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  • Spitfire Cabinet Design

    I'm excited to build Carmody's Spitfires. However, there doesn't seem to be much detailed information out there as compared to other designs. So I'm unsure how sensitive the sound of this design is to alterations. For a few weeks I will be babysitting a CNC machine in my garage and want to take full advantage. Question is, will the type of baffle alterations being considered in the attached images disrupt their output?

    This is usually a silly question, answer is almost always yes. But perhaps the baffle rounding here is innocuous enough?


  • #2
    The only real "have-to's" is keeping the baffle width the same (+/- 10%), the tweeter at the same location in reference to top and sides and the tweeter's distance from the woofer (center to center distance).
    With that done, you can go crazy...making it taller, deeper and moving the port from front to back or vice-versa and in any finish you want.
    Depending on your likes and dislikes - I would keep the cabinet volume close, or model any changes in cabinet volume, so you can adjust the port accordingly. Paul C. usually goes for a little bump in the bass, which i personally like about his designs, but YMMV.

    Might be missing something - but I don't easily see your "changes" to the baffle.
    Paul

    The "SB's" build page
    http://techtalk.parts-express.com/sh...-4-(pic-heavy)

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    • #3
      You're right, the changes are subtle depending upon angle. The distances you mentioned are indeed maintained. The only difference is that the rounding of the baffle is increasingly biased approaching the center line of the L6-4R, and fades to zero at the top and bottom edges. Examples with this type of rounding probably exist, I just haven't seen them. Makes one wonder whether or not there's a good reason.

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      • #4
        Because it's a pain in the arse for anyone without a CNC :-)

        There are very good acoustic reasons to do massive roundovers--hard edges on the front baffle of a speaker cause jaggedness in tweeter response. It's a type of impedance mismatch. The sound wave travels along the front of the speaker, gets to the edge and all of a sudden encounters open air, causing little response spikes and suck-outs. They're small--rarely more than a dB, but depending on geometry, sometimes the edge effects combine and you get enough that it affects the perceived sound quality.

        Big round-overs on baffles ease that transition, reducing the magnitude of the response abberations. And baffles that have unequal distances from the tweeter to the baffle edge take those ripples and spread them out across the frequency band.

        The baffle you propose would do both things to some extent. It will be theoretically better than a square box. However...probably not a lot more, since your proposed curve is at its greatest by the woofer and not the tweeter. But it certainly isn't going to hurt and it looks wicked cool.
        nothing can stop me now

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        • #5
          BTW, Dynaudio did something similar on their flagship:

          nothing can stop me now

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          • #6
            Originally posted by TheManFromDenver View Post
            You're right, the changes are subtle depending upon angle. The distances you mentioned are indeed maintained. The only difference is that the rounding of the baffle is increasingly biased approaching the center line of the L6-4R, and fades to zero at the top and bottom edges. Examples with this type of rounding probably exist, I just haven't seen them. Makes one wonder whether or not there's a good reason.
            Okay, that's what I thought I was seeing... your explanation confirms it. That's a really unique baffle shape and it's pleasing to the eye, at least mine. It looks different from different angles. It's kind of hard at this point to build something truly different and unique with all the hundreds of MT designs out there, but this one qualifies if you ask me. I'd love to see you build these. Do it, do it, do it!

            TomZ
            *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
            *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

            *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

            Comment


            • #7
              Originally posted by Dirk View Post
              Because it's a pain in the arse for anyone without a CNC :-)

              There are very good acoustic reasons to do massive roundovers--hard edges on the front baffle of a speaker cause jaggedness in tweeter response. It's a type of impedance mismatch. The sound wave travels along the front of the speaker, gets to the edge and all of a sudden encounters open air, causing little response spikes and suck-outs. They're small--rarely more than a dB, but depending on geometry, sometimes the edge effects combine and you get enough that it affects the perceived sound quality.

              Big round-overs on baffles ease that transition, reducing the magnitude of the response abberations. And baffles that have unequal distances from the tweeter to the baffle edge take those ripples and spread them out across the frequency band.

              The baffle you propose would do both things to some extent. It will be theoretically better than a square box. However...probably not a lot more, since your proposed curve is at its greatest by the woofer and not the tweeter. But it certainly isn't going to hurt and it looks wicked cool.


              I find diffraction (edge effects) cause more than simple response jaggedness (amplitude). It also smears transients and other icky things making reproduction even less realistic.
              This design should help but in reality huge radiuses are needed to reduce diffraction, diffraction is also caused by a slew of things other than hard 90 degree corners.

              http://www.aes.org/tmpFiles/elib/20171103/17816.pdf

              Your cabinets can only help and they look awesome! What cnc (toolpath) software are you using?

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              • #8
                Thank you for the feedback. Glad to hear the design shouldn't make Dave Grohl sound like a whining toddler. Must admit that I will probably start with birch instead of $200 worth of dark walnut. Difficult to see how veneering would work out here. Though the more expensive lumber would soon follow. Friends, family, bills..they're all going to be ignored for a few weeks. Will definitely post pictures.

                All the CAD/CAM is in Fusion 360 and it would be easy to post files if there was interest. Fusion is what we use at work with smaller mills, mostly for circuit board creation. Right software, wrong CNC (except for making teeny, tiny little speakers).

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                • #9
                  It seems that one of the prevailing ideas coming out of the recent Iowa DIY event was that we had pretty much solved the problem of driver quality--and their system integration. Any mook with the tools and a little bit of time can build a passable speaker. The literal "state of the art" may be the baffle design.

                  Armed with that--and no CNC, I'm starting to wonder how to do this with other methods. My first thought was a circle jig of sorts, on a *very* large radius, basically just sweeping an arc into the speaker baffle.

                  That, or 3D printed. My build plates max out at 7", so I'd need to print in multiple sections, then assemble, then clean up the surface finish with plasticized Bondo. Maybe fill the back side with epoxy resin. That's a LOT of work, but at least I would never have to route another bloody speaker recess.
                  nothing can stop me now

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                  • #10
                    Great answers, guys. I say build it.
                    Isn't it about time we started answering rhetorical questions?

                    Paul Carmody's DIY Audio Projects
                    Twitter: @undefinition1

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