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  • XSIM and Omnimic Z-offset

    If I collect my FRD files from Omnimic software, do I still need to manually enter a z-offset in XSIM, or does the "Summing Curve Phase" portion of the Omnimic software automatically add it to the FRD files. If I do need to enter it, is it a positive or negative value for the woofer? On a flat baffle, I assume the acoustic center of the woofer is behind the tweeter.
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  • #2
    Yes. In XSim, the Z offset is called "mod delay." Attached is my "XSim step-by-step" pdf. The mod delay setting is covered in step 26. Hope this helps. Bill

    XSim Step by Step.pdf
    SideTowers: http://techtalk.parts-express.com/fo...corundum-build
    Totally Flat: http://techtalk.parts-express.com/fo...5-totally-flat
    Plumber's Delight: http://techtalk.parts-express.com/fo...notech-winners
    Linehopper: http://techtalk.parts-express.com/sh...Esoteric-build

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    • #3
      Bill, thanks a ton!! That is super helpful. This is probably more suited for the Omnimic section, but do you prefer using the "summing Curve Phase" in Omnimic or just adjusting the "mod delay" in X-sim? It seems if I adjust the summing curve phase in omnimic, the "both" curve matches the summed curves in XSIM fairly well.

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      • #4
        Ok, my mistake. I misunderstood what you were asking. I never use the "driver FRD capture guide" built into OmniMic. I always calculate it in XSim.

        So, if OmniMic's guide is adjusting the phase, you don't want to double count it in XSim. The only question is, "Which method is more accurate?" When you adjust the phase in OmniMic, is this just a guesstimate based on the physical postion of the drivers? Or does OmniMic somehow match up the raw measurement data to produce a more accurate result?
        SideTowers: http://techtalk.parts-express.com/fo...corundum-build
        Totally Flat: http://techtalk.parts-express.com/fo...5-totally-flat
        Plumber's Delight: http://techtalk.parts-express.com/fo...notech-winners
        Linehopper: http://techtalk.parts-express.com/sh...Esoteric-build

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        • #5
          I played around last night with both, and the Omnimic software and XSIM were pretty close to each other. I have to say though, I like doing it in XSIM better. In the Omnimic software you have to continually run the sine sweeps while adjusting the offset until the curves match up. It usually takes me 30-45 secs or more to get it right, and I don't like running the tweeter that long. If people are happy with the XSIM results, I will probably just use that.

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          • #6
            Another thing to keep in mind when setting the "mod delay" offset in XSim is that the W+T "get file" and the W+T "system" file that is entered in the driver tuning dialog box, must both have the same smoothing applied to them. When you load an FRD into XSim using the "get file" option, XSim brings it in using the file"s native resolution. So if you measured it using 1/48th smoothing, then it is imported with 1/48th smoothing.

            The driver tuning dialog box, however, defaults to 1/24th smoothing when importing all FRD's, regardless of the FRD's native resolution. So you have to manually change the smoothing applied from "1/24th" to "none" , otherwise the two curves will not match up properly at the correct "mod delay" offset.
            SideTowers: http://techtalk.parts-express.com/fo...corundum-build
            Totally Flat: http://techtalk.parts-express.com/fo...5-totally-flat
            Plumber's Delight: http://techtalk.parts-express.com/fo...notech-winners
            Linehopper: http://techtalk.parts-express.com/sh...Esoteric-build

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            • #7
              Just to pile on; if you manipulate the FRD files by trimming tails or blending in the near field you need to extract minimum phase then use Xsim with T+W to find the offset.
              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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              • #8
                How do you extract minimum phase? I have heard this, but not sure how to do that. Sent from my SM-G973U using Tapatalk

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                • #9
                  In XSim, you open the driver tuning dialog box and then under "FRD phase source" you will see two buttons: "as measured" which is the native phase data collected by OmniMic, and "derived" which, when you select it, opens another dialog box to extract minimum phase. In this dialog box you put lower and upper tails on the measured curve by adjusting the frequency and slope values. When you have what appears to be "reasonable" looking tails at each end of the curve, you close this dialog box and then a small "H" will appear next to the driver icon on the schematic CAD screen. This small "H" means that you have substituted "Hilbert Transform" data for the native or raw OmniMic phase data (sometimes referred to as quasi-minimum phase data).

                  The only difference between this calculated minimum phase data and OmniMic's quasi-minimum phase data is the starting point at which the measurement begins. Minimum phase data begins or is time referenced to the acoustic center of each driver (somewhere around the face plate or slightly behind the face plate). OmniMic's quasi-minimum phase data begins or is time referenced slightly in front of each driver's face plate. It begins at the peak of the impulse response. So it is slightly delayed compared to minimum phase data.

                  As John mentioned, if you use the blender program to merge near and far field measurements, you then need to extract (or replace) OmniMic's raw phase data with minimum phase data for all files. You cannot mix and match quasi- minimum phase data with conventional minimum phase data because the time markers are slightly different.

                  If this sounds confusing, it is. But the time markers all have to be aligned properly so that the various software packages can sum the curves properly.
                  SideTowers: http://techtalk.parts-express.com/fo...corundum-build
                  Totally Flat: http://techtalk.parts-express.com/fo...5-totally-flat
                  Plumber's Delight: http://techtalk.parts-express.com/fo...notech-winners
                  Linehopper: http://techtalk.parts-express.com/sh...Esoteric-build

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                  • #10
                    Thanks a ton for that info!! Looks like I have some practicing to do. Sent from my SM-G973U using Tapatalk

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