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New Acoustic Treatment Material/System- Perfect Absorption?

Discussion in 'Studio Lounge' started by DonnyThompson, Sep 20, 2015.

  1. DonnyThompson

    DonnyThompson Distinguished Member

    @Brien Holcombe , @kmetal @Boswell , @pcrecord , @audiokid , ... and anyone else who may be interested:
    "Physicists at Hong Kong University of Science and Technology have experimentally demonstrated a system capable of perfect sound absorption. Acoustic waves go in, nothing comes back out. At all."

    At this point, I'm neither a proponent or a nay-sayer. I don't know enough about it yet to be either; nor do I yet have any suggestions on its practical use in a recording/mixing environment.

    I'm simply posting the article here for those who might be interested in reading it, and creating an environment for relevant discussion.

    I'm just the messenger here. In short, don't shoot me. Okay? Okay. ;)
    Here are some excerpts:

    "In a paper published in the Applied Physics Letters this week, the Hong Kong researchers describe a rather more active absorption system (but not totally active) composed of two resonators, both of which are tuned to the same frequency, which is itself "impedance-matched" to the background medium, e.g. the open air or whatever surrounding the acoustic absorber. The result is sound-killing destructive interference."
    "Working against the material's absorption potential is the resonator's natural coupling to the acoustic radiation of the surrounding medium. The sound waves want to scatter, but now at the frequency of the resonator. The second resonator is ready for this and is tuned to just the right frequency to create destructive interference. The waves that would have scattered are canceled out."
    "The end result of the new and improved version is 99.7 percent total silence, according to the current study. Which is pretty quiet."

    Here's a link to the paper mentioned in the first quote above; which appeared in the industry publication, Applied Physics Letters, where the material's use is discussed:


    "Each resonant cell of the metasurface is deep-subwavelength in all its spatial dimensions, with its thickness less than the peak absorption wavelength by two orders of magnitude. As there can be no transmission, the impedance-matched acoustic wave is hence either completely absorbed at one or multiple frequencies, or converted into other form(s) of energy, such as an electrical current. A high acoustic–electrical energy conversion efficiency of 23% is achieved."

    Personal Observations:

    Based on what I've gathered so far, I will say that I find this to be very intriguing, and quite a discovery.
    Although, I'm not sure if this material/process- or something similar - has been tested previous to this discovery or not; nor do I know whether this most recent discovery is truly new and cutting edge, or if it's just a better-built mousetrap based on past research, or past similar discoveries and/or inventions.

    What I've not seen mentioned (yet) are certain parameters of the tests, one being the SPL/Velocity that this material was tested at.

    Without down-playing the discovery, or the potential importance and practical application of the system, I do feel that the title of the article is misleading, as I found a section within that mentions that the material reaches limitations in its effective absorption coefficient/rating starting at around 250Hz and on down...
    So, if this is true, then it's not really a "complete" absorption system, and low-frequency RT60 attenuation methods would still need to be implemented, if it were to be considered for use in a mixing environment.
    (There's also the very real concern/question as to whether one would want to mix in what would amount to an anechoic environment).

    Anyhoooo... I thought I'd share this.

    So... Thoughts? Comments?



  2. Sean G

    Sean G Well-Known Member

    I click on the link
    and also
    and all I get is a big prancing digital horse...must be some error with the site.
  3. DonnyThompson

    DonnyThompson Distinguished Member

    wow, that's weird... me too. It was working a few hours ago. Although this link still works ( for me): http://www.nature.com/nmat/journal/v13/n9/pdf/nmat3994.pdf
  4. DonnyThompson

    DonnyThompson Distinguished Member

    Okay... let's try this.
    Sean G likes this.
  5. Sean G

    Sean G Well-Known Member

    While we are on the subject of diffusion, I stumbled on a YT video where a guy attached six 12 x 12 inch acoustic tiles on a canvas stretched frame which measured 24 inches x 36 inches (like you buy from an art supplies store) with spray adhesive then mounted the frame on the wall.
    -My question would be, as this allows the actual tiles to sit approximately 2 inches from the wall (the same thickness as the tiles), would this improve the diffusion by mounting the tiles this way?
    It seemed a novel approach and an easy way to mount and remove them, or would the frame create some sort of vibration coming into contact with the wall if it was only mounted with say, a picture mount as opposed to fixing it in a more secure way??
  6. Boswell

    Boswell Moderator Distinguished Member

    It's relatively easy to see how the total absorption could work at a single frequency or narrow band of frequencies, but over a useful audio range? I'm unconvinced.
    pcrecord likes this.
  7. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    " completely absorbed at one OR multiple frequencies..."

    I think maybe they would agree with boz on this. It's an interesting design for narrowband sealed traps. i think of this as almost perfect "nulling" where what you have left is the little bit that didn't cancel out. If you figure the front and back were perfectly identical and tuned, then the variable would be where the sound was striking the device. If you aim (directional) sound right at the front surface, it resonates, it then passes energy to the rear which sympathetically vibrates, but out of phase. Since there is energy loss in the transfer their is a little bit left which is the narrow peak of the trap.? Not sure bout how it all works.

    This is the paper the designers wrote. http://scitation.aip.org/content/aip/journal/apl/107/10/10.1063/1.4930944
  8. Brien Holcombe

    Brien Holcombe Well-Known Member

    Pretty sure they are talking about ear plugs.

    In any event, "masking" frequencies has been around for decades but they may have developed a better mouse trap in this respect that can be tuned to a very specific frequency which we do not have as of yet.

    Did they say when it was coming to a Home Depot near you?

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