Noise Buffers
by Marie Hofer, Gardening editor, HGTV.comGardens are all about nature and less about man-made noise, right? When Thoreau spent two years on Walden Pond, his nearest neighbor was a mile away. He could hear traffic on a distant road and a railroad track, but the sounds of it didn't interfere with his hearing geese flap their wings overhead or the ground crack during a freeze. That was then and this is now. Today the average garden is more apt to share air space with the sounds of steady traffic, neighbors' lawn mowers and string trimmers. It's one thing to create privacy in the garden; the right plants, a fence or a vine-covered trellis, and you've got it. It's another thing altogether to dampen noise. Unlike light waves, which travel in straight lines, sound waves bend around obstacles.
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Letting plant material cover walls helps a little in reducing echoes, and it also enhances the wall's attractiveness, giving it a timeless look. The thicker the layer of plant material, the more noise buffering you'll get.
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Plants don't really do the trick. Fleshy-leaved plants such as hollies are better at reducing sound than even dense-needled evergreens, but that's not saying much. Most experts agree that you'd have to have at least a 100-foot-wide border of dense plantings to see any real effect on noise levels. Instead, the chief value of plants in this context is to block the sight of the noisemakers, which often takes care of part of the problem, at least psychologically.In Silicon Valley, Calif., sound issues are a "very big deal," says landscape architect Thomas Klope, ASLA. "We don't rely on plants to attenuate noise. Instead we opt for physical structures like masonry walls. Then we might use a very thick vine over the wall--a very dense mat of plant material such as creeping fig." A thick layer of plants helps to soften echoing. Another approach that Klope likes to use is a conventional double wood fence with a "sonic barrier" suspended between the panels. The material is a special high-density vinyl that hangs free and invisible between the panels. The material must hang limp and can't be stretched, so that it's free to vibrate. A cap is placed over the two panels of the fence and all the crevices caulked to prevent ultraviolet light from deteriorating the barrier. Suppliers of the vinyl barrier estimate that such a fence, built eight feet high and positioned 16 feet from the noise source, can block 25% of that noise as measured at a distance of 64 feet away. The following is a step-by-step illustration of the double-fence and sonic barrier construction. In this case, the vinyl barrier has been extended below the level of the fences so it can do double-duty as a termite blocker:
As anyone who has ever walked to the other side of a hill knows, soil is a great sound buffer.
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Still another good sound reducer is the earth itself--chiefly berms, or strategically placed banks of soil. The western edge of the Chicago Botanic Garden borders the Edens Expressway, and the steady roar of traffic has been a common complaint of visitors to the garden. Next year visitors will hear less noise and they won't see the traffic, thanks to the combination of a giant berm-plus-wall that's being created along the 1-1/4-mile boundary. On the traffic side of the berm and wall, thousands of new plantings will give passersby something pleasing to look at and will essentially add another garden to the 23 that are already on the site.If you'd like to reduce sound in your landscape, here are more tips from the experts: A lot of variables affect how much noise you hear--grade differences and distance between you and the noise source, the size and distance of other structures, etc. Before you commit to a major construction project, consult an acoustical engineer for advice on what will work best in your landscape. If you're planning to use a landscape architect, you can typically expect that such an engineer will be consulted. Even a berm of only three to five feet can have some impact on noise reduction, depending on the position and distance of the noise source, the berm and your garden or house. Make the berm as natural-looking as possible, shaping it so that it appears to fit with the landscape. "The last thing you want it to do is look like a bump or an elephant under the rug," says landscape architect and author James van Sweden, FASLA. "It has to look like it's grown out of the landscape, that it belongs in the neighborhood. You want to mold the land so it's beautiful." Plants on top can help it look more natural and also create privacy. Add a water feature. The sound of running water does wonders for masking traffic noise, and landscape designers and architects all over the country use it. "Even in [Washington] D.C.," says van Sweden, "a fountain can help mask the sound of planes."
Resources Chicago Botanic Garden berm project
Website: www.chicagobotanic.org/bermArchitecture in the Garden
by James Van Sweden, Thomas Christopher (Contributor), Penelope Hobhouse
Random House, 2003
Order this title from the HGTV.com store. Landscape architectsMarshall, Tyler, Rausch
101 Bellevue Road
Pittsburgh, PA 15229
Phone: 412-931-6455
E-mail: mtr@mtrla.com
Website: mtrla.com
Prospec Non-reinforced Barrier
John Strandberg
Chemical Engineer
West General Acoustics
Website: www.westgeneral.com/products/illbruck_prospec_barrier.html Guests Thomas Klope, ASLA
Landscape architect
Thomas Klope Associates
Los Altos, CA
Phone: 650-941-9162
Fax: 650-941-9304 | |
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