Window Choice With Low Sound Transmission

72chevy4x4

I've looked into window choices to reduce sound transmission and found the STC, Sound Transmission Class, is the measure and windows with larger distances between the panes and laminated glass, offer higher ratings (higher the better).

So...I found the Simonton 5500's offer laminated glass, which are 'reasonably' priced as well as a few others including a Pella Architecture (??) series. I'm guessing a 3 pane would be better then the 2 pane, but not sure if it's better than a 2 pane w/ laminated glass.

Anyone of you guys have experience/knowledge in window choices w/ higher STC ratings? Any help would be apprecatied!

Patrick

Harvey offers an acoustical with an STC 40 The higher the rating the more sound it keeps out. Also improves the U value and R value

72chevy4x4

do you have any cost comparison info Patrick? Do I recall your Harvey rep was up north in PA?

Grumpy

Look into "whisper quiet" glass. It is available on various different manufacturers including Simonton.

Amber

Milgard Quiet Line Windows will get you an STC 44 with 3/16 over DS glass.

Oberon

Although I avoid discussing specific window brands, here is a (long) general overview of window sound performance that hopefully might help in your research...

As already noted, 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 – and while the attenuation characteristics of specific products at specific frequencies do exist, they are not generally available to the public. It isn't so much that anyone is trying to hide them, it's more like information overload in most cases.

Sound Transmission Class is a laboratory rating based on some very specific criteria within a very specific frequency range. STC is designed primarily 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 does not say which of those products would perform best at what specific frequencies.

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.

At the basic level there are three primary issues to consider when dealing with unwanted "noise" – the frequency, the level, and the duration of the 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. While we may hear a sound at a relatively low decibel (or sound pressure) level at a specific frequency we may also be unable to hear an even louder sound at a different frequency. That's why frequency response is weighted.

Sound duration is added into the mix because even a relatively quiet sound can become annoying when it is persistant. Using figures derived from these three descriptors, a sound professional can determine what is required to attenuate (opposite of amplify) the inappropriate sounds.

When considering window glass sound performance, there are three primary considerations 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, might 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 while 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 some 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.

And as a general observation, different thickness lites in an IG configuration contributes more to lower frequency noise attenuation than it does to higher frequency attenuation. 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 windowas well - but often 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, if the three lites in a triple pane are the same thickness then there is little, if any, advantage to using triple pane.

Finally, 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 – cool how that works right into the explanation!

A single sheet of 1/4" laminated glass consisting of two 1/8" lites and a PVB interlayer actually has 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 - and the overall STC rating between the two is very close as well.

And finally (again), whichever window you decide to choose, it MUST be installed correctly. I would venture a guess that better than 90% of all window problems involve installation, and if you want to stop sound from penetrating the unit, then installation is vital.

A fixed, versus an operating, window is usually going to give you much better sound attenuation. However, having a house-full of windows that can't be opened is not very appealing to most people, so ensure that any operating window MUST be tight when closed for maximum sound performance.

Grumpy

That was very informative. Do you mind if I print that and share it with my specifiers?

Tru_Blue

You mentioned STC ratings but there is another rating system you may wish to consider as well. The ability of a window to reduce outside noise is commonly rated in 2 ways - either via its Sound Transmission Class (STC) or via the Outdoor-Indoor Transmission Class (OITC). The higher the number the better the window is at reducing sound.

A noise reduction of 10 decibels represents cutting the noise level in half. So a rating of 25 (which is 2-1/2 times greater than 10) means that the product reduces the outside noise by approx 25 decibels, cutting the noise in half 2-1/2 times, or cutting it by over 80%.

STC ratings have long been the standard by which window companies have measured noise reduction. However, they only give an indication of noise reduction of high frequency sounds such as voices, birds, etc. OITC ratings are relatively new, but would be a much better indicator for you of noise reduction because they're based on lower frequency noises such as traffic, lawn mowers, etc. Therefore OITC ratings are usually a few points lower than STC ratings because the lower frequency sounds are more difficult to reduce.

The simplest recommendation would be to get laminated glass in an insulating glass unit. Laminated glass is highly effective in reducing noise thus improving STC and OITC ratings. It's produced by permanently bonding two pieces of glass together with a tough plastic interlayer between them. It also blocks 99.5% of the sun's ultraviolet rays, protecting furniture, etc. from fading. Other noise-reductions variables are mentioned above in Oberon's excellent post. (Oberon, we meet again!)

Double and triple glazed windows (non-laminated) typically have an STC of upper 20s to low 30s, while laminated is around mid to upper 30s. In some cases you can reach 40 but it can be pretty costly. Fixed windows are typically about 1 point higher than vent windows.

