May 29th, 2014
Stay Tuned for Sound Control
We spend a great deal of time talking about and comparing the energy efficiency of windows. But now that summer is upon us, it is time to focus another great reason to replace those old windows: peace and quiet!
The sounds of lawnmowers, screaming kids, barking dogs, motorcycles, trucks, planes, trains and automobiles can all be dampened by new windows.
The STC, or Sound Transmission Class, introduced in 1970 as ASTM E413, is a value based upon the attenuation that is required to reduce each octave level of the noise spectrum to match the NC-25 contour. This is a weighting method that is designed to compare the relative attenuation of fenestration systems of office type noises (speech, radio, television and similar noises).
STC is affected by glass thickness, air infiltration, air gap, type of glass (annealed vs. laminated), type of spacer (non-metal spacers are quieter), the use of insulating glass films, argon filling, edge dampening and the use of dissimilar materials to break up harmonic waves.
Laminated glass is one increasingly popular way to improve sound reduction, with additional benefits such as improved security. There are specific interlayers that can be used to absorb sound waves. Also, by combining glass lites of dissimilar thickness within the IG unit, sound transmission can be reduced by preventing the buildup of harmonic waves.
Oftentimes, architects are faced with a project which entails installing windows with a minimum STC (Sound Transmission Classification) value. This might be dictated by a building code or simply specified by the building owner. But today’s forward thinking architects are now digging deeper into the data as opposed to just looking at the single number rating systems such as STC or OITC (Outdoor Indoor Transmission Classification) numbers. They appreciate the knowledge that certain materials or technologies might reduce sound transmission across a specific frequency range even though the STC value might not change at all.
For example, argon gas filling might be used to reduce sound transmission across the bandwidth between 500 to 3000 Hertz, without changing the STC value at all. If one looked only at the STC values, the conclusion might be drawn to promote only the thermal performance attributes of adding argon or to abandon gas filling altogether. But by digging deeper into the data, a savvy architect may find that improving sound control in this specific frequency range could have a significant impact in terms of blocking out the sound of car horns in urban areas. Yes, we can actually fine tune a window to absorb specific frequencies bases upon the environment surrounding the location in which that window is to be installed!
Technologies for designing windows for improved sound control are likely to become increasingly important as our nation grows and we population density increases.
So, when it comes to sound control in window design, excuse the pun, but “stay tuned” for new developments!
Editor’s note: DWM is working on an article on how to market acoustical products to homeowners. If you have knowledge to share post a comment here or email firstname.lastname@example.org.