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Thread: Quick question. Outside wall, more mass is better... or not?

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    Quick question. Outside wall, more mass is better... or not?

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    Hi

    This is one really old debate to me, with an old friend. It's about a garage door and the question is about sound going out.

    Which is the better choice: a) one REALLY thick layer (50 cm) of particleboard, or b) at least two layers, separated by an air gap or gaps?

    I would even tend to think the isolation wall could be made to be thinner in total for the same reduction by using the air gap variant (not to mention the wall in question is the only way to get air in/out so you need to drill).

    But I really simply don't know. Which one blocks the most dB?

    EDIT: I guess I typed the "quick" question too quickly. What I'm referring to here is a LARGE door, so in effect it's an isolation WALL anyway. The basic question is still this. Which one: a) ONE thick, REALLY thick, isolation layer or b) two or more thinner layers.
    Last edited by spitzer; 09-07-2019 at 13:18.

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    Most pro studio doors are high-density, solid core doors...no air gaps.
    There's some use for an air gap...like when building a double wall...but usually those wall already have quite a bit of mass to them.

    One thing to think about...sound is easily transmitted through air.

    At any rate, for a garage door, to keep sound from going out...I think you will need more than what you expect, assuming you're talking about 100% sound containment, though that may not be really necessary, just substantial reduction.

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    I couldnt get an appropriate door so I just purchased a standard hollow core internal door and stuck a sheet of 50mm reconstituted foam completely over the inside of it and so it fitted tightly around the door opening.

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    And my edit to the OP here, since based on the answers there's much room for misinterpretation: EDIT: I guess I typed the "quick" question too quickly. What I'm referring to here is a LARGE door, so in effect it's an isolation WALL anyway. The basic question is still this. Which one: a) ONE thick, REALLY thick, isolation layer or b) two or more thinner layers.

    It would be a door several meters both wide and tall, so not really a "standard" door in any sense. Sorry. Now back to to the matter at hand.

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    Simplified even more: You're building an isolation wall, designed to block sound. There are two approaches. The first one is: you take 10 boards (low density fiberboard) and screw them together to make one massive wall, 50 cm thick. The second one is: you take 4 boards (low density fiberboard), screw 2 of them together, leave a gap (rockwool, whatever, you decide) inbetween and screw the other 2 boards together to make a wall that is a total of 50 cm in depth.

    Both types of wall would have two (four) relatively small holes placed for ventilation.

    Which wall blocks sound more effectively, and how significant is the difference? 5 dB SPL? 30 dB SPL?

    Sorry again and I hope this time I was able to better convey what I meant to convey.
    Last edited by spitzer; 09-07-2019 at 15:17.

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    There are some good BBC papers on this very subject mainly written by G.D. Plumb (G.D. Plumb - BBC R&D). It has been a few years since I last read them but I'm fairly sure that the conclusions were that two walls separated by an air gap were more effective than one wall. The main problem with a single wall is that vibrations are easily transmitted from one face to the other whereas, with a double wall, there is a compliant layer of air between the two structures which eliminates this problem. Of course this assumes that the walls are properly constructed with a compliant layer where the wall meets the floor and any other structure.
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    50cm ~ 20" thick. That's a massive amount of particle board! Figuring a single garage door, 6'x8' (just for ease of use), a single 3/4" thick particle board 'door' of this size would weigh 163 lbs. 26 layers of 3/4" particleboard (not quite 50cm) would weigh over 2 tons!
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    particle board? MDF is dense, while chipboard is much less so. I'd include weight when it comes to describing sheet types. A timber frame with sheetrock on both sides acording to some respected books is less effective than two frames with sheet on inside and out, leaving the interiors as a void.

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    Just to complicate it. You can now get a 'cement fibre board'.

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