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Offsets, Asymmetrical Slopes, and Mysticism - revisited *PICS*

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  • #46
    Thanks for finding this thread, I found it very informative as well, even without the pictures.

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    • #47
      Originally posted by dkalsi View Post

      It is unfortunate that most of the pictures from this post are gone thanks for Photobucket. Such a valuable thread. Does an one have a copy of this Jeff's first post with the embedded pictures?

      I also wanted to ask a question in regards to Jeff's statement above:

      Does driver phase change/rotate based on the acoustic crossover order or the electrical crossover? For example, if there is 90 degrees phase rotation per order, would the the driver have 180 degrees phase rotation for a second order electrical, which lets assume resulted in effectively a 4th order acoustic crossover, or would it have 360 degrees of phase rotation (i.e., 90 degrees of each acoustic crossover order)?
      Total phase rotation is always tied to the acoustic slope. For example, when you use a 2nd order HP filter on a tweeter with a 2nd order roll-off, you create a 4th order acoustic slope and 4th order phase response.
      R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio
      Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51

      95% of Climate Models Agree: The Observations Must be Wrong
      "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

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      • #48

        Total phase rotation is always tied to the acoustic slope. For example, when you use a 2nd order HP filter on a tweeter with a 2nd order roll-off, you create a 4th order acoustic slope and 4th order phase response.
        The acoustic slope is the result of the filter and it's phase response, I think it is much more constructive to unthink the roll-off until the electrical aspects are worked out.
        Since a electrical 4th order filter would be 180 degrees out of phase with phase with a 2nd order acoustic plus second order electrical filter...
        Guess xmax's age.

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

        Comment


        • #49
          Originally posted by dkalsi View Post

          It is unfortunate that most of the pictures from this post are gone thanks for Photobucket. Such a valuable thread. Does an one have a copy of this Jeff's first post with the embedded pictures?

          I also wanted to ask a question in regards to Jeff's statement above:

          Does driver phase change/rotate based on the acoustic crossover order or the electrical crossover? For example, if there is 90 degrees phase rotation per order, would the the driver have 180 degrees phase rotation for a second order electrical, which lets assume resulted in effectively a 4th order acoustic crossover, or would it have 360 degrees of phase rotation (i.e., 90 degrees of each acoustic crossover order)?

          The only thing that can affect the phase of a filter is the filter itself, the acoustic roll off would only affect system phase and certainly not the same way removing a order from a filter.
          Guess xmax's age.

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

          Comment


          • #50
            Phase should be looked at as how a single filter affects phase difference between the input and output of said filter AND the Phase of the 2 drivers summing together and the phase that is created
            from that joyous union (compared to the source).
            Guess xmax's age.

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

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            • #51
              The true beauty of this post lies within the various concepts used to deal with driver offset (acoustic centre) Hey my tweeter is 90 degrees out of phase with my
              mid because they are both mounted on the same slab of hardened pulp and the mid-basses "centre" is about 1" further back than my tweets! Oh cool I can fix
              it with various topologies and "slopes" messing around with polarity or "relaxing orders" and end up with a phase f*CK free great sounding speaker!
              Guess xmax's age.

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

              Comment


              • #52
                Originally posted by xmax View Post

                The acoustic slope is the result of the filter and it's phase response, I think it is much more constructive to unthink the roll-off until the electrical aspects are worked out.
                Since a electrical 4th order filter would be 180 degrees out of phase with phase with a 2nd order acoustic plus second order electrical filter...
                If I am reading you right, then this is incorrect. An acoustic second order roll-off (say, a tweeter's response) combined with an electrical second order roll-off will have an acoustic 4th order roll-off and the phase will be exactly that of an equivalent 4th order electrical circuit by itself. This is by definition how minimum phase works.We should wouldn't be able to design predictable crossovers if it didn't.
                Click here for Jeff Bagby's Loudspeaker Design Software

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                • #53
                  Originally posted by xmax View Post

                  The acoustic slope is the result of the filter and it's phase response, I think it is much more constructive to unthink the roll-off until the electrical aspects are worked out.
                  Since a electrical 4th order filter would be 180 degrees out of phase with phase with a 2nd order acoustic plus second order electrical filter...
                  When designing acoustic systems, it is only the acoustic response that matters. If you're shooting for 4th order crossovers then you must first see what the acoustic response of the transducer is doing in the region where you want to cross it. If you have a wide band midrange for example that has flat response from 100Hz to 5000Hz, but you want to cross it at 500Hz to a woofer with a 4th order slope, you would likely need a 4th order electrical filter. But if you wanted to cross it at 200Hz, then you'd likely only need a second order electrical filter because the system response is the convolution of the natural response of the driver and the response of the filter.

