Yard Noise-Reduction

Out of Sight, Out of Mind

Along the road in front of the Carlisle house, young disease-resistant elm trees will sit where a couple of older trees had once flourished but had fallen prey to disease in the last century. In the backyard, multistemmed Heritage river birch will replace old, dying hemlocks along the property line, and also in clusters at the outer edges of the yard to buffer it from some of the noise filtering in from the adjacent streets.

Many homeowners consider using plantings like these to block noise from their property, but in fact, greenery has very little effect on noise levels (though rustling leaves can be another source of white noise). The problem is those persistent sound waves, which sneak through the tiniest openings. You'd need a tree swath at least 50 feet deep to get good sound absorption.

But because sound perception is highly subjective, sometimes our brains can be tricked. The field of "psycho-acoustics" is a recent area of study — though its effects have been observed for many centuries. Four hundred years ago, when European church organists couldn't reach all the right pedals, they realized they could play a combination of notes that made people think they were hearing a much lower note. Today, some small speakers digitally enhance similar frequencies to create a "phantom bass" effect, making these same components sound like much larger models.

Psycho-acoustics also connects aural and visual stimuli. "Certainly out of sight is out of mind," says engineer Jim Barnes, who works with Wood at Acentech. That's why plantings create a perceived reduction in noise, even if a decibel meter says otherwise. "As an engineer, I do like to quantify," says Barnes. "But if people say 'Yeah, it's much quieter,' I take them at their word."

Roger Cook sees it all the time. "Greenscaping that blocks the view of the noise's source will always make a property more comfortable," he says. "Even a nice lawn will make you feel farther from the road." When designing landscapes for acoustic comfort, Hubbard suggests including evergreens for their year-round leaf structure. Among her favorites are Hetz wintergreen arborvitae, a narrow tree good for small spaces; Colorado spruce; and Hinoki cypress.

Such greenery can also soften the monolithic look of a noise-blocking fence. "Plantings create some visual interest and break up the hard line," says Hubbard. Along the wall at Carlisle, hydrangeas, lilacs, and spirea will accent the stone with seasonal flowers and foliage, while a boxwood hedge that will grow to 6 feet will increase the sense of separation from the road.

But it's the backyard that will provide the most tranquil retreat. There the grounds are inherently quieter, shielded from the main road by an acoustic barrier that's better than any fence or fountain: the newly restored house itself.

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