# Soundproof Windows



## BlueJello (Oct 29, 2007)

Not sure if this is the right category as I couldn't find a topic heading just for windows. 

Has anyone installed soundproof windows and do they really work? I live in a highrise condo where neighbors like to hang out on their balconies. The problem is that I can hear every word. And how much do they run if I'm looking for my small bedroom window? 

Thanks for any advice.


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## oberon (Apr 29, 2006)

Hi BlueJello,


This is going to be a rather long reply, but hopefully it will give you a little background to help your research...


Windows, doors, walls, whatever, are all rated as to their ability to deaden or attenuate sound based on something called STC or Sound Transmission Class. STC is an average of an object’s ability to attenuate sound across a fixed frequency spectrum of approximately 100hz-5000hz. An STC average (what you will be quoted if asking about STC of a specific product) does not provide specific frequency-deadening information which may be what is needed if you want to block a specific type of unwanted noise – for example traffic noise – but, the attenuation characteristics of specific products at specific frequencies do exist, but they are not generally available to the public.. 


Sound Transmission Class is a laboratory rating based on some very specific criteria within a very specific frequency range. STC is designed to test the frequency range where the human voice will be the predominant consideration. 


While using STC to compare the sound-blocking ability of different window styles or brands is certainly not a bad idea since, generally speaking, a window with an STC of 40 should outperform a window with an STC of 35 – STC is sort of like mileage ratings on a new car – not always as useful as one might hope and that 40 versus 35 is for an overall rating – it does not say which of those products would perform best at specific frequencies – again blocking traffic noise for an example. 


STC is a rating that is independent of the conditions under which the window will be used – meaning that it does not take into account the actual field conditions of the assembly. These conditions might include background noise, window area, even the level of sensitivity to noise of the occupants. Noise reduction requirements are affected by these conditions so that windows with the same STC might have very different NR requirements when used in different situations. 


But, at the basic level there are three primary issues to consider when dealing with unwanted "noise" – the frequency, the level, and the duration of said noise. 
Sound frequency and sound level are combined into what is called a "dBA" – or A-filtered decibel value – in order to quantify the sound in relation to the human perception or ability to hear it. In other words, we all “hear” (no pun intended – really!) about the specific dB level at a rock concert or at the airport, but we don’t hear “evenly” across the whole sound spectrum. In other words, we may hear a sound at a relatively low decibel (or sound pressure) level at a specific frequency and yet be unable to hear an even louder sound at a different frequency. That is why frequency response is weighted. 
Sound duration is added into the mix because even a relatively quiet sound can become annoying when it persists for a certain time. Using figures derived from these three descriptors, a sound professional can determine what is required to attenuate (opposite of amplify) the inappropriate sounds. 



As humans we are born with the ability to hear from approximately 20 to 20,000 hertz. Hertz, or Hz, is how sound frequency is measured - like electricity is measured in volts. By the time we are teenagers we have generally lost the ability to hear above about 13,000hz. Since the human voice tends to fall between 500hz and 5000hz, the loss of higher frequency sounds is not usually a big deal. 


When considering window glass performance there are three primary products to take into account for maximum possible sound attenuation. 


First is laminated glass. 

Second is a wider airspace between the lites. 

Third is different thickness lites within the IGU or Insulating Glass Unit. 

Fourth would be a combination of all three. 


Airport windows, as an example, generally have laminated glass on both sides of an IGU in an aluminum frame and with a maximum airspace between the lites. In an airport the primary concern is sound attenuation and energy efficiency is secondary. I mention this because the width of the airspace and the choice of window framing material affects both sound and energy efficiency. 


Some folks will suggest triple pane glass for its sound deadening ability, and while triple pane may be a slight improvement over standard double pane at lower frequencies due to the additional density of the extra lite, overall there is no difference in STC rating between triple and double pane provided that the overall airspace between the panes is constant between the two constructions. 


In other words, a triple pane with two 1/4" airspaces and a dual pane with a 1/2" airspace – both using 1/8" glass – will have the same STC assuming that windows are otherwise the same.


Using one thicker (3/16") and one thinner (1/16") lite in an IG construction may also help deaden sound because each lite is transparent to a different frequency and each lite will then attenuate the frequency that passed thru the other lite. 


As a very general rule, different thickness lites in an IG configuration (for example 1/8” and 3/16”) contributes more to lower frequency noise attenuation than it does to higher frequency attenuation, yet oddly, using different thickness lites does not contribute significantly to overall STC performance as well as the other options – such as using a wider airspace in the IG unit.


Stopping unwanted sound thru any material is determined by three things – mass, stiffness, and damping. Increasing the mass of a window by using thicker glass will increase sound attenuation and the change from a single pane window to dual pane or triple pane IGU to a window will add glazing mass and may improve sound performance thru the window; but not as much as might seem obvious. 


So why do folks with new dual pane windows, after living with single pane, often comment that the improvement in blocking unwanted outside noise? Often, this is due to the replacement window being tighter than the previous older window, but also the addition of the airspace between the lites of a dual pane – rather than to the effect of the additional lite, unless as mentioned the lites are different thicknesses – can have an effect on sound propagation. So in that sense, the additional lite in a dual pane window improves performance over a single pane by the formation of the airspace. 

But this doesn’t always apply when adding triple pane due to the decrease in the airspace between the lites overriding the potential advantage of the additional lite.


And, since increasing the stiffness of glass isn't really practical, what about damping? 


Inherently, glass has very little damping ability, but when putting a layer of a more viscous material between two of lites of glass we substantially increase the unit’s ability to dampen sound – thus the advantage of laminated glass which just so happens to be a product that has a layer of more viscous material between two lites of glass.


A single pane of 1/4" laminated glass consisting of two 1/8" lites with the plastic interlayer actually has just about as much sound blocking ability as a 1/2" lite of monolithic glass. The monolithic glass tends to do better at mid to higher frequencies while at the lower frequencies the performance of ¼” laminated and ½” monolithic tend to be about the same as well as the overall STC rating.

When you mention soundproof windows are you speaking generically or specifically about the company with the same name?


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## BlueJello (Oct 29, 2007)

Wow, thanks. I was talking about just soundproof windows in general. I didn't know there is a company with that name. All I want is a good night's sleep without having to hear my neighbor's conversations. I'll check for some vendors in my area. Thanks again!


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## oberon (Apr 29, 2006)

you're welcome. 

and good luck in your search!


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