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Symmetro: a proof-of-concept

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  • Symmetro: a proof-of-concept

    Thought I'd share a project Derek (deschu) and myself are working on. This started with my experience that despite the technical shortcomings of the MTM, I often really like their sound, better than an identical TM at times. I'm not the only one and I think the assumption is that there is reduced sound power - especially vertically - around the crossover, which is typically a region sensitive to the ears. I also know that I hate low ceilings for good sound. After the wall behind the speaker, the ceiling seems - to me - the next worst offender. So I started thinking about how I could control vertical dispersion, while maintaining - or even increasing - horizontal dispersion compared to a typical speaker. I'd already had an idea for the layout, either MMTMM or WMTMW, with the proper driver spacing vs crossover to constrain the vertical dispersion. But the mids must be tiny to get close enough so they're vertical dispersion is constrained, but not so much that it was very different from the rest of the speaker response. When I started working with the Tectonic Elements 46mm BMR in a soundbar project and an AMT in a dipole, the final concept clicked.

    For the conceptual modeling you will notice that the vertical dispersion is quite constrained in the window where ceiling/floor bounce matter. Constrained and even. The mid/tweet crossover region- expected to be the worst - is constrained but also bigger than say a typical MTM. In addition above and below that is also constrained, so that what does get reflected will at least be a smoother response than say, a lot midrange/bass energy bouncing up or down, then suddenly a laser beam in the mid/treble area, and then back to treble spraying everywhere. Here is the polar response from 500hz-4500hz of a typical 2-way TM:


    And a typical 3-way TMW:


    And this is Symmetro:



    Last edited by augerpro; 01-24-2017, 07:11 PM.
    ~Brandon

    Soma Sonus
    DriverVault

  • #2
    And actually when I did those plots, I had forgot to add realistic acoustic centers in the typical examples, so they would actually be a bit worse through the crossover (the smallest lobes) than depicted.
    ~Brandon

    Soma Sonus
    DriverVault

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    • #3
      Brandon,
      Looks interesting and (sort-of) effective, but at most listening distances in rooms I've had available, the energy at about 50 or 60degrees vertical off-axis is what would reflect off the ceiling and reach the listening chair. That looks to be not so far down and with erratic response there. Any chance to steer that null toward wider angles?
      Free & Free-form simulator/designer for Passive Crossovers
      SynergyCalc 5: design spreadsheet for Wooden horns and DIY Synergy Waveguides
      Super easy and cheap to make high performance sound diffusers

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      • #4
        I did a bunch of geometry looking at exactly that. 25-45 degrees were actually the most problematic angles. Bases on my assumptions anyway (9ft ceiling height, 12-16ft listening distance)
        ~Brandon

        Soma Sonus
        DriverVault

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        • #5
          I also looked at extending this concept to a low cost version using the TangBand W5-704D woofer and Beston RT001A.
          ~Brandon

          Soma Sonus
          DriverVault

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          • #6
            All I see is the cabinet photo. Based on the discussion there should be some charts and graphs, correct?
            "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
            exactly a Fc 3K for both drivers, anybody can do it." -Xmax

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            • #7
              I had vertical polars and a description of the design aim, but that's pretty dry reading and people don't seem to interested in that.
              ~Brandon

              Soma Sonus
              DriverVault

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              • #8
                Why would technical discussion be "too much information" on a discussion forum dedicated to designing and building speakers? Isn't that exactly the point of the entire forum?

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                • #9
                  *shrug* Just my perception. Anyway I edited the first post as it originally was.

                  For Bill:


                  ~Brandon

                  Soma Sonus
                  DriverVault

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                  • #10
                    I've received the cabinets and measurements are imminent! I'm always impressed with these Esoteric drivers, just a great design. I pasted together the distortion plots of the drivers in their respective passbands also.

                    Kieth E if you are reading, once I get measurements I'll be putting the BMR's back in the soundbar and finish voicing.


                    ~Brandon

                    Soma Sonus
                    DriverVault

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                    • #11
                      Originally posted by augerpro View Post
                      I've received the cabinets and measurements are imminent! I'm always impressed with these Esoteric drivers, just a great design. I pasted together the distortion plots of the drivers in their respective passbands also.

                      Kieth E if you are reading, once I get measurements I'll be putting the BMR's back in the soundbar and finish voicing.

                      Haha... I just happened to check this post to see what you were up to these days. Looks really neat! I've been pretty darn busy myself, but if you happen to get a passive XO design together for the soundbar, that'd be swell too ;) I'm assuming those pics are in your new place? I know you had a lot of work going on to remodel parts of the property. If this is any indication, that work must have finished well!
                      Last edited by KEtheredge87; 11-27-2018, 03:22 PM. Reason: Didn't need to re-share the photos.
                      Voxel Down Firing with Dayton SA70
                      Translam Subwoofers - The Jedi Mind Tricks
                      The Super Bees - Garage 2 way
                      SevenSixTwo - InDIYana 2018 Coax

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                      • #12
                        Yeah it has been a long year, but the main floor is 95% done. Just some crown molding and base board trim to finish. You know, if it wasn't for speaker building, I probably wouldn't have the tools or skills to have taken this remodel on!
                        ~Brandon

                        Soma Sonus
                        DriverVault

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                        • #13
                          Is the font baffle simply screwed on? (any gasketing ?)

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                          • #14
                            Nominal design is screwed on with cabinet screws to inserts, with gasketing.
                            --Derek

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