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  • question regarding textured/rippled/dimpled internal walls

    I notice a trend in several translam and 3d printed DIY enclosure designs to use a textured or dimpled "egg-crate like" inner surface, formed as part of the rigid enclosure material. The stated aim is typically to "break up resonances". I have two questions:
    1. Is there a formal name for it?
    2. Is there any evidence it works?

    I struggle to see how it can work: if the intent is to breakup standing waves, wouldn't the pitch of the pattern and the depth need to be on the same order as the wavelength of the standing wave? (It's typically much smaller.) If the intent is to disperse higher frequencies bouncing around the box, wouldn't the wavelength of interest also need the be small compared to the pitch of the pattern? I can see this maybe being the case for some full range designs, but in most two-ways, the crossover would put the wavelengths within the box well outside the working range of the texture.

    Any thoughts?

    This isn't the best example, but it's what I had to hand, note the ridges on the back surface of the wall of the loading chamber:
    Click image for larger version

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  • #2
    Running this experiment myself now.... https://techtalk.parts-express.com/f...2-build-thread

    The theory is simply that there is no directly reflective surface parallel to each other. Same theory that results in people making speakers from angled sides. If you imagine soundwaves reflecting like light does then a mirror made the same way should give you a decent mental picture of what's being aimed for here.

    I know what your asking though - if the wavelength is bigger wont it pass straight through - isn't the effectiveness of this relative to the size of the wavelength? I guess, maybe?. But sound waves can also be bigger than the thickness of the wall behind your speakers, and yet those waves are reflected back. So if what is reflected back is sent in multiple directions the theory is that it will help dissipate the energy of the reflected wave better than a single reflective surface.

    In any case, its one of those "cant hurt" sort of things. If it doesn't make much of an improvement it certainly wont make it worse.

    Comment


    • zx82net
      zx82net commented
      Editing a comment
      Nice looking project! I concur, the texturing is unlikely to do harm. However, it doesn't exactly come for free, it is all material which could go into making the walls stiffer, rather than just adding "harmless" texture. Of course, material costs matter much less to hobbyists than to commercial builders.

    • DeZZar
      DeZZar commented
      Editing a comment
      Well...it is actually making the walls thicker/stiffer. The minimum wall thickness on any part of this project is 36mm (1.5 inch).

  • #3
    I think you'll find that the "roughness" has to be comparable to the wavelength to do much good. To use your mirror analogy, that's also the situation there. But an experiment never hurts.
    Francis

    Comment


    • #4
      Originally posted by fpitas View Post
      I think you'll find that the "roughness" has to be comparable to the wavelength to do much good..
      True. This is why products that put a textured finish on the inside of cabinets to reduce internal reflections can't do what they claim. In the pictured example the rear chamber should be lined with foam or fibrous damping material to reduce midrange reflections back to the cone exactly as is done with direct radiators.

      The theory is simply that there is no directly reflective surface parallel to each other
      Also true. In the case of the pictured rear loaded horn there's going to be a resonance due to the side walls being parallel. With horn loaded subs you get around this by crossing them over well below the frequency where the parallel walls are 1/2 wavelength apart. With wide bandwidth front loaded horns you just don't have parallel walls. With rear loaders like the one pictured it's unavoidable, as is the response dip where the front and rear waves meet 180 degrees apart. Those factors, along with the total lack of WAF, explain why rear loaders are seldom seen, let alone heard.
      www.billfitzmaurice.com
      www.billfitzmaurice.info/forum

      Comment


      • djg
        djg commented
        Editing a comment
        Clear speaker enclosures sacrifice sound for looks.

    • #5
      Do you guys realize just how awesome the audio reproduction realm of existence could actually be without women?

      :D

      I have.

      Comment


      • djg
        djg commented
        Editing a comment
        Without women there would be no people.

    • #6
      Originally posted by Steve Lee View Post
      Do you guys realize just how awesome the audio reproduction realm of existence could actually be without women?

      :D

      I have.
      True, but.... The existence of humanity doesn't do well without the reproduction realm of women.

      Comment


      • #7
        Marry a musician. A friend did, and she approves of the washing machine sized horn speakers we built. She isn't crazy about the looming presence in the front room, but for a musician the sound trumps vague aesthetics.
        Francis

        Comment


        • Steve Lee
          Steve Lee commented
          Editing a comment
          Best advice yet ^

          :D

      • #8
        I'm unfamiliar with these wife induced limitations. I must have just gotten lucky!! My awesome lady hasn't ever really said no to any stereo setup...if it looks awesome and sounds awesome....auto approved!

        She'll even say things like "...don't you have some speakers to go build or something..."

        Comment


        • #9
          Originally posted by DeZZar View Post
          I'm unfamiliar with these wife induced limitations. I must have just gotten lucky!! My awesome lady hasn't ever really said no to any stereo setup...if it looks awesome and sounds awesome....auto approved!

          She'll even say things like "...don't you have some speakers to go build or something..."

          Lol! I think it comes down to how serious the wife is about music. Most just don't care, as long as the speakers make background noise.
          Francis

          Comment


          • #10
            And are invisible...
            www.billfitzmaurice.com
            www.billfitzmaurice.info/forum

            Comment


            • #11
              Originally posted by billfitzmaurice View Post
              And are invisible...
              Yes, or at least tiny and cutesy. Think Bose Cubes
              Francis

              Comment


            • #12
              Then there's this...


              https://www.autoblog.com/2009/10/22/...-dimpling-mpg/

              Comment


              • fpitas
                fpitas commented
                Editing a comment
                It's the wave of the future! Well, maybe with hardcore golfers ;)

            • #13
              I once asked my wife to evaluate a set of speakers I had recently designed and built. Her method? To walk a circle around one of them while listening.

              dlr
              WinPCD - Windows .NET Passive Crossover Designer

              Dave's Speaker Pages

              Comment


              • wogg
                wogg commented
                Editing a comment
                She was testing off axis power response.
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