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Budget Duelund Three-way

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  • #31
    Greg - how is the project coming along?

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    • #32
      Hi! Thanks for following up.

      I spent last weekend putting a simple black spray paint coat on the sub-baffle and grille. I was uncertain how transparent the grille cloth would be.
      It has also proven tricky using the PE grille attachment knobby things. Lining up both the sub-baffle and grille perfectly so the reveal between the grille and the cabinet edges is consistent and professional looking is a chore.

      My hope this weekend was to be able to take and compare the three measurements that are the naked drivers, with grille frame, and with grille frame and cloth.

      I got my crossover components the other day. I should have enough variety to dial in the target slopes, but we'll have to see.

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      • #33
        Simple black spray paint and grille pics...

        Since the grille is inset and the cabinet is not perfectly square, getting the reveal between the grille and the edge of the cabinet proved tricky. There had to be a gap, and I wanted that gap to be consistent.

        Then, aligning the grille connector knobby things so once attached that reveal is maintained as originally positioned was equally challenging. I ended up drilling the receiver hole large which allowed for a little bit of play. Then I added a dab of epoxy and positioned the grille so it was perfectly centered and let everything dry.
        Attached Files

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        • #34
          The grille cloth attached far easier than I anticipated.
          The staple gun worked, although I had to tap each staple in flush with a hammer.
          Pulling the edges (and corners) in tight worked better than I expected.

          The dental floss is to assist in removing the grilles.
          I never brainstormed a better long term solution to this problem and once I put the grilles on for good it's going to be difficult to get them off.
          I'll probably have to slip a loop of floss under the corner through the reveal, but I'll cross that bridge later.

          Attached Files

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          • #35
            I was able to take the three (3) measurements I alluded to earlier.
            I have personally never seen curves that show clearly what grille cloth does to the FR, so I was very curious.
            All around, I'm happy with how the grille and cloth affect things. Still very manageable for the crossover.

            Cheers!
            Attached Files

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            • #36
              What if you embedded some magnets on the back side of the grill. Then use a hand held magnet from the outside to attract the ones in the grill.

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              • #37
                Back in "the day", it was common for speaker grills to have a little cloth tab on the bottom edge for removing the grill.

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                • #38
                  Originally posted by Billet View Post
                  Back in "the day", it was common for speaker grills to have a little cloth tab on the bottom edge for removing the grill.
                  I did this on a bass cab with a similarly done recessed vintage-y grille. The grille is held on with serious industrial velcro, the loop is just big enough to stick a pen through to get a good handle, the fabric is folded over so it won't tear and it's firmly stapled to the wood grille frame. It's unobtrusive enough that it took me a bit to find it to get the picture.

                  Click image for larger version

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                  • #39
                    Very cool to see the actual effects with real measurements. Thanks!
                    Craig

                    I drive way too fast to worry about cholesterol.

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                    • #40
                      Thanks for the suggestions.
                      The knobby things on the grilles really "snap" into place. I don't think anything weaker than a subwoofer magnet would be strong enough to dislodge them, lol.
                      I did contemplate a pull tab, but then I'd have to make the reveal big enough to fit it...

                      Also, take that upper tweeter measurement with a grain of salt.
                      I successfully overdrove that unit to failure.
                      I don't think the one in the other cab is dead, but I'll have to see. Hopefully I can start prototyping without waiting for replacements to arrive.

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                      • #41
                        I did a pair of Wolf's Zingers in a similar retro style. I bought some PE grill foam but never made grills. Your cabs are very nice. As an older audio enthusiast, I love the picture frame surround on a wood grain cab.

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                        • #42
                          Luckily I hadn't destroyed the tweeter in the other cabinet so crossover prototyping began today!

                          First the woofer.
                          A nearfield mic was able verify the target slope.

                          Click image for larger version

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                          I have real issues with the crossover values in my models versus what ends up measuring appropriately. This isn't the first time either. It always manages to humble me.
                          My model called for a 4.0 mH coil with a "tank" bottomless notch using a 0.17 uF cap. On the shunt circuit my model called for a 80 uF cap with a 3 ohm resistor to relax the rolloff a little and adjust the phase for good integration with the midrange.

                          The slope above ends up using a 3.0 mH coil with a 0.17 uF "tank" value, and a 100 uF cap with a 3 ohm resistor.

                          All in all though, the Duelund slopes are achievable with simple second order electrical filters. A Duelund slope really only deviates from a LR2 pretty far down the rolloff where it starts to approach LR4.

                          I did play around with the "tank" cap value to see how critical it is to use 0.17 uF, because I couldn't find a single cap with a value close enough.
                          Unfortunately it does make a difference, because to achieve 0.17 uF (0.165 uF), two (2) 0.33 uF caps need to be wired in series.
                          The comparison below shows that both 0.1 uF and 0.2 uF attenuate the woofer breakup around 5 dB less than nailing it with the right value.

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                          I have not conducted any sort of listening test to determine if it matters or not. It's entirely possible it's inaudible. Using a 0.1 uF value or 0.2 uF value also affects the rest of the crossover negligibly- it does not affect the phase at all so integration with the rest of the system is unaffected.
                          Attached Files

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                          • #43
                            The midrange similarly is able to hit the Duelund slopes with second order electrical filters on both the high pass and low pass side.

                            Click image for larger version

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                            The high pass matched my model exactly. A 68 uF cap with a 1.8 mH shunt.
                            The low pass deviated slightly. I had modeled 0.6 mH and a 8.0 cap. I had to adjust the inductor to 0.4 mH here.

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                            • #44
                              Measuring the tweeter uncovered some more unforeseen problems.

                              The most important is that I only ran three (3) wires internally for the midrange and tweeter, thinking one common ground should allow me to prototype each respective driver.
                              After sleeping on it, it dawned on me that with the midrange wired in reverse polarity, each driver's circuit doesn't go straight to ground without a component in there, so it is effectively impossible to wire both up using only three wires with the crossover external... I feel silly for overlooking this. I will need to run another ground wire internally in order to continue.

                              However, I was able to measure just the tweeter.

                              Click image for larger version

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                              A 6.2 uF cap with a 0.30 mH inductor matched my model pretty well. This cabinet's grille has some imperfections I believe that are leading to the peak-dip combo seen at 6.5 - 7.5 kHz.

                              Exactly how the phase meshes between the midrange and the tweeter will likely result in these values being adjusted and deviating from the target slopes. Although I measured the acoustic center difference between the drivers, I don't trust my model to predict a nice deep reverse null without some empirical tweaking.

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                              • #45
                                That grill is positioned proud of the front baffle? There's a gap under it, that is?

                                dlr
                                WinPCD - Windows .NET Passive Crossover Designer

                                Dave's Speaker Pages

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