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  • #61
    ^Yes, there are few places. Time offset is needed also with dual channel measurements e.g. if all measurements have extra delay and excessive wrapping at high frequencies makes phase responses in graphs fuzzy and reduces accuracy of phase response calculation. Or you have stepped baffle or deep horn, and drivers need to be located physically at correct distance from common reference point on front baffle.

    First option is to adjust physical location of driver instance in the crossover. Positive Z coordinate in mm moves driver further from listener, and negative to closer. X,Y,Z mm simulates physical location of the driver compared to common reference point on the baffle. Common reference point 0,0,0 is typically perpendicular point of listening axis on baffle surface.

    Second option is to adjust Delay [us] of driver's frequency responses. Scale in dB, delay in us and polarity inversion adjustments in Drivers tab are meant for normalizing frequency response data of that driver model. Note that Delay adjustment is not exactly same as location adjustment with X,Y,Z coordinates because delay offset effects to all off-axis directions, but Z-coordinate more to 0 deg and 180 deg directions, and less to 90 deg.
    Last edited by kimmosto; 11-01-2018, 02:37 PM.

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    • #62
      Originally posted by kimmosto View Post
      As far as I know, OmniMic v2 is single channel gear which is not able to measure sound flying time so timing/phase differences between different measurements and drivers are not included in exported response data. That would make life quite hard if target is to simulate multi-way speaker with VituixCAD (or any other software) which calculates off-axis responses in both planes, power and DI responses by polar measurements and simulated crossover. Recommended measurement gear is "normal" analog with two input and output channels and external (or internal) time reference with loop back in the second channel.
      I have to disagree. Measured phase is most definitely not a requirement. Actually, quite the opposite. If measured phase is used exclusively, then determining the absolute acoustic center of each driver would be required to model off-axis responses accurately. But it's not possible to accurately determine absolute acoustic center, which is why relative acoustic center has been used going back at least to the 80's. I first used CALSOD in the mid-90s, initially using the LMS measurement system which cannot measure phase. It had a built-in tailing function for use in generating minimum-phase of the resulting SPL response. However, that alone is insufficient. What is required is the three-measurement scheme to determine relative acoustic offset, as detailed in my SpeakerBuilder article here.

      What this provides is a set of minimum-phase SPL responses that allow for easy determination of acoustic offset. With that offset and those specific (not to be further modified) files any software which can model off-axis response will show accurate off-axis response based on the crossover. The one caveat, a big one of course, is that variations due to diffraction differences in the off-axis are not taken into account, but the direct on-axis response which does have that if taken from measurements in situ of the box will include diffraction at the test point, which is often the listening position or close to it.

      I have and will continue to point out the usefulness of this process for minimum-phase files. Again, it is not necessary to measure phase for basic crossover work. Since absolute acoustic center is, at best, an estimate, using relative acoustic offset provides precise offset values, as long as those SPL files are not further modified. The OmniMic is fully adequate for the task.

      My software, WinPCD, has built in functions to automatically calculate vertical/horizontal responses and for the entire front hemisphere in 5 degree increments and as long as minimum-phase files are used. Measured phase is immaterial and, in fact, not usable for this.

      dlr
      WinPCD - Windows .NET Passive Crossover Designer

      Dave's Speaker Pages

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      • #63
        Originally posted by kimmosto View Post
        This is usually just useless theory,
        No, it's not. Context, that is what measurement system is in use and how the results will be used, in fact, makes it quite relevant.

        ...because measurement programs decide (without asking us) how they behave if reference channel is not available or not in use.
        Not necessarily. Again, it is dependent on the measurement system. I have used a number of measurement systems and all but one provided manual placement of the start time marker.

        So in practice semi-dual or dual channel connection and dual channel (timing reference) mode is usually mandatory, and therefore recommended in this thread.
        Again, I beg to differ, quite the contrary in my experience. I almost never use measured phase, only doing so when making simple, single-point measurements for initial modelling prior to a full-fledged, minimum-phase, full front hemisphere investigation as part of the design process.

        dlr
        WinPCD - Windows .NET Passive Crossover Designer

        Dave's Speaker Pages

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        • #64
          I am now using a closed loop system (a pair of Cross-Spectrum calibrated mics + FuzzMeasure + RME Babyface Pro interface with loop back) and for me, it works much better than Omnimic.

          I use measured phase (time of flight built-in) and for off-axis, I just measure.

          Again, this is what works for me, YMMV, but I would never go back to using Omnimic.

