Sound Attenuation in Walls - Quietzone

Discussion in 'Archived Threads 2001-2004' started by Doug_B, Feb 22, 2001.

  1. Doug_B

    Doug_B Screenwriter

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    I'm having some construction done on my family room, so I have an opportunity to decrease sound transmission through the walls and ceiling before buying my new HT audio equipment. I found some info on the Owens Corning web site about their Quietzone solutions, specifically acoustical batts that can be placed inside the walls and above the ceiling, just like insulation. Any experiences with this stuff? How expensive is this? My room is 13 x 20 x 8. It will not be a dedicated HT room, but I'm willing to spend some amount of $ on sound attenuation so I can raise the volume a bit at night. The web site suggests about a 20% decrease in sound transmission, but I don't have a feel if this is a significant decrease. Any other options that are not "extravagant" and that a non-HT savvy contractor or I (newbie) can perform?
    Thanks.
    Doug
     
  2. Greg Monfort

    Greg Monfort Supporting Actor

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    Sound attenuation has to be built-in for LF, so requires thick double flex walls, etc.. WRT O-C wall treatments, I was stunned at the prices listed in a HT mag article sometime back. It was something like eight grand for the complete package in an average size room, though I don't know the cost of the particular products you mentioned.
    WRT to 20%, 20% of what, and in what BW? If they mean that the treatment is 20% absorptive, then:
    dB = 10*log[1-(20/100)] = a whole 0.97dB drop, BFD.
    If they're saying it's 80% absorptive, then it's a 6.99dB drop, quite a bit.
    GM
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    Loud is beautiful, if it's clean
     
  3. Doug_B

    Doug_B Screenwriter

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    Greg,
    Thanks for the response. Yes, knowing the units of measurement associated with the 20% figure would be useful. The OC web site states that a single layer of the acoustic batts results in a perceived noise reduction of 20%, which means ???
    Yea, if this cost is anything close to the cost of the treatments you reference from the HT Mag article, the kids are just gonna have to put up with the sound [​IMG]
    Doug
     
  4. Greg Monfort

    Greg Monfort Supporting Actor

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    >The OC web site states that a single layer of the acoustic batts results in a perceived noise reduction of 20%, which means ???
    ====
    Well, a 50% reduction is half power, or -3dB, so 20% is -0.97dB, or barely perceptable if this format is being used.
    Since their website is to some extent for the layman, they may mean it literally, in which case it would be a straight percentage, but here again, you would need to know the BW, as a 20% perceived difference would be frequency dependent due to our very non-linear hearing response. A perceived doubling of loudness (3dB) at 3.5kHz equates to 30dB (10x increase)at 30Hz according to the Robinson-Dadson equal loudness curves of human hearing perception.
    Anyway, 20% doesn't 'sound' like much to me, unless they mean that if the peaks are 105dB, then it's reduced by 20% to 84dB, which I seriously doubt. If it does, then it's worth a ~high price, as this represents a 99.2%! reduction in acoustic energy.
    GM
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    Loud is beautiful, if it's clean
     
  5. Doug_B

    Doug_B Screenwriter

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    Greg,
    The only thing I could find on their web site that may better quantify the impact of the batts is the following statement: "QuietZone acoustic batts can improve
    conventional wood stud walls to a Sound Transmission Class
    (STC) rating of 39." Means nothing to me, but maybe you or someone else is familiar with this rating system?
    Thanks.
    Doug
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  6. Greg Monfort

    Greg Monfort Supporting Actor

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    STC = Sound Transmission Class, or a number to represent the averge SPL absorption of walls/ceilingfloor. It has a BW of 125-4kHz. This is one of the values I was asking for last night, but I had a mental block and couldn't think of what it was called. The other is NRC, Noise Reduction Coefficient, which is expressed as a percentage/frequency. Amazing what some sleep will do for the old gray matter. [​IMG]
    Anyway, STC = 39 means it attenuates whatever the in-room average SPL is -39dB, but doors, windows, openings, will decrease it (worse). It also decreases with frequency, so at 125Hz, it may only be the 20% listed, or -21dB, but at 4kHz be -57dB.
    Below 125Hz, it takes sheer mass to absorb the energy, plus the batts to finish absorbing what's left, so I highly recommend you at least double up on wall thickness, and use solid or well insulated doors, etc.. If no drywall is installed yet, two layers of MDF makes a good wall, otherwise, a second layer of MDF.
    And of course, sound transmission takes the path of least resistance, so doing the walls without matching it on the floor/ceiling, partially defeats your efforts. [​IMG]
    Good luck with it! [​IMG]
    GM
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    Loud is beautiful, if it's clean
     

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