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First Design Project: Desktop 2 Way

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  • First Design Project: Desktop 2 Way

    Hi folks,
    l've been on holidays for a little while now and facing another few weeks of self-isolation and working from home.
    I thought this would be a perfect opportunity to start a project more or less from scratch and learn some of the basics of speaker design, which I would like to get much much better at, with others' help I hope .
    I've built several kits/existing designs and have built several fairly high end car audio systems but have never designed my own speakers.

    I've got a DATS V2 as well as omnimiv V2 , which I used to take FRD and ZMA measurements of the drivers I'm thinking of using:

    Peerless HDS 821882 5 1/4" mid
    SB Acoustics SB29 RDC Tweeter

    The drivers were mounted on the end enclosures, about .35 cubes. measurements were taken with omnimic 16" away (adjusted on PCD accordingly) at tweeter level maintaining positions and levels per Jeff Bagby's instructions on finding Z offset.
    I've gotten as far as estimating the Z offset to be -0.025 m however the summed curve and imported overlay curve aren't matching very well in PCD on the mid range (pic added below as the forum does not allow uploading xlsm files?).
    Not sure where to go from here... any help would be appreciated

    thanks,
    Marco

    Click image for larger version

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    Attached Files

  • #2
    I'd start with the woofer. Set a target response in PCD, and try to match it. Go ahead, and speculate on how much baffle step compensation you want. The offset is not critical, unless you expect the sim to be perfect, and hope to have a perfect xo without any additional tweaking. I do many x-overs by trial and error, but I have parts on hand. Never measured an offset even once.

    Do you have any x-over parts?

    Can you post a picture of the woofer response, and possibly a picture of your measurement setup?

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    • #3
      Did you (can you) try reversing the tweeter polarity in your (summing) sim?

      Comment


      • #4
        Like this. (Note.... wrong zma file )

        Click image for larger version

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        • #5
          Ever use XSim to model crossovers?
          http://techtalk.parts-express.com/fo...khanspires-but
          http://techtalk.parts-express.com/fo...pico-neo-build
          http://techtalk.parts-express.com/fo...ensation-build

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          • #6
            Guys! Come on! He is still looking at finding the correct offset.

            Adjust the woofer Z axis til it matches the overlay. At that distance, you might end up around -0.035 or more
            https://www.facebook.com/Mosaic-Audi...7373763888294/

            Comment


            • #7
              Originally posted by Kornbread View Post
              Ever use XSim to model crossovers?
              No, I've only used PCD. The filter I posted is a traditional 4th order with a couple of added resistors on the capacitor legs. The Impedance file is one of mine. The ones posted by the OP are for the tweeter.

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              • #8
                Originally posted by isaeagle4031 View Post
                Guys! Come on! He is still looking at finding the correct offset.

                Adjust the woofer Z axis til it matches the overlay. At that distance, you might end up around -0.035 or more
                Well, I hope he's not still wasting time on that.

                Comment


                • #9
                  Originally posted by rpb View Post

                  Well, I hope he's not still wasting time on that.
                  Not wasting time on what?
                  https://www.facebook.com/Mosaic-Audi...7373763888294/

                  Comment


                  • #10
                    Originally posted by rpb View Post
                    I'd start with the woofer. Set a target response in PCD, and try to match it. Go ahead, and speculate on how much baffle step compensation you want. The offset is not critical, unless you expect the sim to be perfect, and hope to have a perfect xo without any additional tweaking. I do many x-overs by trial and error, but I have parts on hand. Never measured an offset even once.

                    Do you have any x-over parts?

                    Can you post a picture of the woofer response, and possibly a picture of your measurement setup?
                    The offset isn't critical? Please tell me you are kidding? The acoustic offset is important for knowing the time of flight and phase difference at the crossover point. Why bother using a sim if you are not going to use it properly.
                    https://www.facebook.com/Mosaic-Audi...7373763888294/

                    Comment


                    • #11
                      Originally posted by isaeagle4031 View Post

                      The offset isn't critical? Please tell me you are kidding? The acoustic offset is important for knowing the time of flight and phase difference at the crossover point. Why bother using a sim if you are not going to use it properly.
                      The offset would affect where the nulls are, and very little more. Using a reasonable estimate is more expedient than spending 2 days trying to pin it down closely, when in the end, the OP will change a cap, or coil value to tweak the response anyway. If the OP ever gets a good looking sim from these measurements, he can alter the offset in the sim, and observe the potential changes from an error in his offset estimate. He might then add extra parts to his xo order. He can tweak the controls in PCD to see what the response might look like 15 degrees above the design axis. It appears to me that his baffle is a diffraction nightmare, and the title of the thread suggests that the speakers will sit on a desk. Due to diffraction, his actual measurements 15 degrees above or below the axis are likely to have wild swings anyway. I mean really, how much worse can it get, and you are still worried about the offset estimate? Please tell me you're kidding. He's got about 14 days to make a usable x-over, and unlike 90% of threads like this, he can measure the results, and fix anything that's not to his liking. On top of all that, It took me 6 parts for the woofer portion of the filter due to the baffle, or possibly due to poor measurement technique. The OP will probably decide the cost of the xo is too high, and scrap the whole project. That alone would also make finding the exact offset irrelevant, and a waste of time. I mean, how often does a novice want a maximum of 4 or 5 xo parts, and think that anything more is unnecessary? Did you look at the tweeter response? I didn't even bother trying to sim a filter for the tweeter. If these speakers sit on a desktop, and the OP is not napping, his ears will be above the normal tweeter axis. He might want to tilt the speakers to account for this, which would also make the sim offset pretty much irrelevant.

                      To the OP.... If you want to learn, I'd suggest designing this as if it's a stand mounted monitor. I'd improve the baffle, and take new measurements.

                      Comment


                      • #12
                        I am not in the mood to really argue with you today. I will add this however. The more accurate the sim, the more predictable the results.

                        OP, There is an error with your woofer zma file.
                        If possible, I would retest with the tweeter level at 90db If this is going to primarly sit on a bookshelf or desk, I would take your measurements in that location. This way the baffle diffraction is accounted for.
                        https://www.facebook.com/Mosaic-Audi...7373763888294/

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