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SOUND SUCKER, "ACOUSTIC ILLUSION"
(c)1997 William Beaty

The device below is a good sound absorber. It probably absorbs certain frequencies much better than others. At first glance you'd think this would be boring. However, the psychological effects are VERY INTERESTING. When you hold the thing up near one ear, you feel as if:

  • the air pressure is falling
  • invisible pillows are drifting around your head
  • your ears are about to pop
  • you are going deaf
  • your head is changing size
  • the size of the room is shrinking
  • you are about to faint

    The effects AREN'T really huge, but they are significant. They seem to vary from time to time, so if nothing happens, try again in some other location. Also note that if you play around with this thing for awhile, the effects don't go instantly stop after you put it down. Perhaps it convinces your brain that your ears have changed shape?

    INSTRUCTIONS:

    Buy a couple large boxes of Dixie(tm) coffee stirrers (a few thousand total.) These look like short, hollow, plastic soda straws, except that they are less than 1/8" in diameter. (Don't use the kind that look flat, they must be round and hollow.) Obtain a straight-sided container, such as a peanut butter jar or a tall, very wide coffee mug. I think the straws need to seal flat against a flat surface. I used a cardboard box with a square of cardboard placed in the bottom. Place the stirrers in the box or jar. Shake them around and pack more in until you have a solid cylinder-shaped array of straws, looking like an insect eye.

    Go into a room which has significant broad-band environmental noise. Close your eyes and bring the open end of the straws-matrix up near one ear. Move it away. Wave it around your head. WEEEEEIRD! Part of the background sounds in the room are sucked up by the device, and it feels as if your ears are filling up with invisible cotton. You really gotta try this. Sometimes nothing happens, but when it works right, the effect is very creepy.

    JOKE:

    Build two of these. Sneak up behind someone and carefully hold the open mouths of the jars near their ears. The victim should exhibit a strong response! NOTE: I FINALLY TRIED THIS AND IT DOESN'T WORK. IT SEEMS TO ONLY WORK IF ONE EAR IS USED. WHEN YOU PUT IT ON BOTH EARS, YOU FEEL NOTHING ODD. Perhaps your brain ignores bilaterally symmetric illusions in "audio space?"

    OTHER THINGS TO TRY:

    I haven't tried duplicating the effect with normal-sized drinking straws. It might work, though the effect is probably stronger (and higher in frequency) with the shorter, smaller diameter straws. Also, you need to use a fairly large diameter container, like 5" diameter or more.

    IDEA: Try building a sort of rotating "Radiometer" with several "paddles", with one surface of each paddle covered with a drinking-straw array. One side of each paddle will act as a reflector, while the other behaves as a good absorber at resonance. Place a needle-bearing in the center of the assembly so the paddles can rotate horizontally. Now play a very loud sound in the room, with the frequency at the resonant absorption band of the drinking straws, and perhaps the "pinwheel" will begin to turn because of radiation pressure differences.

    Try binding the straws together with tape or rubber bands and remove the jar. The effect becomes much less. Obviously a lot of sound is passing through the straws even though the ends of the array constitute a jump in acoustic impedance. The ends of the straws must require plugging before the "black hole" acoustic illusion effect occurs, so that no sound comes from the other side of the array, and so that reflected sound is given two chances to experience friction with the straw surfaces.

    I wonder what it would be like to be near an entire wall of straws? Obtain a 2ft cardboard box, many thousands of coffee stirrers, then fill the bottom of the box with on-end stirrers. Maybe trim down the edges of the box to match the length of the straws. If the "black hole" effect seems less, it might help to include a wood or plexiglass plate in the bottom of the box behind the straws. This will provide a solid acoustic reflector (the cardboard might be too leaky for sound.)

    THEORY:

    This phenomenon possibly involves the "energy sucking antenna" effect. A small resonator, if the Q is fairly high, will build up a strong wave which can act as "anti-sound" and deliver energy into the resonator. Once resonance has built up in the straws, they will efficiently absorb energy in a region 1/4 wavelength in all directions. They should behave like a large "pillow" which absorbs sound and converts it into frictional heat along the walls of the straws. This will only occur at the fundamental and at the harmonics. The box of straws acts as a "comb filter", and in theory it punches a series of slots in the spectrum of broadband noise.

    WHAT THE HELL?

    After playing with this device for many minutes, for me the "floating pillows around your head" effect did not stop! I put the device away and went into another room, and for about half an hour I kept noticing changes in my hearing, as if someone behind me was still waving the stupid device around my ears. I've heard that human ears are supposed to generate sound. Perhaps they employ a feedback system, and perhaps this plastic narrow-band absorber confuses the brain subsystem which performs my sound localization. Or perhaps my brain simply accomodated to the presence of the device (as when the physical shape of our ears is accidentally altered.) Then, when the device was removed, my acoustic perceptions did not return instantly to normal. The acoustic equivalent of "phantom limb effect?"

    Or did I just give myself even *more* brain damage? ;)


    ----------------------------------------------------------------------
    NEW ADDITIONS:
    
    
    Shaping Sound, article at SciAm (perhaps this soda-straw device has
    some of the characteristics of these "photonic crystal" rod-array
    sculptures?  
    
    Also see: Acoustic Sculpture, and
    Sound Science Imitates Art, in Phys. Rev. Letters
    Sonic Architecture, acoustic sculptures
    
    Date: Sun, 15 Nov 1998 13:05:04 +0200
    From: Hamdi Ucar
    To: vortex-L
    
    News comes from PHYSICS NEWS UPDATE.
    
    
    "Taking inspiration from such photonic crystals, and from a beautiful
    outdoor sculpture in Madrid, Francisco Meseguer of the Institute of
    Material Science in Madrid (fmese@fis.upv.es) has designed a metallic
    structure that produces bandgaps in the audible frequency range for sound
    waves entering the material from all directions.  Described at the recent
    Acoustical Society of America meeting in Norfolk, this "sound sculpture" 
    consists of one-meter-long metal bars arranged in a hybrid
    honeycomb-triangular pattern.(See www.acoustics.org/meseg2.htm;  also see
    Sanchez-Perez et al., Physical Review Letters, 15 June;  Physical Review
    Focus, 15 June)" 
    
    See the sculpture at 
    www.acoustics.org/meseg2.htm
    
    John Ernst Worrel Keely, crackpot/fraud, or unsung Wizard of Acoustic Resonance?
    
    Straws chair
    
    Energy Sucking Antennas
    
     

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    Created and maintained by Bill Beaty. Mail me at: .