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Metamaterial Absorption Technology

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  • mcargill
    replied
    I have built one. Corona.

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

    Leave a comment:


  • a4eaudio
    commented on 's reply
    Now you are just going too far! If I order a Coke and they say "is Pepsi okay", I usually just get a water.

  • fpitas
    replied
    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.

    Leave a comment:


  • fpitas
    replied
    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.

    Leave a comment:


  • tvrgeek
    replied
    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.

    Leave a comment:


  • fpitas
    replied
    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.

    Leave a comment:


  • tvrgeek
    replied
    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.

    Leave a comment:


  • djg
    commented on 's reply
    With that shape they'll just roll and be fine, I really do believe.

  • Liberator of Magic Smoke
    replied
    "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...

    Leave a comment:


  • mcargill
    replied
    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.

    Leave a comment:


  • fpitas
    replied
    djg, paper mache won't be sturdy enough. People will only buy these for PA use. Roadies will be tossing them off a truck. There's no way someone would put this in their living room.

    Leave a comment:


  • mcargill
    commented on 's reply
    A wisp of melancholy hope still slips my grasp
    The summer dusk slides the day into the morrow
    Between then and now, and now, and now
    Translucent and fragile, like wasp paper

  • billfitzmaurice
    replied
    Originally posted by mcargill View Post
    There is probably also a solution using sound diffusion--chaotic reflection instead of absorption--just as diffusion can be used to control room reflections.
    I've seen B&W utilize that technique.

    Leave a comment:


  • djg
    commented on 's reply
    My best friend and I made a papier mache Box Turtle in 4th grade. We layed up the shell on a balloon.

  • mcargill
    replied
    DJG, those of us who take fabrication seriously know that you must want one desperately and immediately, without delay. Designs without one are now pretty much obsolete. The decisive issue is the "Gee!" forces involved in accelerating technology.

    We talk about how important a driver is; we also must pay attention to the whole drivetrain behind it, from the motor and the bass manifold all the way back to the exhaust port in the rear, including the resonator and muffler. The transmission line between the motor and the axial response unquestionably needs a turbo encabulator, though one might limp on without the turbo (with a gain in efficiency offsetting the loss in punch). We therefore all need a supply of meta-materials and trans-substances on hand when fabricating, with unobtanium being the only such that always produces measurable benefits.

    Leave a comment:

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