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Requesting advice for a 3D Printed Voxel Remix

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  • Requesting advice for a 3D Printed Voxel Remix

    I'm designing a subwoofer intended for 3D Printing, based on Paul Carmody's Voxel design. To make the design accessible, I'm targeting a 180x180x180mm build volume, which rules out using the same dimensions, but the same internal volume can be achieved in 2 sections for the main enclosure. I'm pretty much a novice when it comes to acoustic design, so I'd appreciate some feedback before I finalize the design. I've come up with a construction that precisely matches the internal volume, the port length and diameter, and as best as I can tell, the port flare radius. It's basically a square section tube printed in two parts that glue together, re-enforced by bolts. There are three shelf braces along the length and the walls are 10mm thick. The front and rear baffles glue into place and are 12mm thick. Due to the constraints on the dimensions, the port is directly behind the driver, but there is ~55mm of clearance between the flared end and the magnet. I've attached some section diagrams from the CAD. (I realize the section of the shelf braces may look a bit odd, that is so they can print without supports.) Any thoughts?

    Luke

    edit: The CAD isn't finalized, obviously, the driver will not actually be held by the outside edge!

  • #2
    The 10mm walls seem a bit thin, especially if the material is a plastic. May not matter a lot, though.
    Francis

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    • #3
      Thanks Francis. The model is parameterized, so the wall thickness can be changed with a number, and I can produce multiple models. There's obviously a trade-off with the cost of plastic. With reasonable infill and 10mm walls, the whole enclosure will probably be ~ 2kg, putting the cost of plastic at around 1.5x the cost of the driver, which I'm guessing is probably acceptable for most hobbyists. What I do know from experience is that the mechanical resonance modes in the walls should be well into the 100's of Hz. I believe that should be ok for a subwoofer, shouldn't it?

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      • #4
        Originally posted by zx82net View Post
        Thanks Francis. The model is parameterized, so the wall thickness can be changed with a number, and I can produce multiple models. There's obviously a trade-off with the cost of plastic. With reasonable infill and 10mm walls, the whole enclosure will probably be ~ 2kg, putting the cost of plastic at around 1.5x the cost of the driver, which I'm guessing is probably acceptable for most hobbyists. What I do know from experience is that the mechanical resonance modes in the walls should be well into the 100's of Hz. I believe that should be ok for a subwoofer, shouldn't it?
        Yes, just considering the resonant frequencies. Although there are those who worry that the walls will be excited at harmonics of the driving tone, and at the harmonics emitted from the driver. But I was mainly thinking about flexure, and loosing bass because of that. Still, I guess the user will just turn it up a bit more
        Francis

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        • #5
          Ok, got you. I could go to a circular cross section, but I'd need to go to 3 body parts to get the enclosure volume using my target print volume. If this is used on its side, the driver is likely to be very close to floor level, is that any issue acoustically? (I'll design an optional grill to protect the driver, so there shouldn't be a problem with kicking it!)

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          • #6
            I was playing with the idea of putting the port on the front face, but it would need to be non-circular to accommodate a significant flare, and it's very close to the edge of the baffle. I was concerned it might exacerbate chuffing.

            (Note: This image is for a 200x200mm foot-print, not 180x180 like the design above.)

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            • #7
              Originally posted by zx82net View Post
              Ok, got you. I could go to a circular cross section, but I'd need to go to 3 body parts to get the enclosure volume using my target print volume. If this is used on its side, the driver is likely to be very close to floor level, is that any issue acoustically? (I'll design an optional grill to protect the driver, so there shouldn't be a problem with kicking it!)
              Sub drivers very often are near the floor. That's no problem, in fact it's a good place for them. My problem with your front port is the lack of serious flare. As we know from countless memes, flare does matter!
              Francis

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              • #8
                Yeah, I'm pretty set with the port on the back. The only thing that's bugging me is if someone wants to use it vertically with the driver pointing down, the port's open to collecting debris. I've seen this kind of "plug" proposed in a paper, but I don't think I've ever seen it implemented. I could make that kind of conical feature and extend the "flange" across the entire back face, but it feels like a bit of a hack.
                Attached Files

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                • #9
                  I could implement it something like this, by making the hexagonal grille solid, and placing the conical feature above the port.
                  Attached Files

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                  • #10
                    Alternately you could make the port down-firing, my personal favorite. You would need to have legs or a stand, or other spacers from the floor to allow the port to breath. The driver would point upwards then, but that doesn't seem like a problem.
                    Francis

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                    • #11
                      Good point!

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                      • #12
                        I have a follow on question. I'd like to make a version of the port with adjustable length, at least initially, to assist in tuning. I'll probably do that by making multiple center sections for a 3-part port, with different lengths. What would make a sensible range and granularity? I was thinking maybe +/-2cm in 1cm increments. Is that too fine, would I be better off with a larger range of adjustment?

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                        • #13
                          Hard to tell, really. It's going to at least partly depend on the driver T/S parameters and how close they are to published. +/-2cm seems like a good start though. I usually start with the port a bit long, maybe by 1.5cm, then measure and trim accordingly. After the right length is achieved I glue everything securely.
                          Francis

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                          • #14
                            I think if you have the port and volume exactly like Paul's Voxel you should be fine, as lots of people have built the Voxel and been happy.
                            The thing I would be worried about in your pics of post #1 is the port right behind the driver. BUT, depending on how much space there is between the driver and port plus the large flare it may not matter.

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                            • #15
                              looking good -- a perfect match for the BMR satellites. a really nice 2.1 system

                              note that the 1.5" port in the original voxel subwoofer definitely chuffs at higher volumes, even with flared ends.

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