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

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  • #61
    Perhaps you missed "at the corner frequency".

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    • #62
      Originally posted by xmax View Post
      Perhaps you missed "at the corner frequency".
      It seems that you don't quite understand the difference between the system response and the filter response. When you are designing an acoustic system, the phase of the system is directly related to the acoustic output of the device in question. Of course the electronics has a role in shaping that response, but no more so than the natural response of the transducer.

      If you design a crossover that requires the acoustic output be down 6dB at 300Hz, and the driver is already beginning its roll off and is down 2dB at 300Hz, then your filter should be down 4dB at 300Hz in order to meet the target acoustic response. The transfer function of the filter needs to be multiplied by the transfer function of the transducer to predict the final response you're after. They can't be separated unless you're talking about something like a full range device being filtered somewhere octaves away from a natural roll off.
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      • #63
        I understand it quite well actually and thank you for your "insight". I'm only trying to clarify the topic for people that don't
        already know everything. It seems relatively clear to most people that adding a order to a passive filter will shift the
        phase 90 degrees, so obviously going from 2nd to 4th order will shift the (electrical) phase 180 degrees specifically at
        the corner frequency and shift the out of band phase dramatically as well. All of this effects the acoustic roll off (of course)
        which in turn affects lobbing and slew of things I don't have time to go into.

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        • #64
          Originally posted by xmax View Post
          It seems relatively clear to most people that adding a order to a passive filter will shift the
          phase 90 degrees, so obviously going from 2nd to 4th order will shift the (electrical) phase 180 degrees specifically at
          the corner frequency and shift the out of band phase dramatically as well. All of this effects the acoustic roll off (of course)
          which in turn affects lobbing and slew of things I don't have time to go into.
          The only situation in which this would be true is if the electrical filter were close to being an ideal electrical filter that happened to work with the properties of the driver it was designed for. However, since there are very few cases in which an ideal electrical filter can work when combined with the acoustical (and electrical) properties of a driver, adding another order to the electrical filter will very likely not achieve a typical acoustic response, at Fc or otherwise. There is more to be considered than the response at Fc. There is no guarantee that even at Fc the phase will rotate precisely or even close to 180 degrees in your example.

          dlr
          WinPCD - Windows .NET Passive Crossover Designer

          Dave's Speaker Pages

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          • #65
            Originally posted by xmax View Post
            I understand it quite well actually and thank you for your "insight". I'm only trying to clarify the topic for people that don't
            already know everything. It seems relatively clear to most people that adding a order to a passive filter will shift the
            phase 90 degrees, so obviously going from 2nd to 4th order will shift the (electrical) phase 180 degrees specifically at
            the corner frequency and shift the out of band phase dramatically as well. All of this effects the acoustic roll off (of course)
            which in turn affects lobbing and slew of things I don't have time to go into.
            I don't mean to insult you, but it doesn't seem that you understand what we're saying. at least you're not communicating that in what (and the way) you reply.
            Click here for Jeff Bagby's Loudspeaker Design Software

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            • #66
              2nd and 4th order filters will have dramatically different phase characteristics regardless of acoustical roll off.

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              • #67
                Originally posted by xmax View Post
                2nd and 4th order filters will have dramatically different phase characteristics regardless of acoustical roll off.
                Quite the non-sequitur.

                dlr
                WinPCD - Windows .NET Passive Crossover Designer

                Dave's Speaker Pages

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                • #68
                  Hopefully that is simple enough, approximately 180 degrees is about as different as it gets, last I checked.

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                  • #69
                    Originally posted by xmax View Post
                    2nd and 4th order filters will have dramatically different phase characteristics regardless of acoustical roll off.
                    definitely a non-sequitur with regard to what we are discussing, but it does seem to prove my point.
                    Click here for Jeff Bagby's Loudspeaker Design Software

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                    • #70
                      Originally posted by xmax View Post
                      Hopefully that is simple enough, approximately 180 degrees is about as different as it gets, last I checked.
                      I suppose that when discussing xo topologies at a given impedance, what you're saying makes sense. The problem (as Dave, Pete, and Jeff have pointed out) is that nearly every driver's inherent transfer function will muck up that theoretical response. And IME, relaxing the slope would be a situation where the overall acoustic slope would start at, say, LR2 at the knee, then resolve to the originally desired LR4.
                      You go your way, I'll go mine. I don't care if we get there on time.

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                      • #71
                        I'm only speaking of the phase (relationship between 2 or more drivers) and how it is affected by the
                        electrical filter slope. I don't mean to insult any of you but please stop being A holes.

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                        • #72
                          Originally posted by xmax View Post
                          I'm only speaking of the phase (relationship between 2 or more drivers) and how it is affected by the
                          electrical filter slope. I don't mean to insult any of you but please stop being A holes.
                          Now there's some projection.

                          dlr
                          WinPCD - Windows .NET Passive Crossover Designer

                          Dave's Speaker Pages

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                          • #73
                            Originally posted by xmax View Post
                            I'm only speaking of the phase (relationship between 2 or more drivers) and how it is affected by the
                            electrical filter slope. I don't mean to insult any of you but please stop being A holes.

                            Focusing on only the electrical filter's contribution to the acoustic output of the driver is only half the story, but ok, let's look at that. What is your position exactly?
                            ~Brandon

                            Soma Sonus
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                            • #74
                              Originally posted by xmax View Post
                              2nd and 4th order filters will have dramatically different phase characteristics regardless of acoustical roll off.

                              The difference between those two filters (180 degrees) will be directly applied to the driver's acoustic response, so I'm not sure what you mean by "regardless"? It almost sounds like you are saying "all things equal" which of course the final response can't possibly be equal going from 2nd to 4th order filters.
                              ~Brandon

                              Soma Sonus
                              DriverVault

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                              • #75
                                Originally posted by xmax View Post
                                I'm only speaking of the phase (relationship between 2 or more drivers) and how it is affected by the
                                electrical filter slope. I don't mean to insult any of you but please stop being A holes.

                                Mr XMAX - these are basically the nicest people you will ever meet on the internet.

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