Sound retarding "reduction" for a wall.

Discussion in 'Remodel Forum & Blog' started by Semon, Jun 3, 2013.

  1. Semon

    Semon New Member

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    Tn.
    What is the best way to retard sound between bedroom walls?
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    This is best done when the original wall is installed, but adding a second layer of drywall on each side and sealing around the electrical boxes will help. If you hang that second layer with the noise isolation clips, it gets a bit better. If you want even more, (this gets costly!) they make composite drywall panels that have a layer of lead sandwiched in between layers of drywall. There is also some special rubber caulk that you can use to attach the second layer of drywall. Solid panel doors help verses hollow core, and gaskets around the door along with a retracting, automatic sweep at the bottom can help. If there is a common HVAC duct, sound can travel through that, and that can get harder to fix without tearing a lot out.
  3. Semon

    Semon New Member

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    Tn.
    How about using regular insulation (bats) in interior walls?
  4. hj

    hj Moderator & Master Plumber Staff Member

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    sound

    The studs which are attached to BOTH sides of the wall conduct most of the sound so insulation will not help that. The two wall surfaces have to be isolated from each other, either by separate wall structures, i.e., alternating studs with insulation woven between them,or, isolation clips/rails to isolate the drywall from the studs, or some other method, such as extra drywall to create a "mass" that is less susceptible to transmitting the vibrations.
  5. Dana

    Dana In the trades

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    Adding insulation in the wall DOES in fact reduce the sound transmission, and by quite a bit. Contrary to hj's assertion, most of the sound transfer between rooms is via air, not the framing. Air-sealing around electric boxes with an always-flexible acoustic sealant caulk (Tremco makes one of the better acoustic sealants) or "Windows & doors" low expansion can-foam counts, as does caulking the studwall plates, and wall gypsum where it meets the floor or ceiling with acoustic sealant.

    Then, adding well-fitted batts or blown cellulose/fiberglass cavity fill in a standard 2x4 partition wall provides a reduction of about 35-40 STC points(!). Don't forget to block the ceiling & floor joist paths too, if you have access- when you take the wall's transmission paths down 40 STC points the ceiling or floor joist bays can start to dominate. Recessed lights into open joist bays are an acoustic super-highway, but even empty joist bays and unsealed electrical/plumbing penetrations in the ceilings & floors is more than a mere farm-road path for sound.

    The wallboard layers are effectively a timpanic surfaces (like the soundboard on a piano), and while adding mass to them helps, adding a mass with a vibration-attenuating adhesive like Green Glue (tm) helps.

    If you're re-framing a partition wall there are other schemes to take it down even further, (staggered studs, furring, partial-thickness batts, etc. etc.), but for retrofitting blowing the cavities with low to mid-density cellulose or fiberglass and air sealing is step-1, followed by double-layering the gypsum using flexible adhesives.
    Last edited: Jun 4, 2013
  6. Semon

    Semon New Member

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    Tn.
    Thanks for the info

    Lee
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