that passive line level filters can be excellent but must be tuned to it's particular system. I'm not surprised by this conclusion, great sounding systems usually take much effort.

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                • #9
                  All passive circuits must be designed (tuned) for the load. "Normal" high level passive crossover must be designed for the load of the speaker. A line level passive crossover must be designed for the load of the amplifier input. A PLLXO, like an active system, requires a separate amplifier for each driver, so if you're going to go that route, why not just go all the way active or use modern DSP with all the benefits and conveniences it provides.
                  "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
                  exactly a Fc 3K for both drivers, anybody can do it." -Xmax

                  Comment


                  • #10
                    Originally posted by dcibel View Post
                    For the reasons Charlie explained, at line level it just makes more sense to use an active circuit if you want to stay in the analog domain, or use DSP. When an active alternative exists, I look at PLL and think "what's the point?". A serious question, why would someone choose to design a PLLXO instead of using an active circuit? I guess one could argue about adding op-amps in the signal path is "bad", but I've tried to pick out the difference in sound by adding and removing an op-amp from the signal path, with a modern "hifi" op-amp I simply couldn't tell.

                    In any case, there's some discussion over at DIYAudio about PLLXO.
                    I was going through a passive inductor based "phase" if you will. I designed it with PLLXO for that reason I suppose. But after we installed
                    it in the soffit the response was obviously greatly altered and being the type whom is never satisfied I switched the XO to Active LR4
                    thinking we would have better control for tuning. I was wrong, so we went back to PLLXO (just on the HP of the 3" Volt and SB Be combo
                    using a standard passive XO) and it's B3 transfer function gave us the best results both with summation of phase and FR. The rest of the
                    system is active LR4.
                    Guess xmax's age.

                    My guess: 15. His grammar is passable. His trolling is good.

                    Comment


                    • #11
                      Beyond simple matching of the PLL to line level source impedance and amp load impedance, Some line level stages don’t like driving a reactive load, some amps don’t like being driven by a reactive source impedance. Not like could mean increased distortion, reduced bandwidth or something else. Problem is amps and line level stages are black boxes in these regards so it’s a crap shoot what the secondary impact of the PLL will be, requiring significant extra testing

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                      • #12
                        Originally posted by DDF View Post
                        Beyond simple matching of the PLL to line level source impedance and amp load impedance, Some line level stages don’t like driving a reactive load, some amps don’t like being driven by a reactive source impedance. Not like could mean increased distortion, reduced bandwidth or something else. Problem is amps and line level stages are black boxes in these regards so it’s a crap shoot what the secondary impact of the PLL will be, requiring significant extra testing
                        If I didn't design the following stages and knew the source is a API desk able to start fires with it's monitor outputs
                        I would not have even considered it.
                        Guess xmax's age.

                        My guess: 15. His grammar is passable. His trolling is good.

                        Comment

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