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B Do liquids absorb sound better than solids?

  1. Aug 2, 2016 #1
    I'm brainstorming ideas on how I could possibly create a sound proof box to block out the noise from my servo. I was thinking to create a plastic box with hollow walls that could be filled with some sort of liquid, not water, but maybe something with low viscosity to absorb the sound.

    Would this work better than just having solid walls?
     
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  3. Aug 2, 2016 #2

    jfizzix

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    Something that doesn't transmit vibrations well won't transmit sound well either.

    It might be easier to just stuff the hollow walls with some spongy foam like actually cut up sponges or memory foam, depending on your budget. I'm no acoustic engineer, though.
     
  4. Aug 2, 2016 #3
    I've read that foam materials or very hard surfaces could block sound. I'm having a hard time however figuring out a way to determine which material would work best between the two.
     
  5. Aug 2, 2016 #4

    davenn

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    a wonderful opportunity for you to do some experimenting :wink:

    a vacuum is the best followed by low density materials .... Styrofoam, foam rubber etc
     
  6. Aug 2, 2016 #5

    jfizzix

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    If your servo is not attached to the box, I would have whatever the servo is attached to rest on a bed of foam inside the box, and make the box heavy and hard (aluminum a half inch thick would probably do it or wood a full inch thick).

    If the servo is attached to the box, then vibrations in the servo will be transmitted into the box whether or not the interior is full of foam.

    If it has to be attached, you could glue it to a piece of sturdy foam, and glue the foam to the box.

    These are just idle suggestions, though.
     
  7. Aug 2, 2016 #6
    The servo basically rotates a robotic head. I'm curious if a fan could distort the vibrations created in the air by the servo.
     
  8. Aug 2, 2016 #7
    The foam panels used for thermal insulation in buildings are very good sound insulators as well.
    Air is better than liquids and the foams contain lots of air.
     
  9. Aug 2, 2016 #8

    OmCheeto

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    I think styrofoam can be skipped:

    Question; "Are STYROFOAM™ Brand Extruded Polystyrene Foam Insulation products suitable for acoustical control or sound absorption purposes?"

    Dow; "STYROFOAM™ Brand Extruded Polystyrene Foam Insulation does not perform well either at absorbing sound or at blocking sound transmission as compared to a variety of materials that have been designed and/or are sold for acoustical control/sound absorption purposes. STYROFOAM™ Brand Extruded Polystyrene Foam Insulation is an ineffective sound-deadening material."

    [ref: Dow]
     
  10. Aug 2, 2016 #9

    davenn

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    dunno who Dow is ?

    I have seen it used for sound baffles ... maybe it's not the best, rather just a practical cheaper option
    It's performance for temperature control, I suspect, is much better :wink:


    Dave
     
  11. Aug 11, 2016 #10
    To reduce sound, you need a material that will attenuate the acoustic transmittance. It has to be a compliant material that will absorb sound energy. Higher density materials will transmit the sound better (i.e. the sound waves travel faster in denser objects). A material such as dynamat, which is designed to absorb energy in automobile applications, would probably work for your application. Additionally, even a glass fiber may work as well.

    Also, the frequency content of the sound created by the servo matters as well. Using varying layers of different material make it difficult for all frequencies to pass through. Low-frequencies may need to be filtered out by 1 material where as high frequency may need another.
     
  12. Aug 12, 2016 #11

    sophiecentaur

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    People seem to be ignoring just how good Concrete is at soundproofing. A really good mid-match at an interface between a low density medium (air for instance) and a high density medium (concrete) will reflect vibrations and not let them past. Any good anechoic chamber is built inside inside very thick walls. Of course, loss is another noise reducing factor but both ideas have their place. High mass may be difficult to include in planes and cars but, in a fixed location, mass could be effective as an option. Taking resonances below the frequencies that need screening is also a useful approach. Car door panels are loaded with heavy, gungy sheets which resonate below engine / transmission frequencies with heavy damping. Light doors clunk like expensive heavy doors when damped right.
     
  13. Aug 12, 2016 #12
    The frequencies I need removed are really just the higher pitched ones. All these ideas sound great. What are the sheets put in car doors made of? I'm guessing a sort of acoustic foam?

    I definitely need to run some tests.
     
  14. Aug 14, 2016 #13

    sophiecentaur

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    Car doors are loaded with a heavy bitumen soaked felt. A foam (open cell) foam will absorb mid and high range sounds in air. It doesn't work well at damping vibrations in solids. It's a matter of Acoustic Impedance.
     
  15. Aug 14, 2016 #14

    Nidum

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    Box and box materials need to have mass/spring/damping properties such that they are very unresponsive to vibrations at your problem frequencies .

    Instrumentation boxes used near very high noise sources such as engines on test are lined or covered with a sandwich material of thin sheets of lead and sponge . The same construction is used in protection suits for people working in high noise environments .

    Really though you are solving the wrong problem . Better to reduce the noise from the servo drive . Show us the details of what your assembly looks like ?
     
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