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Understanding the behavior of a conical cabinet.

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  • Understanding the behavior of a conical cabinet.

    I'm thinking of making a conical enclosure, mainly for aesthetic reasons, but I'd like to understand the acoustic impact too. It will be a conical volume with a length to diameter ratio of probably between 3:1 and 6:1.
    People sometimes call a long conical enclosure like this a transmission line, (e.g. B&W nautilus), which confuses me slightly, because they don't seem to have the properties of a transmission line. Here's my crude thinking:
    With a closed cone, which tapers down to nothing, no energy escapes from the closed end, and there is no reflection from the closed end, because it is infinitesimally small. Effectively, there is no interaction between the tip of the conical volume and the driver, so the length of the conical chamber doesn't matter. It shouldn't be thought of as a transmission line, best to treat it as a sealed box which can't form standing waves. How outrageously wrong am I?

    Insight will be graciously received.

  • #2
    What about the base of the cone? What shape is it?

    Comment


    • zx82net
      zx82net commented
      Editing a comment
      A circle. With the driver mounted in the flat face

    • Steve Lee
      Steve Lee commented
      Editing a comment
      This is a great question!

  • #3
    Here --> http://techtalk.parts-express.com/fo...aker-enclosure

    Looks like it has been covered before . . . but not in any depth . . .

    Comment


    • zx82net
      zx82net commented
      Editing a comment
      Thanks, I'll review

  • #4
    Build one and see.

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    • #5
      The advantage to a conical cabinet in the B&W fashion is reduction of internal reflection sourced response zits, because there are no parallel walls and no constant cross section. Being conical doesn't make it a transmission line, although a transmission line may be conical.
      www.billfitzmaurice.com
      www.billfitzmaurice.info/forum

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      • #6
        And as Olson showed, a driver in the end of a cylinder is the worst possible configuration. Like all baffles, radius the edge does wonders.

        The advantage for the B&W is sales bling and support to their profit margin. . The rest of us get buy with a well stuffed chamber.

        Comment


        • #7
          IIRC someone at diyaudio.com did something like this but added variable rates of stuffing down the length of the cone. It seems to work well based on his findings. Again IIRC he used such a structure inside a conventional cabinet, so there's no disagreement with Olsen ;-)

          Comment


          • Steve Lee
            Steve Lee commented
            Editing a comment
            Yup - a cone for a mid inside a cabinet would be about perfect and help with internal box reflections for the woofer in the same box . . .

        • #8
          Originally posted by billfitzmaurice View Post
          The advantage to a conical cabinet in the B&W fashion is reduction of internal reflection sourced response zits, because there are no parallel walls and no constant cross section. Being conical doesn't make it a transmission line, although a transmission line may be conical.
          Yep, that was what I was thinking,
          So in conclusion: Cone length does not need to be tuned to driver parameters. Instead, for a given volume of cone, it is probably best to determine the diameter-to-length aspect ratio based on baffle constraints. Sound reasonable?

          Follow on question: when it comes to minimizing baffle diffraction, any thoughts on what the ideal end profile is. I've called two options a toroidal-cap and a spherical cap, crude sketch of the cross-sections:
          Click image for larger version

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          Attached Files

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          • #9
            The modelled BaffleStep effect from a flat/circular face looks very similar to a square baffle with edge-to-edge dimensions the same as the circle's diameter....so I'm not sure the flat circular shape is worth the trouble compared to a square-base pyramid on its side.

            If you're thinking about a circular front (like a full radius roundover), then it smooths out the ~2db bump that comes after/above the BaffleStep, but that's about it, so likewise probably not worth the trouble if you're mostly interesting in BSC if you can deal with it in the XO instead....Unless you're doing it for asthetic purpose.
            My first 2way build

            Comment


            • #10
              Originally posted by LOUT View Post
              The modelled BaffleStep effect from a flat/circular face looks very similar to a square baffle with edge-to-edge dimensions the same as the circle's diameter....so I'm not sure the flat circular shape is worth the trouble compared to a square-base pyramid on its side.

              If you're thinking about a circular front (like a full radius roundover), then it smooths out the ~2db bump that comes after/above the BaffleStep, but that's about it, so likewise probably not worth the trouble if you're mostly interesting in BSC if you can deal with it in the XO instead....Unless you're doing it for asthetic purpose.
              I'll be printing it or printing and casting it, so the circular and spherical shapes come at no cost. In fact, they are probably cheaper since they'll be more material efficient!

              Comment


              • #11
                Originally posted by zx82net View Post
                So in conclusion: Cone length does not need to be tuned to driver parameters. Instead, for a given volume of cone, it is probably best to determine the diameter-to-length aspect ratio based on baffle constraints. Sound reasonable?
                Yep. You'd chose a baffle dimension and the cone length would be whatever was required for the desired box volume. The difference between a rounded cone or a segmented cone would be minimal other than rounded be the most resistant to vibration.

                www.billfitzmaurice.com
                www.billfitzmaurice.info/forum

                Comment


                • #12
                  Would these be suitable for a mid driver in a traditional box enclosure?

                  https://www.amazon.com/REEHUT-Plasti...152606&sr=8-13

                  Comment


                  • #13
                    Originally posted by Steve Lee View Post
                    Would these be suitable for a mid driver in a traditional box enclosure?

                    https://www.amazon.com/REEHUT-Plasti...152606&sr=8-13
                    In my experience, those kind of cones, are made of something very tough, but with low rigidity, like low-density polyethylene, or polypropylene. I think there is a chance they could transmit significant pressure from the woofer. It you are looking for pre-made enclosures, you might be better looking for something in ABS, polycarbonate, or melamine. Perhaps some kitchenware. Melamine it really pretty stiff but has quite a dead sound to it, a bit like wood, might be worth looking into.

                    Comment


                    • #14
                      Good perspective.

                      I'll look into stiffer cones in my future searches - I just know that there is something suitable out there with far less cabinet cabinet volume robbing mass than making pyramids from wood.

                      Comment


                      • #15
                        Originally posted by Steve Lee View Post
                        Would these be suitable for a mid driver in a traditional box enclosure?

                        https://www.amazon.com/REEHUT-Plasti...152606&sr=8-13
                        Cover that cone in a couple of layers of fibreglass and you may have something. Or do the layup internally and remove the cone after to reveal a smooth paintable surface if it is going to be exposed.

                        Stack one cone inside another with something like a 3/4" spacer at the flanges, fill the resultant gap between them with a mortar mix and you have something very intriguing..

                        Comment


                        • LIDAR
                          LIDAR commented
                          Editing a comment
                          You're on to something there Dukk. However you might not want all that weight, so maybe a much thinner spacer and some pourable epoxy.

                        • Steve Lee
                          Steve Lee commented
                          Editing a comment
                          I'm trying to figure out just how thick the cone material needs to be. If it is rigid and stuffed with fiberfill I suspect it doesn't need to be thick - just stiff/rigid?
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