Quiet-seeking residents just grit their teeth and wait it out: the small construction site, the outdoor community event blasting music, the road crew tearing up the street with a jackhammer. These instances tend to be too modest to warrant the expense and hassle of cement walls.
But relief could come from a mobile, inflatable layered noise protection system.
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"If you have a temporary noise source, like a construction site or an open-air event, nobody is erecting a concrete noise barrier," said Philip Leistner, a professor of acoustics who teaches at the Fraunhofer Institute of Building Physics and the University of Stuttgart. Leistner and his colleagues at Fraunhofer developed the unique technology to contain blaring outdoor sound.
Leistner said he and his colleagues questioned the prevailing opinion that thin films and membranes were too light to provide significant protection from noise. After the Germans did their own in-depth study, they concluded that a double-layer of membrane with the right distance between the layers could be acoustically comparable to a concrete barrier. The trick was getting the right distance, and making the solution high enough to block sound.
The Fraunhofer system consists of a two-layer special textile coated in plastic and heat-sealed to make it airtight when inflated. The textile contains wire-like pieces of fabric in a random pattern. The final inflatable barriers have roughly six inches of space between the layers. Each wall rises approximately 11 feet and spans about 14 feet.
According to the institute, the system provides an insulation of 17 to 20 A-weighted decibels, a common environmental noise measurement. Leistner said the Franhofer system is as effective as existing movable sound screens but much easier to handle.
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Inflating or deflating takes about three minutes with a vacuum and, when not inflated, each 88-pound wall can be folded for transport. The surface could be used to display temporary artwork or advertisements, Leistner said.
"Because of the temporary character of the noise, the companies or the users only need these elements for a certain period," Leistner said. "A renting system would be nice."
Fraunhofer's patented production process has been licensed to the Germany company Ceno Tec, which is making the inflatable barriers. Leistner said that there is a demand in Germany at construction sites for this kind of temporary equipment.
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The noise protection system was displayed last week at the UrbanTec Trade Fair in Cologne as part of Fraunhofer’s vision for the city of the future, "Morgenstadt." Next, Leistner and his colleagues are developing noise-blocking mobile barriers that are translucent so that construction workers could get natural light even when enclosed by the system.
Ning Xiang is a professor of electrical, computer, and systems engineering at Rensselaer Polytechnic Institute who attended the Fraunhofer Institute of Building Physics and knows Philip Leistner well. Xiang wanted to be clear that he is not endorsing the Ceno Tec barrier and he hasn’t seen all the data on the technology’s performance.
"What's intriguing in this technique is the lightweight portability, it's a kind of flat balloon," he said. "You just can put it up so easily." Achieving results comparable to concrete barriers would be amazing, he added.
Nancy Timmerman, a Boston-based acoustics and noise control consultant who has worked on minimizing outdoor noise, compared the Fraunhofer system’s weight to a mineral-filled visco elastic sound-blocking material made by the Tampa-based company Acoustiblok.
Based on Ceno Tec’s data sheet, she expects the material will provide a modest reduction in sound. "The sealing of the gaps between the panels, in the temporary service contemplated, must be airtight and easy to accomplish or the performance will suffer," she added.
Michael Ermann is an associate professor of architecture and design at Virginia Tech who is co-authoring a new edition of an architectural acoustics book and just wrote the section on noise barriers. Ermann called the Fraunhofer system interesting technology that’s “a really good idea in some ways,” but wonders how effective it is at blocking low frequencies, particularly the bass tones generated at construction sites.
One of the biggest factors in community noise complaints is whether residents feel like those in charge are making a good faith effort to keep the volume down, Ermann said. "It's not really enough just have barriers."