FAIRHAVEN – “You can hear them pulsing tonight.”
It’s midnight on Shawmut Street, and the southwesterly wind makes the location “an optimal spot for sound testing” Fairhaven’s turbines, said Laurel Carlson, a technician with the state Department of Environmental Protection.
In front of her is a sound meter. Roughly 7 inches long, it’s shaped like an oar, with a foam ball at the skinny end protecting the microphone that points diagonally up toward the turbines. The meter’s buttons glow in the dark. It sits on a tripod on the lawn overlooking the wetlands that reflect the light of the full moon.
Above the marsh, turbine blades spin, glowing orange from lights on the nearby radio tower.
On the ground, the wind is blowing 2.3 meters per second. At the hub of the turbines, it blows 6.5 meters per second.
“Three, two, one, go,” Carlson says, and the sound sample begins.
With her is Fairhaven Wind Developer Sumul Shah, who watches a graph on his laptop showing the turbines’ power output. The computer records second-by-second data for wind speed and power output that will be compared with the noise data later.
Both Shah and Carlson are wearing headlamps, and her light bobs up and down as she looks from the meter to her clipboard, where she writes down the decibel levels.
Every five seconds over the course of five minutes, she records the numbers: 47.8, 46.6, 47.7, etc.
The whooshing of the turbine blades is distinctly audible over the breeze and the crickets. Every so often, Carlson shakes her head, and writes the letters “G” or “C” to show when gusts of wind or car noises interfere with decibel readings.
“Well, we had some interesting noises on that one,” she says after five minutes have passed.
Early morning Friday was the second round of testing Carlson has conducted on Fairhaven’s two wind turbines. Her goal is to assess whether the noise made by the turbines is 10 decibels louder than Fairhaven’s ambient sound, which would put them in violation of Massachusetts’ noise regulations.
“Ten decibels is the difference between a dishwasher in the next room over from you being on or off,” Carlson says. “Some people think the 10-decibel regulation is too high, some think it’s too low. All I know is it’s my job to see if it’s above or below that.”
Carlson takes three five-minute-long samples of noise with the turbines on, then tells Shah to shut the turbines down so she can repeat the process. Over the course of the night, she will take a total of 18 samples; 12 at two locations at this address and six at one on Teal Circle. Carlson needs six to eight nights of testing for the sound study to be complete, but depending on wind conditions that could take months, she says.
On his Dell laptop, Shah clicks a button labeled “Stop.”
“Do you really want to stop the turbine?” asks a popup on his screen.
He clicks “Yes,” and the turbine blades slow as the line on his computer measuring their speed falls. It all takes about a minute to completely shut down before Carlson can take more samples.
Noise sampling for wind turbines is a delicate task, Carlson says. Thursday night’s visit to Shawmut Street is actually meant to make up for testing Carlson conducted there three weeks ago when a single cricket skewed the results of an entire hour’s worth of testing.
“It was just one bug, but it was too close to the meter,” Carlson says.
Assuming the insects cooperate, the testing has to be conducted when the wind is at specific speeds and directions.
Falmouth’s turbines were the first Carlson ever tested. She says she usually takes noise samples for industrial facilities, checking to see if HVAC units or gravel pits are too loud.
“That stuff, any time of day will do, and most of the time you want no wind,” says Carlson, who usually works from 7 a.m. to 4 p.m. at the DEP.
“The thing with turbines is that their sound proof changes as the wind speed changes – you have to be out in the middle of the night,” she says at 1:30 a.m. Friday as she packs up her gear to move from Shawmut Street to Teal Circle. “It all depends on the wind.”
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