There are two classifications for noise control by comparing Sound Transmission using either STC (Sound Transmission Class) or OITC (the Outside Inside Transmission Class). STC rating is the result of the measurement of 16 frequencies after passing through a barrier while OITC measures the attenua- tion ability of a barrier but more weighted to the lower frequencies associated with traffic, aircraft and other transportation caused noise. STC numbers are usually higher than OITC, and the differences between them tend to stay reasonably constant. The key to blocking sound transmission through a window is breaking up the sound waves, and manu- facturers employ a variety of technologies to achieve that goal. Standard impact-resistant laminated glass reduces noise because the (PVB) interlayer has a different density from the glass, breaking up the sound. A standard insulated window with one layer of laminat- ed glass would have an STC of around 32 to 35, a sig- nificant improvement from a standard insulated win- dow with an STC of about 29 or less. Adding a storm panel or an additional monolithic pane to the window can push STC ratings to 39 or higher. Sound needs air to move, so the 1/2 inches to 3 inches of dead air space between the primary and secondary window causes the noise to die. Asymmetrical Glazing (panes of glass of different thickness in one multi- pane unit) is a another approach to reduce sound transmission often at a lower cost than laminated glass or storm panels, because as the sound wave travels through the differ- ent types of materials, it's broken into different fre- quencies which has the effect to “dissipate” the noise achieving STC ratings of 30 to 34 without laminate, and with a price premium as little as 3 percent to 20 percent. The technique also can be combined with other technologies to further improve the window's sound abatement. The best performing sound-control windows incorporate a combination of glass thick- ness, multiple units and lamination. Installation Because the goal of Sound Control Windows and Doors is to both block and breakup the path of the sound through the window or door unit, it is especial- ly important to use noise abatement materials to sur- round the window in the cavity (dense foam is the best), and prevent as much vibration transfer between the wall and the window (utilize neoprene sound isolation shimming, for example). It is even desirable to use neoprene, cork (or other similarly performing material) sill shims to rest win- dows on which will significantly contribute to the dampening effects the use of other sound mitigation materials will afford. The key is to isolate the window or door unit in the cavity, sort of “suspend” it, while doing everything possible to fully integrate the window or door into the water management system of the wall. Finally, the frame material of the window or door can be a major influence on the sound transmission properties. Composite, wood or uPVC windows are best because they have less vibration tendencies that metal window products. Window Fitters Guide to Window Installation 139 ©2022 AWDI, LLC Do not reproduce without permission GLAZING UNIT CONFIGURATION Monolithic (1/4”) Laminated (5/8”) Dual Pane IG (1/4”-1/2”-1/4”) Gas-Filled 1” IG Triple Pane (1/4”-1/2”-1/4”-1/2”-1/4”) Suspended Film IG Asymmetrical IG (3/16”-9/16”-1/8”) Standard Wall (5/8” Gypsum 2x4 16”OC) Block Masonry Wall (4”-8” Hollow) RATINGS OITC STC 29 31 36 40 28 35 24 35 31 39 23 30 25 30 - 39 STC 41-51 SAMPLE MANUAL
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