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  • #16
    Without time there is not phase, perhaps you need to design a speaker or 2 more with that in mind.

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    • #17
      If you admit that you are wrong, I'll admit that I'm right. ;)
      Don't waste your money on a new set of speakers, you get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!

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      • #18
        I'm only as wrong as you are right, since the phase shifts with the frequency
        output of the driver so does the "time alignment". Explain the phase relationship
        between 2 drivers disregarding time and I'll be happy to admit my point is worthless.
        The term acoustic center is silly anyway.

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        • #19
          Originally posted by xmax View Post
          Notice they specify 2-3K region.]
          What they describe is not time alignment in the typical reference of time. Time alignment has to do with the impulse response. True time alignment does not necessarily align two drivers in the most useful way because it may not (likely will not) provide for optimal phase alignment in the crossover area. What they describe as time alignment is in reality phase alignment relative to the crossover area. In their example it's in the common crossover area of a 2-way system that is often 2-3 KHz. They describe the time delay as "The time delay is the group delay of the excess phase only." That does not change with frequency per se because the Group Delay is not a function of any single frequency. It's the rate of change of phase with frequency, the slope.

          If you offset two drivers such that the value of the group delay (the slope) is the same at any point in a frequency range, they you've phase-aligned them, meaning the phase curves of both overlap in that region.

          They are essentially describing the acoustic offset as a function of excess-phase and convert that time delay to the physical offset required in the 2-3KHz area so that the phase will align (and by extension the group delay) in that area for best summed result. They are removing the amount of excess-phase (time) required to phase-align, though they (IMO) confusingly call it time-alignment.They specify the physical offset required to achieve optimal results in the 2-3KHz area in the table, but this is, as I read it, for best phase results. Since the group delay for two drivers are not identical across the spectrum due to the fact that each driver is a band-pass device with differing phase responses and therefore differing group delays coupled with different acoustic centers due to the physical differences in the drivers, the optimal results are specified for the crossover area since this is the area of greatest driver interaction. Outside of crossover area the phase and group delays will deviate, but this is of little consequence to the summed response.

          Keep in mind as well that if you want to offset drivers to align the phase (group delay) in the crossover area, it's best done (IMO) with the crossover in place, although I've never done this.

          This is all totally different than determining acoustic offset in the sense that we usually use here. What that accomplishes is establishing the correct relative offset value for the specific physical location of drivers as mounted on a baffle together with the driver model created for the SPL files used (i.e. with any tails and subsequently generated minimum-phase).

          dlr
          WinPCD - Windows .NET Passive Crossover Designer

          Dave's Speaker Pages

          Comment


          • #20
            Originally posted by dlr View Post
            What they describe is not time alignment in the typical reference of time. Time alignment has to do with the impulse response. True time alignment does not necessarily align two drivers in the most useful way because it may not (likely will not) provide for optimal phase alignment in the crossover area. What they describe as time alignment is in reality phase alignment relative to the crossover area. In their example it's in the common crossover area of a 2-way system that is often 2-3 KHz. They describe the time delay as "The time delay is the group delay of the excess phase only." That does not change with frequency per se because the Group Delay is not a function of any single frequency. It's the rate of change of phase with frequency, the slope.

            If you offset two drivers such that the value of the group delay (the slope) is the same at any point in a frequency range, they you've phase-aligned them, meaning the phase curves of both overlap in that region.

            They are essentially describing the acoustic offset as a function of excess-phase and convert that time delay to the physical offset required in the 2-3KHz area so that the phase will align (and by extension the group delay) in that area for best summed result. They are removing the amount of excess-phase (time) required to phase-align, though they (IMO) confusingly call it time-alignment.They specify the physical offset required to achieve optimal results in the 2-3KHz area in the table, but this is, as I read it, for best phase results. Since the group delay for two drivers are not identical across the spectrum due to the fact that each driver is a band-pass device with differing phase responses and therefore differing group delays coupled with different acoustic centers due to the physical differences in the drivers, the optimal results are specified for the crossover area since this is the area of greatest driver interaction. Outside of crossover area the phase and group delays will deviate, but this is of little consequence to the summed response.

