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Now THAT is a crossover

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  • #46
    Originally posted by johnk... View Post

    Horrible lobing yes, constrained to 6db/oct, no.
    Actualy, yes. If making a true constant voltage in the Small paper sense, the HP or LP total (acoustic) transfer function is subtracted from unity. The derived function results in an acoustic transfer function asymptotic to first order. i proved this analytically and in simulation in my 4th year EE project in the 80s (looking at all axes). All my grading EE profs would disagree with you. Unfortunately given the era, it was written on a typerwriter and sims are on a Vax plotter so can't be shared as a pdf.

    Love it, made one post in after a million years trying to be helpful and already a smarmy snotty drive by response. Why? Ciao. enjoy being miserable!

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    • #47
      Actually NO. Small showed in perhaps another paper that you can make symmetric CV crossovers with any order asymptotic slope. He presented several. I looked at the one that had second order asymptotic slopes. I was able to decompose the HP and LP section into symmetric 2nd order filters with staggered corner frequencies and a PEQ section to make the response flat. I wrote a paper on it which appeared in Audio Xpress in 2001. Here is a link to a Wayback page from my old geocities site that has the transfer functions. It is of the form 1 = (HP' + LP') = ( HP + LP) * EQ , or 1/(HP + LP) = EQ. The key is to choose HP and LP symmetric about the center frequency and so they sum to a minimum phase response. Then minimum phase EQ can be applied to flatten the response and recover flat phase. At the time I did the same analysis for higher order filters but EQ, becomes a mess, and it's of academic interest only. Of course, with today's digital filter hardware you could simply program EQ = 1/(HP + LP). In the 2nd order case, HP, LP and EQ are all biquads.

      http://web.archive.org/web/200908092...overdocN3.html.

      Lobing is the problem as, like a Butterworth crossover you get a null to one side and a peak to the other. Except where as the Butterworth peak is 3dB, the 2nd order TP crossover has a 6dB peak off axis.

      John k.... Music and Design NaO dsp Dipole Loudspeakers.

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      • #48
        Wait are you using active EQ?

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        • #49
          The best way to do it would be with active EQ, but theoretically it can be done, for the 2nd order crossover, using passive EQ. The problem is that passive EQ results in attenuation and wasted power. But frankly, with the advent of simple and inexpensive DSP processing and multi amplification I can't imagine why anyone would actually design a transient perfect system using a passive approach. It is overly complicated, as in the case of the crossover that was the subject of this post originally, and the performance would be marginal compared to what can be achieved using dsp.

          FYI, I have attached a copy of my 2000 paper dumm9.pdf

          And with the poor polar response it doesn't make sense to me to use anything but linear phase filters and FIR processing which can yield the typical LR type symmetric polar response.
          Attached Files
          John k.... Music and Design NaO dsp Dipole Loudspeakers.

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          • #50
            After watching Javad's video on crosstalk, I can imagine that crossover having lots of it.

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            • #51
              Originally posted by hardcorecap View Post
              After watching Javad's video on crosstalk, I can imagine that crossover having lots of it.
              Do you have a link to that video? I'm a member of that group, but the FB user interface is so bad I can't find it. It probably doesn't help that I usually stay away from FB.

              Thanks, Ed
              "Everything is nothing without a high sound quality." (Sure Electronics)

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              • #52
                Finally found it, very informative.

                [url]https://www.facebook.com/jshadzi/vid...OlwiXCJ9In0%3D[/url]
                "Everything is nothing without a high sound quality." (Sure Electronics)

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                • #53
                  Ed, I assume it is this one based on the title, but Hardcorecap please correct me if I'm wrong.

                  https://www.youtube.com/watch?v=k-NUZQ10PMQ

                  .

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                  • #54
                    Originally posted by a4eaudio View Post
                    Ed, I assume it is this one based on the title, but Hardcorecap please correct me if I'm wrong.

                    https://www.youtube.com/watch?v=k-NUZQ10PMQ

                    .
                    yeah, that's the one.

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                    • #55
                      Thanks for the link. I eventually found it on FB, but didn't know it was on Youtube too. Gotta love those inductors clacking together.
                      "Everything is nothing without a high sound quality." (Sure Electronics)

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