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    • CommentAuthorCX23882
    • CommentTimeAug 4th 2017
     
    I have decided to install secondary glazing, primarily for noise reduction, but I am unsure about the optimal arrangement of primary window, secondary glazing and blinds. Various sources have quoted the optimal gap for noise reduction being 150-200mm glass-to-glass, with 100mm usually being acceptable. That's easy to understand and logical - larger gaps are better.

    What I'm not sure about is the actual physics of it. Is it that certain widths allow the sound waves to be reflected back into the cavity between the two panes of glass, and cancel out, or is it simply a matter of producing greater separation between the two panes?

    I have two options for how to install the secondary glazing with vertical blinds:
    1) Mount the vertical blinds in between the primary window and the secondary glazing, with the secondary glazing on the outside edge of the reveal, giving ~170mm glass-to-glass distance. In this arrangement there is another "object" in between in the form of blind vanes (albeit, not something which will resonate at a frequency that matters).

    2) Mount the vertical blinds in front of the secondary glazing, with the secondary glazing set closer to the primary window. This could probably give 100mm clear glass-to-glass distance.

    Functionally either is fine, because the secondary glazing is horizontally sliding, and the primary windows open out.

    I assume that in terms of noise - option 1 is better. Option 2 would look better.

    Other details - the primary window is a basic float 4/20/4mm air-filled DGU. The planned secondary glazing has toughened 6/8/6mm argon-filled DGU with soft-coat low-e. The units in the secondary glazing are on-paper slightly better than my old DGU, which is why I'd prefer to go for a larger gap for noise reduction.

    Eventually the primary DGU will be replaced, probably with a 4mm float/6.4mm laminate unit.
    • CommentAuthortony
    • CommentTimeAug 4th 2017
     
    100mm is good to help with noise, be sure to leave no gaps or cracks within or round the windows or secondary glazing
    • CommentAuthorCX23882
    • CommentTimeAug 4th 2017
     
    Thanks tony. The frame section I am looking at appears to be open, so I was thinking about filling it with either compressed foam strips or expanding foam, and then sealing around both sides where it meets the reveal and sill.

    I assume that casement style secondary glazing would be better than horizontal sliders, but hopefully the sliders will still be beneficial enough. We have a somewhat rowdy family that have moved in a couple of streets away (!!) as well as a yappy dog directly behind us. It would be nice to block out the noise of both.
    •  
      CommentAuthordjh
    • CommentTimeAug 4th 2017
     
    Posted By: CX23882What I'm not sure about is the actual physics of it. Is it that certain widths allow the sound waves to be reflected back into the cavity between the two panes of glass, and cancel out, or is it simply a matter of producing greater separation between the two panes?

    I haven't looked the answer up but a third possibility strikes me, which is that with narrower spacings there might be resonance effects at audible frequencies. A larger spacing would presumably shift these frequencies below the audible range.

    A blind between the primary and secondary glazing would likely damp any transmission rather than add to it. Why vertical blinds? They require a lot of space to open.
    • CommentAuthorCX23882
    • CommentTimeAug 4th 2017
     
    The vertical blinds are already in place. These particular windows only have openings at one end, and so the blinds draw to one side, stacking over a fixed pane. Plus they were a cat-resistant option :)

    Fortunately the vanes are just 89mm wide, rather than the larger 127mm, so with the depth of the handles there is JUST enough space for blinds and secondary glazing.

    I think I'll stick with the original plan of blinds between the two windows.
    •  
      CommentAuthordjh
    • CommentTimeAug 4th 2017
     
    Sounds like a good plan to me.
  1.  
    Posted By: CX23882

    What I'm not sure about is the actual physics of it. Is it that certain widths allow the sound waves to be reflected back into the cavity between the two panes of glass, and cancel out, or is it simply a matter of producing greater separation between the two panes?



    The attached link to an old Pilkington tech bulletin should answer your questions. Unfortunately the file size is to large to attach to the post.

    https://www.google.ie/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&ved=0ahUKEwjsgo_srMXVAhVSaFAKHYUADGUQFghIMAU&url=http%3A%2F%2Fwww.climatec-windows.co.uk%2Fpdf%2Fspecifiers%2FPilkington%2520New%2520Noise%2520Levels%25202007.pdf&usg=AFQjCNHIrufxdsAcee2CQ0lE85mg2gaaXA
    •  
      CommentAuthordjh
    • CommentTimeAug 7th 2017
     
    Here's the actual URL

    http://www.climatec-windows.co.uk/pdf/specifiers/Pilkington%20New%20Noise%20Levels%202007.pdf

    That's a very useful document. It clearly shows the superiority of a wide gap for acoustic purposes, amongst many other things.
    • CommentAuthorowlman
    • CommentTimeAug 8th 2017
     
    Thanks Dave, and Monty. I've been thinking of much the same in a bedroom facing a road.
    • CommentAuthordelprado
    • CommentTimeAug 8th 2017
     
    Thanks for all thoughts in this thread which is something I am considering as I write.

    It seems that, basically, differing glass thickness is important but having really thick glass or investing in very expensive membranes does not warrant much benefit - and effort should be focused on secondary glazing instead...
    • CommentAuthortony
    • CommentTimeAug 8th 2017
     
    My 3g windows with four layers of gasgates keep noise out fantastically well.

    Heavier the glass the better and different thickness help mitigate different frequencies of sound.

    The 100mm space for sound deadening has to with the wave length of sound,

    We used to line the 100mm space with slotted white painted softboard which helped absorb and not reflect sound waves in that void.
    • CommentAuthorCX23882
    • CommentTimeAug 9th 2017
     
    Thank you for all the responses. The Pilkington document made very interesting reading, and backed up what I thought was the case. Whilst I expected throwing more mass or a wider gap at the problem is the solution, it's good to have some numbers of the relative performance, particularly when it comes to finding a compromise due to cost or space constraints.

    It looks like additional thickness or wider gap has more of an effect than laminating the pane, at least for the frequency range that matters most.
    • CommentAuthorowlman
    • CommentTimeAug 9th 2017
     
    Glass thickness, i.e. extra, will most likely have a knock on effect on the secondary glazing profiles, both in terms of availability, cost, and strength to take the extra weight. This may mean purpose made profiles which again most likely will impact cost.
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