Best Insulation Density for Sound Absorbtion

Discussion in 'Audio Hardware' started by MC Rag, Apr 13, 2015.

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  1. MC Rag

    MC Rag Forum Resident Thread Starter

    I'm renovating my new home and will be putting in under-floor insulation (suspended wooden floor on wooden joists) and a new rear partition wall (about 100mm insulation sandwiched between acoustic plasterboard) in my music room. I want to sound deaden/insulate as best as possible and have choices of different densities of rock wool slabs http://www.knaufinsulation.co.uk/en...rmerly-known-as-universal-slab)#axzz3XBddu5QY

    So what density slabs do you think would be best - 33 , 45 , 60 , 100 , 140 kg/m3 ? I'm leaning towards 60 at the moment which I'm sure my builders will thank me for.
     
  2. MC Rag

    MC Rag Forum Resident Thread Starter

    OK just doing some reading and found these conclusions to a study:

    • sound absorption coefficient increased with a decrease in fiber diameter, micro denier fibers (less than 1
    dpf) provide a dramatic increase in acoustical performance
    • one of the most important qualities that influence the sound absorbing characteristics of a fibrous material
    is the specific flow resistance per unit thickness of the material. In general, It can be inferred that, higher
    airflow resistance always gives better sound absorption values but for airflow resistance higher than 1000
    the sound absorption have less values because difficulty of movements sound wave through the materials
    • tortuosity mainly affects the location of the quarter-wavelength peaks, whereas porosity and flow resistively
    affect the height and width of the peaks. It has also been said by the value of tortuosity determines the
    high frequency behavior of sound absorbing porous materials.
    • fiber surface area and fiber size have strong influence on sound absorption properties. higher surface area
    and lower fiber size increases sound absorption.
    less dense and more open structure absorbs sound of low frequencies (500Hz), denser structure performs
    better for frequencies above than 2000 Hz.

    • the creation air gap increases sound absorption coefficient values in mid and higher frequencies. At the
    same time, creation of airgap will have minima at various frequencies for various airgap distances.
    • films such as PVC attachment increase sound absorption at low and mid frequencies at the expense of
    higher frequencies

    From this it looks as though the less dense insulation would be better at cutting out the lower frequencies which is probably what I'm looking for so maybe 45kg/m3 rather than 60kg/m3? What do people think?
     
  3. jupiterboy

    jupiterboy Forum Residue

    Location:
    Buffalo, NY
    I think it is going to be frequeny dependent. People always recommend the pink fluffy stuff and great thicknesses of it to deal with low bass. Tuned traps have PVC films that, with air gap, can target specific frequencies.

    Look at some of the measurements from the manufacturers, and you will start to get an idea.
     
  4. Scott Wheeler

    Scott Wheeler Forum Resident

    Location:
    ---------------
    What are you trying to achieve with this? Isolation form the outside? If so just put as much of the most dense insulation as you can.
     
  5. MC Rag

    MC Rag Forum Resident Thread Starter

    Trying to stop sound disturbing my children upstairs when they're sleeping. Music Room on ground floor so will be putting insulation between G/F ceiling & first floor floor. And the partition wall will back onto the stairs so want to stop sound travelling up that way. I think 100mm of 60kg/m3 is the way to go.
     
  6. Scott Wheeler

    Scott Wheeler Forum Resident

    Location:
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    Best way to do that is to put alternating layers of drywall and empty space between the ceiling and floor. Insulation won't matter as much. If you can get three or four gaps you are sound proof.
     
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  7. CoolJazz

    CoolJazz Forum Resident

    Location:
    Eastern Tennessee
    And a great way to do layers of drywall is to stand one off above the other with furring channel. For the cost of a few strips of C shaped aluminum and a second layer of economical drywall, you greatly enhance isolation. As seen here....

    http://www.soundproofingcompany.com/soundproofing101/furring-channel-with-resilient-sound-clips/

    Note the piece pictured that has very open sides, almost looks like a screen. Screw each side to the first layer of sheetrock, then attach the second layer with screws only to the center of the channel. That alone will economically create a lot of help with sound isolation.

    CJ
     
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  8. Tyler Eaves

    Tyler Eaves Forum Resident

    Location:
    Greenville, NC
    I would imagine that isolating the speakers/stands from the floor is at least as important, especially for bass. You don't have to worry about absorbing energy that isn't transferred in the first place.
     
  9. head_unit

    head_unit Senior Member

    Location:
    Los Angeles CA USA
    Yeah, the best way to stop sound transmission is to have the inner and outer walls not touching, using offset studs. That also allows you to thread a continuous blanket of insulation through the whole thing. I dunno the the material you reference is best; mass loaded vinyl is what comes to mind at least for lows.
     
  10. head_unit

    head_unit Senior Member

    Location:
    Los Angeles CA USA
    By the way insulation really doesn't affect the bass. Mass affects bass the most, but very hard to stop all the bass. For c theater applications sometimes bass shakers can be used on those occasions instead of a sub woofer - can work great if dialed in properly
     
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