            Keep in mind as well that if you want to offset drivers to align the phase (group delay) in the crossover area, it's best done (IMO) with the crossover in place, although I've never done this.

            This is all totally different than determining acoustic offset in the sense that we usually use here. What that accomplishes is establishing the correct relative offset value for the specific physical location of drivers as mounted on a baffle together with the driver model created for the SPL files used (i.e. with any tails and subsequently generated minimum-phase).

            dlr
            Thank you, you clearly understand my point, I think common misconceptions are started with perhaps terms like "acoustic centers" and "time alignment".
            Designing with impulse response would be good especially if we only listened to recorded starter pistols or square wavs. Better terms would be nice
            but I'm just happy you understand what I am talking about. Hopefully some ^ will read this and learn a thing or 2.

            Comment


            • #21
              Originally posted by fatmarley View Post
              I get a weird phasey, cuppy, hollow type of sound with some speech, that I don't get with headphones.
              Looks like It was a wonky frequency response that was causing the problem. I think one of my measurement mics may need to be calibrated.

              Comment


              • #22
                Originally posted by xmax View Post
                Thank you, you clearly understand my point, I think common misconceptions are started with perhaps terms like "acoustic centers" and "time alignment".
                Designing with impulse response would be good especially if we only listened to recorded starter pistols or square wavs. Better terms would be nice
                but I'm just happy you understand what I am talking about. Hopefully some ^ will read this and learn a thing or 2.
                No, I countered your points.The reference is not overly useful to anyone other than those using their specific drivers. True time alignment does not shift with frequency since the speed of sound is not frequency dependent. You did not apparently understand what they were doing. It was not time alignment, it was phase alignment in a specific frequency range that they chose for a specific use.

                The term acoustic center has a meaning and is useful in understanding the acoustics of a driver. Misconception of the term time alignment does occur, as you seem to have misunderstood.

                dlr
                WinPCD - Windows .NET Passive Crossover Designer

                Dave's Speaker Pages

                Comment


                • #23
                  Different parts of the cone generate some frequencies more efficiently
                  than others, since the cone is not flat and flexes not all frequencies
                  arrive to the reference point at the same time. Please don't make me
                  prove this point to you. There is so much misunderstood data on
                  this forum hopefully our conversation has shed some light on the
                  subject whether you think I'm wrong or not. Good day sir.

                  Comment


                  • #24
                    Originally posted by xmax View Post
                    Different parts of the cone generate some frequencies more efficiently
                    than others, since the cone is not flat and flexes not all frequencies
                    arrive to the reference point at the same time. Please don't make me
                    prove this point to you. There is so much misunderstood data on
                    this forum hopefully our conversation has shed some light on the
                    subject whether you think I'm wrong or not. Good day sir.
                    I understand and agree with what you are saying. The good day sir is a little pissy though.
                    craigk

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

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                    • #25
                      I said good day!

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                      • #26
                        BTW I'm never more serious than a pretend candy factory owner if you did not get the reference.
                        I design audio equipment for a living what do I have to be pissy about. I'm good if you are good.

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                        • #27
                          Originally posted by xmax View Post
                          Different parts of the cone generate some frequencies more efficiently
                          than others, since the cone is not flat and flexes not all frequencies
                          arrive to the reference point at the same time. Please don't make me
                          prove this point to you. There is so much misunderstood data on
                          this forum hopefully our conversation has shed some light on the
                          subject whether you think I'm wrong or not. Good day sir.
                          Efficiency has nothing to do with it. Time alignment has to do with speed of sound only. You have shed no light on the topics so far.

                          dlr
                          WinPCD - Windows .NET Passive Crossover Designer

                          Dave's Speaker Pages

                          Comment


                          • #28
                            Silly math

                            Efficiency is a poor choice of words sorry.

                            http://orbit.dtu.dk/fedora/objects/o...439883/content

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                            • #29
                              Originally posted by dlr View Post
                              Efficiency has nothing to do with it. Time alignment has to do with speed of sound only. You have shed no light on the topics so far.

                              dlr
                              People that prefer to live in the dark will never see the light.
                              craigk

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

                              Comment


                              • #30
                                Acoustic centre calculations.

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