Science: Noisy Windmill

Shushing the swish-swish

The world's largest windmill began operating last year in Boone, N.C. With blades that stretch 60 meters (200 ft.) from tip to tip and can generate 2,000 kw of electricity, it is also, it seems, the world's noisiest. Besides dominating the scenic Blue Ridge Mountains landscape—or despoiling it, as some of those living near by complain—the monster rattles windows, bounces cups and saucers and creates an irritating swish-swish.

Surprised by this unexpected noise pollution from an experimental power plant that was supposed to be almost entirely free of environmental headaches, engineers from the U.S. Department of Energy and NASA flocked to Boone (pop. 8,754). Their findings: though the very low-frequency sound waves (about 2 cycles per sec.) from the windmill are below the usual range of human hearing, they can be amplified by wind and weather conditions and the terrain over which they are directed and thus become powerful enough to vibrate objects in the home.

Muffling the wind machine may force a major retooling of the $6 million project, including a change of blades and electrical generators to allow for slower rotation. It may also require a reorientation of the basic design, so that future windmills face into the wind rather than away from it. Meanwhile, the Department of Energy has given Boone some temporary relief. Until some way can be found to hush the noisy blades, they will no longer be allowed to whirl at night, in the early morning or on weekends. ∎