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          • #65
            Originally posted by Audiotorium View Post
            I am now using a closed loop system (a pair of Cross-Spectrum calibrated mics + FuzzMeasure + RME Babyface Pro interface with loop back) and for me, it works much better than Omnimic.

            I use measured phase (time of flight built-in) and for off-axis, I just measure.

            Again, this is what works for me, YMMV, but I would never go back to using Omnimic.
            Same, but with ARTA. I could never get reliable results extracting minimum phase. I compensate for most of the time of flight delay in VituixCAD to resolve the phase wrapping problems at HF.'

            I must have tried a hundred times, but I never got measurements from ARTA to work in the acoustic offset calculators out there. Doing a semi-2 channel measurement is much more intuitive for me.

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            • #66
              Originally posted by Audiotorium View Post
              I am now using a closed loop system (a pair of Cross-Spectrum calibrated mics + FuzzMeasure + RME Babyface Pro interface with loop back)...
              I use measured phase (time of flight built-in) and for off-axis, I just measure.
              This is simple, fast and robust measurement method. No need to play with three measurement system, minimum phase extraction with manual slope settings and assume that all radiators (in the same speaker) are minimum phase and delay/phase behavior to all directions is equal.

              Most USB mics with separate sound card for output probably have that much timing stability that acoustic centers can be defined with three measurements. But some point timing might suddenly jump 1-2 ms without any change in settings or processor load. Some products (mics, sound cards, PCs, OSs) could be more stable than the others, but dual channel gear and measurement mode is easier option to ensure that random jumps or forced normalization of IR to e.g. 0 ms or 300 samples will not happen, and measurements are instantly valid for off-axis summing assuming that geometry is known. Time window could cause some non-minimum phase behavior at low frequencies but that is different story.

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              • #67
                Unfortunately I need FR response below 400 Hz without room interactions for decent level matching to the mid or tweeter so I'm splicing and extracting min phase. I also have OCD where I feel obligated to trim the tweeter tails. civit if you need help determining acoustic offsets I'd be happy to walk you through it.
                John H

                Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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                • #68
                  Originally posted by jhollander View Post
                  Unfortunately I need FR response below 400 Hz without room interactions for decent level matching to the mid or tweeter so I'm splicing and extracting min phase. I also have OCD where I feel obligated to trim the tweeter tails. civit if you need help determining acoustic offsets I'd be happy to walk you through it.
                  The tweeter tails are straightforward and easy. The highpass is a closed box, so below the measurement cutoff, it will still be a pure 12db, so extending it won't introduce any consequential SPL difference from what might be measured. The top end lowpass is always a bit problematic with regard to knowing the actual SPL due to measurement system limitations and driver breakup, but it's is also inconsequential to design in that it is, in all cases I've ever seen, nowhere close to any crossover Fc. Since you generate phase from the final model, as long as you do use the three measurement system and then don't modify the driver SPL tails afterwards, you'll be able to get a nearly perfect match between measured and modeled summed response. The relative offset you need to determine is a function of the driver models. Once set,on a specific axis, you're good to go.

                  I guess then that I'm also OCD if doing that is an indication of it!

                  dlr
                  WinPCD - Windows .NET Passive Crossover Designer

                  Dave's Speaker Pages

                  Comment


                  • #69
                    Agreed. I've added a few super tweeters where the early phase wrap of the mid-tweeter gets close to affecting with the super tweeter phase. Certainly the slope of the mid tweeter phase changed by adjusting the HF mid tweeter tail. Probably not meaningful but it does make an argument for extending the high frequency measurement window imo.
                    John H

                    Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

                    Comment


                    • #70
                      Originally posted by dlr View Post
                      The tweeter tails are straightforward and easy. The highpass is a closed box, so below the measurement cutoff, it will still be a pure 12db...
                      Not always. Also steeper than closed 12 dB/oct exist, though extending of e.g. 18 dB/oct slope is as easy. But extending is not mandatory with measured phase with tweeters because low frequencies are high passed by the crossover and possible problems due to S/N while measurement will not be visible in simulated total.

                      VituixCAD is able to crop and extend responses at both ends with minimum phase calculation. User can adjust cropping frequencies and slopes, or leave that job to program at high frequencies, because constant manual slope is not always the best choice for all responses including off-axis. This feature is in Calculator tool so processing can be done to all off-axis responses at once. VituixCAD is also capable to help with defining difference in acoustic centers with three measurement method or directly by difference in excess group delay if measured phase is still available and stable (measured with time reference ie dual channel).
                      Other than VituixCAD "total" users are also welcome to use those features in case measurement gear is not dual channel or stable/good enough for designing with measured phase, or cropping + extending with MP manipulation is needed otherwise.
                      Last edited by kimmosto; 11-03-2018, 04:04 AM.

