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quick sound insulation question

Discussion in 'Home Cinema Building DIY' started by bockster, Apr 30, 2005.

  1. bockster

    bockster
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    sorry if this is a stupid question, but, when people talk about 'insulation slabs', do they mean the rockwool/fibreglass type, which i suspect, or the polystyrene slabs also available.

    do both these materials act as good sound insulation? if so is one better than the other?

    my task is not really hc, but only to sound insulate between two bedrooms. i will remove the plasterboard from one side of the stud wall, fit the recomended slabs, and then refit two layers of normal plasterboard.

    i've seen recomended that you should use one layer of 12mm, and one layer of 9mm! is this because the different thicknesses stop different frequencies?

    thanks in advance

    bockster
     
  2. Gary Lightfoot

    Gary Lightfoot
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    Hi Bockster,

    Yes, the slabs are like those you can get from B&Q or Wickes. They do a high density 30mm slab which is supposed to reduce more sound transmission than the non HD slabs.

    For soundproofing to work well, you need mass and isolation - the two layers of plasterboard are the mass - use two layers, but one 1/2inch and one 5/8inch will be betetr than using one 9mm with teh 12mm. Glue and screw them together using no-more-nails or similar. I've seen someone mention using three layers of 9mm as well. I believe the reason for this is because each thickness will have its own resonant frequency, so using different sizes should help to reduce it.

    kisolation is achieved by building a new 4x2 stud wall an inch in front of the existing wall - the 1inch ar gap is the isolation needed to reduce the transfer of sound from one room to the other.

    fitting rockwool into the existing wall will help to reduce the transfer of some frequencies and in-wall resonance, but without an air gap the reduction will not be as good as it could be. it will be an improvement on what you have though. Another layer of plasterboard in the other room may help a little too.

    To further reduce sound transmission, you should use silicon or similar to seal all edges around the floor, walls and ceiling. Also make sure the door seals well including at the bottom if that's on the same wall that you're trying to soundproof.

    Gary.
     
  3. bockster

    bockster
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    cheers gary

    i,m starting to wounder though, how far to go, because obviously the sound will travel quite easily through the doors and across the landing! i need to make the wall better but not fantastic! i'm thinking now, will the hd slabs be enough without the extra layer of plasterboard!

    part of the reason for cutting this corner is if i make the wall thicker then i have to mitre 1/2 inch off each of the coving, dado and skirting to make good. i only want to mess about on one wall if possible, not least because i recently decorated in there before realising how much noise transmitted!!

    i wounder if there are any more possibilities without making the wall thicker?
     
  4. Gary Lightfoot

    Gary Lightfoot
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    I don't think there are any other ways other than turning the volume down.

    You've nothing to lose by installing the slabs in the existing wall, so at least try that. If you make the wall thicker just by adding another layer of plasterboard, you don't have to remove the existing dado etc from the adjacent wall and miter it, add the plasterboard and refit the dado/skirting and trim a little off the end - the stuff you refit can be cut to the correct shape and any gaps filler with filler or no more nails etc then painted. That removes the need for removing the stuff from the other wall and making a mitre. You'll be surprised how many houses have had that done somewhere or other, but you don't know it was done that way until you remove it.

    The door frame may look a little odd so you may have to get some new wood for the inside of the door frame as it will now be 1/2" wider.

    Gary.



    Making the door air tight will make a lot of difference - even a keyhole slot can let out over 10dbs of sound, so you have to make sure there are no air leaks out of that room to the landing. A denser, solid door will help too.
     
  5. bockster

    bockster
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    o.k.
    some time has passed, and i still have'nt got round to doing the work yet! but getting closer. i went up the loft and discovered that the existinjg wall is not a studwork timber wall as such. it appears to be 2 layers of plasterboard preassembled back to back and joined with vertical columns of honeycomb cardboard about 4" wide then 10"gap, then 4"cardboard, then 10"gap, etc, etc! still with me? therefore i think it best not to tear off one side!

    so, my plan now, is to simply screw battens onto existing pb, just deep enough to accept the 30mm hd slabs, and then a single layer of 12.5mm pb. this will just fit perfectly without encroaching on door frame. however my question is, does plastic sheeting have any soundproofing qualities when built into a wall, just behind the pb? should be no condensation issues as both sides of wall are internal? and any benefits would be for almost zero thickness! plus its cheap!! anyone ever considered/tried/have knowledge? please let me know

    bockster
     
  6. mattym

    mattym
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    no benifit from plastic sheet that i know of, the only thin materials that will affect sound transmission are the heavy rubber sheets you can use or GreenGlue, but GreenGlue isnt in the UK yet...have you looked into acoustic plasterboard? slightly denser than your average PB
     

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