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There are three words to consider when dealing with sound performance of any material – density, stiffness, and damping. There is also little thing called the Mass Density Equation that applies specifically to sound attenuation:
1. Each time the frequency of a measurement or the mass per unit of a single layer partition is doubled, the transmission loss is increased by 6db.
2. To increase the sound transmission loss of a partition by 12db, at all frequencies, the mass per unit area must be increased by a factor of four.
3. An increase of sound transmission loss to 18db requires that the mass per unit area of the partition be increased by a factor of eight.)…
Windows, doors, walls are all rated as to their ability to deaden or attenuate sound based on something called an STC or Sound Transmission Class. STC is an average of an objects ability to attenuate sound across the entire sound frequency spectrum. STC 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.
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, for example.
By the time we are teenagers we have generally lost the ability to hear above about 13,000hz which as I remember is something mother always warned us about - going deaf - or was it stop or you'll go blind? I always get those confused.
Anyway, traffic noise is generally a low frequency sound, and unfortunately, low frequencies are much harder to attenuate (opposite of amplify) or block than are higher frequencies...consider how often you hear the bass sounds from the neighborhood kid's car stereo and not the higher pitch tunes when he is coming down the street.
When considering windows, for example, there are generally three options available 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, may 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, consider a triple pane with two 1/4" airspaces and a dual pane with a single 1/2" airspace...both using 1/8" glass...the STC will be identical if the IGU's are the same dimensions.
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 the other lite "passed".
And, as always, the quality of the construction and especially the installation cannot be overstated!
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