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                      • #71
                        Well then, I think we have agreed that measurements can be done with either single or dual channel setups. I have used both methods with equal success. But as always, the devil is in the details.
                        "Everything is nothing without a high sound quality." (Sure Electronics)

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                        • #72
                          Single channel with MP extraction has chances when simulating axial only, but off-axis - especially with combination of surface mounted flat and deep/non-flat drivers such as horns is something between uncertain and mission impossible if geometry simulation is based on simple x,y,z coordinates without smarter (TL/horn/wave guide) simulation which could compensate variable length route of sound wave. Therefore I prefer and recommend dual channel gear and mode only. Makes my life much easier and keeps other options still available.

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                          • #73
                            Originally posted by kimmosto View Post
                            Single channel with MP extraction has chances when simulating axial only, but off-axis - especially with combination of surface mounted flat and deep/non-flat drivers such as horns is something between uncertain and mission impossible if geometry simulation is based on simple x,y,z coordinates without smarter (TL/horn/wave guide) simulation which could compensate variable length route of sound wave. Therefore I prefer and recommend dual channel gear and mode only. Makes my life much easier and keeps other options still available.
                            I suppose I should have said that typical tweeters are 12db highpass rolloff. I have yet to work with a tweeter that was not, but I work only with ordinary type tweeters, not horn a large wave guided ones and of course with tweeters the measurements often go into the noise floor, so assuming as 12db rolloff for typical tweeters is a valid assumption for most cases.

                            Off-axis it's best to measure to have the most accurate curves as well, of course, but the variation in response due to atypical drivers is, I suspect, not significant with respsect to the changes in excess-phase in the off-axis. For examining the off-axis due to the crossover, I don't see it as being a big factor. Much bigger is the variation due to diffraction differences, so the model would need to include that and would be dependent on how accurate that influence is to the off-axis.

                            If the measurements are taken on-axis in situ of the baffle, then to be accurate, the on-axis would have to have the measurement normalized to remove the on-axis diffraction, essentially transforming them into quasi-anechoic responses, then adding the diffraction back in for the off-axis influence. If off-axis diffraction simulation is added to direct, on-axis measurements, than any and all off-axis simulations will be inaccurate. This sort of thing gets more convoluted if all factors are to taken into account in a single software package. Ultimately, this devolves to taking quasi-infinite baffle measurements, then modeling all aspects with these minimum-phase responses.

                            dlr
                            WinPCD - Windows .NET Passive Crossover Designer

                            Dave's Speaker Pages

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                            • #74
                              IMO the best option, if one wants accurate off-axis to use in optimizing a system, is to take multiple off-axis measurements and feed them into a system that can optimize the crossover taking these into account. In fact, while limited in number of measurements that can be imported, CALSOD, the DOS design software I started using in 1995 that had its origins, I believe, in the late 80's, had the ability to import multiple measurements, apply some basic diffraction influence (e.g. baffle step, etc.), set weighting schemes to each measurement, and optimize for that and other optional influences. This ran on IBM-PC 286 systems. CALSOD can still run in Windows 7 (I haven't tried Win10, it probably will). It's clunky, but I used it for final crossover work for a long time, even after having newer software.

                              This package is what taught me that measured phase isn't a requirement for excellent crossover design.

                              dlr
                              WinPCD - Windows .NET Passive Crossover Designer

                              Dave's Speaker Pages

                              Comment


                              • #75
                                Originally posted by dlr View Post
                                IMO the best option, if one wants accurate off-axis to use in optimizing a system, is to take multiple off-axis measurements and feed them into a system that can optimize the crossover taking these into account.
                                Here we have that kind of software. Have you considered testing or discussion about VituixCAD, or are you just defending your measurement gear, software and methods?

                                Originally posted by dlr View Post
                                This package is what taught me that measured phase isn't a requirement for excellent crossover design.
                                We could also say that it is possible to design very good speakers without measured phase or without off-axis measurements or maybe without measurements at all. It is just designer's choice how much accurate simulation information he/she requires or would like for see to get better forecast in each different case, or how much rely on luck or excellent acoustic basic design or experience or cloning from some other designs - or ears. Corrupting measured phase by default is one step towards blindness and ignorance.
                                Last edited by kimmosto; 11-04-2018, 01:34 PM.

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