                  You cannot "unthink" the roll off because it is just as important as the filter.
                  R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio
                  Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51

                  95% of Climate Models Agree: The Observations Must be Wrong
                  "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

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                  • #54

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                    • #55
                      Originally posted by dkalsi View Post
                      Pete/Jeff, Your responses were very helpful. I have one follow up question: What does it mean to “relax” the crossover slope? Does it mean (as an example say) the process of foregoing a true LR4 “target” curve for the purpose of better phase/acoustic sum between driver? There are several threads here that refer to “relaxing” the network but I have yet to see it explained/defined. Thanks, D Sent from my iPhone using Tapatalk
                      You can get an idea of non-symmetric crossovers do when there's an offset. I created a small app when experimenting with and verifying crossover targets in WinPCD. The app is WinFilters and can be downloaded at my site. It lets you select various highpass and lowpass target types, orders and Fc. One thing I found interesting afterwards was in the area of what is often called "relaxing". With the default of no offset when it starts you'll see what would either be an electrical summed response (not really useful) or a two-way system with no relative acoustic offset. You can then add delay to either woofer or tweeter to see the change. What I found interesting in playing with it is the summed response with tweeter at LR4, an offset in the woofer and then selecting various woofer lowpass and/or Fc options.

                      For example, with a typical woofer offset, you cannot get an ideally summed response with any standard woofer lowpass. You can get a nearly flat response in some cases, but in this case you will always have something of a lobe off-axis somewhere. It's unavoidable. But on-axis is most important. What I found was how close to flat an LR4 tweeter would sum with other crossover types & orders. For example:

                      B4-LR6 25mm offset (total distance):

                      Click image for larger version

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                      LR8-LR8 25mm offset (total distance):

                      Click image for larger version

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                      What we call "relaxed" slopes may actually be closer to some other crossover type/slope/Fc. No matter the type, there will almost always be some amount of off-axis lobing, just as there is with odd-order Butterworth that is flat on-axis

                      dlr
                      WinPCD - Windows .NET Passive Crossover Designer

                      Dave's Speaker Pages

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                      • #56
                        Good explanation Dave
                        Click here for Jeff Bagby's Loudspeaker Design Software

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                        • #57
                          Originally posted by Jeff B. View Post

                          If I am reading you right, then this is incorrect. An acoustic second order roll-off (say, a tweeter's response) combined with an electrical second order roll-off will have an acoustic 4th order roll-off and the phase will be exactly that of an equivalent 4th order electrical circuit by itself. This is by definition how minimum phase works.We should wouldn't be able to design predictable crossovers if it didn't.

                          Although it certainly would be nice if you could add 2 more "orders" to a filter and maintain the same phase (2nd vs 4th order at the corner frequency)
                          I do not find that the case.
                          Guess xmax's age.

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

                          Comment


                          • #58
                            Originally posted by dkalsi View Post
                            Pete/Jeff, Your responses were very helpful. I have one follow up question: What does it mean to “relax” the crossover slope? Does it mean (as an example say) the process of foregoing a true LR4 “target” curve for the purpose of better phase/acoustic sum between driver? There are several threads here that refer to “relaxing” the network but I have yet to see it explained/defined. Thanks, D Sent from my iPhone using Tapatalk

                            In some cases "relaxing" the slope would be removing an "order" say 4th order to 3rd order.
                            Guess xmax's age.

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

                            Comment


                            • #59
                              Originally posted by xmax View Post


                              Although it certainly would be nice if you could add 2 more "orders" to a filter and maintain the same phase (2nd vs 4th order at the corner frequency)
                              I do not find that the case.
                              I think you need to read the post again. Because that is not what he said at all.
                              Last edited by craigk; 11-06-2017, 10:24 AM.
                              craigk

                              " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

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                              • #60
                                Originally posted by xmax View Post


                                Although it certainly would be nice if you could add 2 more "orders" to a filter and maintain the same phase (2nd vs 4th order at the corner frequency)
                                I do not find that the case.
                                You don't maintain the same phase. The phase follows whatever the ultimate acoustic roll-off is, and that is a combination of the filter and the driver's roll-off. Crossover components and loudspeakers are minimum phase devices, this means the phase is now predictable (very accurately, I might add). what you are describing would be non-minimum phase.
                                Click here for Jeff Bagby's Loudspeaker Design Software

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