Both of the brands you mentioned, Pella and Simonton, offer such a glass system. Many other companies offer laminated glass as well. Good luck & best wishes!

constructionldr

Amazingly enough the pella windows I have installed in the past have actually been known to let in more noise than the originals. I install certainteed alot..and across the board they seem to offer some of the best features for the money...and as far as backing, I had a customer with windows 15 years old and the company still backed there "old" design. Not sure on sound though. Pella just seems to be a "name" anymore

Oberon

Grumpy, thanks and feel free to use whatever you would like.

Hiya Tru_Blue and welcome to Contractor Talk! This is a good board, you will enjoy it.

And I second Tru_Blue's comments on OITC. It is a better indicator of sound performance than STC (my opinion), but it can be harder to find because not everybody uses it.

Tru_Blue

Constructionldr brings up an interesting point. Sound/noise can actually be worse with new windows than they were with the old windows, regardless of material or brand. If one had double glazed windows (say, for example, single glazed with a storm window) and then replaced them with a double glazed insulating glass window, both before and after they have two panes of glass; no change there. However, the new insulating glass window, although presumably a better insulator (assuming they have Low E glass or a gas filling), has the panes only about 1/2" apart, while the old window had one of the glass layers (the storm window) spaced significantly farther away. The farther they are spaced apart the better it is for sound reduction. The STC of single glazed with a storm is about a 30, while insulating glass is about a 28 (this varies with window type, size, how airtight the window is, etc.). Also, the storm window system might have had the two respective layers of glass (the single glazed prime unit and the storm window) with different glass thicknesses, which again is better for sound reduction. Also the old windows might have been painted shut, which interestingly enough is better for sound reduction. The hypothetical new windows would typically have two panes of glass the same thickness, spaced only about 1/2" apart at most, and would actually open, all of which may be worse than the original window if one only considers sound reduction. The gas filling has pretty much no effect on sound reduction. So therefore if one replaces their windows with wood, aluminum, vinyl, or fiberglass windows, and gets double glazed windows without laminated glass, they should not expect a significant reduction in sound but in fact might have an increase in sound. If the old windows are old and very DRAFTY, any new double glazed window that is more airtight should hopefully be an improvement on sound reduction. Again, one can reduce sound transmission by using laminated glass (the best!!), spacing the glass farther apart (such as using a storm window), using two or more different thicknesses of glass, getting fixed windows instead of venting, or using triple glazing with one of the layers being a different thickness (triple glazing with all three lites being the same thickness helps to block out cold but doesn't do much for sound reduction). For all you window-selling pros out there, please consider telling your customers (if the subject comes up) that the new windows will not significantly change sound reduction, unless they employ one of the strategies mentioned above. New windows have many advantages (such as low maintenance, energy-efficiency, easier operation, etc.) but depending on the glass being used, noise reduction may not be one of them.

72chevy4x4

Oberon and Tru Blu, thank you for the in depth comments; your sharing of knowledge is appreciated.

How about a piggy back question-is it possible to create a vacuum between the panes? Surely some sort of spacing (lites) would be necessary to keep them from imploding, depending upon the amount of vacuum. Would a window system be able to maintain a vacuum for a significant length of time? Finally, if achievable, would the lack of air create a considerable increase in the STC (or conversly the OITC)?

Oberon

You are welcome...

Folks often comment how much they like their new dual pane windows for the "sound" improvement versus their older units.

Some folks will comment that they are hearing more sound thru the newer windows than they did thru the older versions - often for the reasons that Tru_Blue noted already.

But, one change that can also affect a homeowners perception of the sound thru the window is that the newer windows have a different frequency response or that the newer windows have actually cut back on the constant "hum" of background noise so that now the homeowners are hearing sounds that (a) were always there, but were being covered up by the background noise or (b) they are hearing different sounds because of the change in frequency of the sounds coming thru the windows. These types of changes can be MUCH harder to quantify and can be really annoying for all concerned.

To answer your question 4x4, current technology does not allow the use of a vacuum between the lites of a dual pane window. It is quite possible to suck the air out of the space and to keep it empty, but the glass would bow inwards and eventually either break or at best, touch at the center of the unit.

If the lites touch all bets are off - you then have a thermal short circuit as well as a sound proagation shot circuit.

In the event that you could create a vacuum between the lites, you theoretically can effectively stop all sound transmission thru that space with only the frame transmitting sound waves.

dougthewndowguy

Milgard Windows has the lowest STC ratings for a standard vinyl window.

You can buy them online at www.1stwindows.com

Good luck.

Dougasl
president
www.1stwindows.com