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Author: | Oberon |
In Reply To: | Sound Control Windows (posted by John) |
Subject: | RE: Sound Control Windows |
Posted At: | 2004-10-05 17:04:28 |
Hi John,
Saying an STC with a "range" of 40 to 47 is like saying that the distance from Chicago to New York is between 1000 and 4000 miles west. It may be true, but it is kind of meaningless for any sort of workable calculation.
STC 40 to STC 47 is an extremely wide range. I would assume that the meaning of a range of 40 to 47 depends on various options available...laminated glass, wider air space, etc...in other words different window systems.
STC is an average of the ability of a window to attenuate sound through an entire spectrum. STC does not address sound attenuation at particular frequency ranges...A window might have an excellent STC, but it might actually perform more poorly than a window with a poorer STC, at a particular frequency range. In other words, you might install a window with an STC of 40, yet a window with an STC of 35 might seem to be quieter to you because of that unit's particular frequency response.
The calculations to label a window with a particular STC value are quite complex and for a window system to be rated, it must be tested and the resulting STC is "assigned" to that particular window.
Realistically, in order to achieve an STC of 40, you need laminated glass. In order to achieve a 47, you need laminated glass, and a pretty wide airspace ( at least 1")between the laminated lite and the monolithic lite....which makes for a rather thick IGU. I say realistically, because to achieve those STC levels without laminated glass, you would need an airspace something like 4" deep between the lites.
What sort of sounds are you trying to mute? Traffic noise, aircraft, people, dogs? It does make a difference.
BTW, I have mentioned it before, but assuming an equal volume of airspace in the IGU, there is NO advantage to using triple pane over dual pane for sound attenuation. I know it is common "knowledge" that triple pane is quieter than dual, but it is not necessarily correct common knowledge.
HOWEVER, if you are looking to deaden traffic noise or other low frequency sounds, then there is a slight advantage to using triple pane over dual pane assuming that both windows are using the same thickness of glass.
If the dual pane is using thicker glass than the triple, then the dual pane may outperform the triple at the lower frequencies. Also, using different thicknesses of glass in an IG construction will also help.
No one said this was simple!
And ultimately, the quality of the window construction and especially the installation makes all the difference in the world!
Hope this helped...