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Window secondary glazing question
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July 4, 2023 - 5:04 am
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Hi, wanting to maximise sound absorption at the windows of my home.

First some background context, secondary glazing refers to two separate window frames, providing a primary glazing at the outer face of the wall and a secondary glazing at the inner face of the wall, creating an enclosed space between the two panes. This compares with double glazing, which is usually a single frame with two panes of glass in it, sold as an integrated glazing unit (IGU). The panes of the IGU may be separated by argon gas, but they will be usually less than a 10mm apart. Secondary glazings are said to be better for low frequency sound due to the depth of the enclosed air, at least 100mm of enclosed space between the two panes of glass is recommended to have effect on low frequency sound. (Of course, the wavelength of 100Hz sound is 3432mm, so I question how much effect 100mm of enclosed space can have anyway). It is also noted that having slightly different thicknesses of glass on the primary and secondary glazings may help with sound absorption as the resonant frequencies will be different.

Now, my question, perhaps a silly question. Suppose primary and secondary glazings as described. Would it be better to use the thickest possible glass on the primary glazing (even an IGU), or would it be better to use thinner glass if it ensures a greater than 100mm enclosed space? To put it another way would two piece of thick glass with less than 100mm enclosed space be inferior to two slightly thinner pieces of glass with greater than 100mm enclosed space?

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July 4, 2023 - 1:45 pm
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Windows must be the same density as the wall they are placed within. Their construction methodology depends on the wall desity and the noise frequency and amplitudes.

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July 4, 2023 - 5:47 pm
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Thanks for the reply. I’m trying to block sound coming in rather than sound going out (perhaps I shouldn’t have used the word “absorption ” in my first sentence). My walls are brick veneer. so there should be glass with greater density, but are you saying the density is more important than the thickness of the glass?

I don’t understand what you mean by “must”. I’m trying to block as much sound as possible.

Getting back to my original question. Do you know you know much about the properties of enclosed air chambers (as between two panes of glass). What is the effectiveness of the size of the gap between panes versus the thickness of the panes? I tried looking in Google Scholar for some maths on this but my initial search proved unfruitful. Am I correct in assuming a lot of studies into sound barriers are proprietary, and not in the public domain, or am I just not looking hard enough?

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July 5, 2023 - 7:57 am
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You are placing the cart before the horse. First, you must measure the frequency and amplitude of all noise issues both outside and inside. The barrier you build is frequency and amplitude dependent on noise and the materials you use are selected based on the same frequency and amplitude.

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