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Speedster with slanted baffle and sides?

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  • Speedster with slanted baffle and sides?

    Hi everyone,

    I have an idea to build a small high quality 2-way bookshelf speaker in either concrete or somekind of resin (e.g. epoxy granite). My idea is to make a mold that can be reused by having two molds that fit into each other where the bottom of the mold is “open” this is where the mix is poured in (upside down).

    In order for the cabinet to release from the mould I need the four sides of the speaker to be slightly slanted towards the top. Having slanted sides should be an advantage due to acoustic center alignment on the baffle as well as help to eliminate internal standing waves as the sides are no longer parallel. However, I’m not sure how these changes affect the frequency response and if I need to take this into account in the crossover design.

    I’ve previous built Jeff Bagby’s Piccolos as well as Paul Carmody’s Overnight Sensations. I like the idea of using another proven design for this build and I got my eyes on Paul Carmody’s Speedster. My question is whether it would make sense to keep the original crossover in my design? I have attached a quick 3D rendering of what I have in mind. I have kept the horizontal distance from the center of the tweeter to the sides the same as the original design. All sides including the baffle and backside have a 4 degree slant towards the top. Baffle height is the same as the original Speedster, the walls are 20mm thick, and I have extended the depth of the speaker to keep a 5.5 liters internal volume.

    So my questions are:
    1. Will the change in baffle design require a new crossover design?
    2. Will the slanted baffle / acoustic offset require a new crossover design?
    Thanks a lot!
    Last edited by Soren; 02-05-2018, 02:14 PM.

  • #2
    1) Yes, depending on the difference of your dimensions vs original
    2) Yes, as driver time alignment will change depending on your baffle's angle

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    • #3
      I know the theoretical answer to both my questions is YES as you correctly pointed out, but since my design only differs slightly from the original Speedster, I was wondering if I need to change the crossover design or if it would be okay to keep it as is? Attached is s picture showing the front and side view difference between the original Speedster and my design. It's a 4 degree angle on both the sides and baffle.
      Last edited by Soren; 02-06-2018, 07:52 AM.

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      • #4
        Just make the mold in pieces so it can be disassembled.

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        • #5
          Thanks for the suggestion, but my intention was to avoid making the mold in pieces. Also, I kind of like the looks of the slightly slanted baffle and sides, and considering it only differs very little from the original design, I was hoping I could go ahead with it and use the original XO.

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          • #6
            A dimensional variance of +-10% will not be audible at all with the original crossover.
            The room and position of the speaker will have much more effect on the sound (on a desk, shelf, stand etc.).
            Go for it!

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            • #7
              And even if it was "slightly" audible, you probably have to do it anyways...because those slanted sides are sooo sweet!

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              • #8
                Thanks for the encouragement
                I will start making a mold for just the baffle and test different concrete mixes for strength and finish.
                Last edited by Soren; 02-06-2018, 09:43 AM.

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                • #9
                  Originally posted by Soren View Post
                  Thanks for the encouragement
                  I will start making a mold for just the baffle and test different concrete mixes for strength and finish.
                  You probably want to use cement, not concrete
                  Play with adding fibers to the mix for strength and something like little Styrofoam balls for lighter weight.
                  I think there is a thread or two about cement enclosures at diyaudio forum

                  I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
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                  • #10
                    You might want to look into Stucco. I believe it already comes with fibers in the mix for strength. And don't forget coloring agents.
                    Last edited by Millstonemike; 02-06-2018, 04:04 PM.

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                    • #11
                      I like the idea. As long as the angle isn't too steep, I don't think it should be a problem. Basically, all you're doing is tiling the listening axis up a bit.
                      Isn't it about time we started answering rhetorical questions?

                      Paul Carmody's DIY Audio Projects
                      Twitter: @undefinition1

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                      • #12
                        Originally posted by Millstonemike View Post
                        You might want to look into Stucco. I believe it already comes with fibers in the mix for strength. And don't forget coloring agents.
                        I think the names vary depending on the country. I read through some Danish forums about "concrete" speaker building based on the legendary Steen Duelund who made some horn speakers in cement/concrete. Apparently he used a mix of cement, sand, and plaster, which is actually what "stucco" consists of according to Wikipedia.

                        Today I bought a bag of premixed cement and sand that just needs water to make concrete. This was what the guy in the store suggested me to use. I asked about fibers, but he said he wouldn't use it for this application. I also got a bag of plaster and a bottle of plasticizer. I will make some different mixes and test for strength and looks.

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                        • #13
                          Originally posted by Paul Carmody View Post
                          I like the idea. As long as the angle isn't too steep, I don't think it should be a problem. Basically, all you're doing is tiling the listening axis up a bit.
                          Glad to hear it from the designer himself What's your opinion on the angled sides? Am I doing it right when keeping the horizontal distance from the center of the tweeter to the sides the same as the original Speedster?

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                          • #14
                            Originally posted by Soren View Post

                            I think the names vary depending on the country. I read through some Danish forums about "concrete" speaker building based on the legendary Steen Duelund who made some horn speakers in cement/concrete. Apparently he used a mix of cement, sand, and plaster, which is actually what "stucco" consists of according to Wikipedia.

                            Today I bought a bag of premixed cement and sand that just needs water to make concrete. This was what the guy in the store suggested me to use. I asked about fibers, but he said he wouldn't use it for this application. I also got a bag of plaster and a bottle of plasticizer. I will make some different mixes and test for strength and looks.
                            Remember, the less water used in the mix the stronger the final product. That's why "paver" blocks are so much stronger than a poured concrete slab. The pavers are made in a factory; the cement forced into molds.

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                            • #15
                              I made some concrete speedsters once

                              http://techtalk.parts-express.com/fo...3d-print-build

                              Do you intend to flush mount the tweeter?
                              // WWW.JONCON.NET

                              // SPEEDSTERS - Concrete over 3D Print Build Thread

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