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Metamaterial Absorption Technology

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  • #46
    Originally posted by billfitzmaurice View Post
    In the simplest of terms it refers to a non-naturally occurring composite. That makes the KEF doo-dad a muti-frequency Helmholtz resonator constructed from a composite material. ]
    Yes, Bill, you and tvrgeek had the eye to spot right away how the KEF device works. It is a bank of resonators.

    One reason to dislike the word "metamaterial" and to blame KEF for marketing hoo-ha by retaining that specialized term, is that it mystifies. It makes their device appear to be a new space-age material, like teflon, when it is actually an application of a principle as old as the flute. Pan pipes and pipe organs and brass quintets are all broadband acoustic resonator arrays, and we don't call any of them a "metamaterial." What is new about it is not the material, or the science, but the application (damping sound, such as inside a tweeter rear chamber).

    Another reason to dislike the word is that it almost guarantees a misunderstanding--that it is about what the device is made of. The concept of a metamaterial is that it is a structure that can be substituted in applications that would normally use a porous material to absorb sound by impeding it. Using the porous material, whether natural (wool, cotton) or non-natural (fiberglass, polyester), requires paying attention to which material one is using. When using a metamaterial, in contrast, what it is made of is immaterial. KEF's device is injection-molded plastic (non-natural), but it could also be implemented by casting gold or carving out of maple (both natural). What makes it a metamaterial is that KEF is using it to replace the fibrous lining, or wad of stuffing, they might have used to kill the tweeter's rear wave in a conventionally-shaped chamber.

    If we can speak of using a quadratic diffuser to "absorb" the sound in a room, then it counts as a metamaterial, because it substitutes for a similarly sized and shaped panel filled with porous absorbing material, such as fiberglass. The diffuser can be made of wood or bamboo or cobble stones (natural) or MDF or plastic or dehydrated Twinkies (non-natural), it doesn't matter.

    The only reason the Nautilus tweeter rear chamber would not also be called a metamaterial is that the exponential-horn solution is less like swapping one lining or stuffing for another than it is a whole different rear chamber. This seems wrong to me. A category error. Whatever kind of thing a Nautilus tweeter chamber is, this KEF Meta chamber is, also. KEF is not just lining a box with a new kind of material; they are building an enclosure with a particular kind of labyrinthine structure.

    We are bound to hear a lot of chatter about metamaterial, and it will contain much confusion. Because KEF invented a device amounting to an enclosure design and gave it a name that makes people think it is a material.

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    • #47
      "Now with Metamarketing!"

      "It could be made with materials reverse engineered from crashed alien space ships. We're not saying."

      Steve Guttenberg seems like a really nice guy, and his enthusiasm is infectious, but in the little time I've paid attention to him he has said and written some things that make it obvious he has no clue about physics. That's no crime, of course, but man some of the things he comes up with...

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      • #48
        Originally posted by fpitas View Post

        Why bother? It features a coaxial horn tweeter. I have it on good authority that horns sound like crap.
        Maybe why the Q1 had such a ragged top end. I DID own a pair.

        I would call it a wave guide, not a horn, but augmentable. At least it has no diffraction generators ( section dividers) or sharp exit edge.
        Hearing is believing and no one here has heard them.

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        • #49
          Originally posted by tvrgeek View Post

          Maybe why the Q1 had such a ragged top end. I DID own a pair.

          I would call it a wave guide, not a horn, but augmentable. At least it has no diffraction generators ( section dividers) or sharp exit edge.
          Hearing is believing and no one here has heard them.
          Yet never having heard many horn systems, you are more than eager to damn them all. There's some big hypocrisy brewing here.
          Francis

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          • #50
            Francis,
            You said what horns you have. The old Altec with old drivers. I have heard them in other applications. I stand by my conclusion. I have never heard a horn speaker that did not sound ragged. I have heard a lot, but of course not all. You like them, I do not. Ragged response and poor imaging from every one I have ever heard. I would have liked to hear an NA12 but as the good Dr. has retired, not likely. He used a modern B&C driver, eliminated the diffraction problems, and the foam plug claims to resolve the major resonance issues, His plots suggest success. I'll never know.

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            • #51
              Originally posted by tvrgeek View Post
              Francis,
              You said what horns you have. The old Altec with old drivers. I have heard them in other applications. I stand by my conclusion. I have never heard a horn speaker that did not sound ragged. I have heard a lot, but of course not all. You like them, I do not. Ragged response and poor imaging from every one I have ever heard. I would have liked to hear an NA12 but as the good Dr. has retired, not likely. He used a modern B&C driver, eliminated the diffraction problems, and the foam plug claims to resolve the major resonance issues, His plots suggest success. I'll never know.
              I don't have old drivers; you imagined that. I have TAD TD-2002s. Don't worry though. We'll do as you say, not as you do.
              Francis

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              • #52
                But on the subject of those old drivers. The Altec 288 regularly makes it high on lists of the best sounding drivers ever made. The 802, not so much, so I got the TADs.
                Francis

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                • #53
                  I have built one. Corona.

                  I posted it in the Project Gallery.
                  http://techtalk.parts-express.com/fo...re#post1454529

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