Measuring decibel levels is extremely important, as it is an objective way to compare the sound to everything else around us.

You may have seen this nifty diagram released by GE last week:

As you can see, a large wind turbine isn't very loud from an objective standpoint. According to this data, at a very close distance of 300 meters away, a turbine will be somewhere between an air conditioner (50 decibels) and a refrigerator (40 decibels). At about 500 meters, the levels drop to about 38 decibels, which is well below the typical 40-45 decibels of background noise in a populated area.

So if wind turbines aren't any louder than what we're already used to, why are some people complaining about them?

It comes back to subjective factors that decibel measurements don't account for.

The quality of wind farm noise is one factor. Researchers are looking at whether the low-frequency woosh, woosh, woosh of blades has a different psycho-social impact than noise from highways or airports. It's very common that people living close to turbines call the sound “penetrating.”

Of course, different people handle the sound in different ways. Many residents are unfazed by turbines at close distances. Others find them unbearable. For a developer, reaction to a project depends on what kind of people you have living in close proximity to the machines.

The other major factor is communication. If a developer doesn't accurately describe how sound levels or sound quality may change, the potential for backlash becomes far greater. For example, a handful of residents living near three GE 1.5 MW turbines on the Maine island of Vinalhaven say that the developer, Fox Islands Wind, mislead residents about sound levels. A lot of the outrage (which has gained national media attention) was over poor communication about how the turbines would impact the soundscape of the rural island.

Clearly, these highly-variable factors are just as important as objectively measuring decibel levels.

 

Comments:

A key part of this graphic that most people will not appreciate is the "A" after dB (i.e. dB (A)). This means that all the infrasound (< 20 Hz) generated by the turbine, which undoubtedly affects the ear at levels below those that are heard, is totally ignored by the measurement. This measurement is equivalent to considering only the visible portion of sunlight and concluding that sunlight cannot harm you. We all know that the invisible portion of sunlight (the ultraviolet light) is the portion that causes skin and eye problems. Similarly, it is the unheard infrasound component of wind turbine noise that causes problems to nearby residents. Until the industry starts taking note of this, the problem of wind turbine noise on nearby communities will not be solved. Long term infrasound exposure disturbs sleep and this graphic completely ignores this fact. So it may be a clever graphic, but it misrepresents the true (infrasound-dominated) nature of wind turbine noise.

A couple other important factors: even within audible sound ranges, the sound spectrum of wind turbines is heavily weighted toward the lower frequencies. Turbine noise is often clearly of a lower overall frequency than the ambient noise in bushes and trees; this is one reason it is not as effectively masked as often is assumed.

Perhaps the most important metric is whether the turbine noise is more than 5dB above the background ambient (in the moment; averaging sound over time can miss the fact that for parts of a day and especially night, ambient noise is lower than an averaged level). As it moves past 5dB over other sounds, it becomes distinguishable; as it reaches 10dB over other sounds, it will be readily noticeable and likely to cause some annoyance. 15dB or more is quite intrusive.

Expectations are obviously crucial, as noted here. If peace and quiet is a prime reason many people in the area live there, then any audible intrusion from large industrial installations will trigger discontent. If most everyone nearby is more actively working the land and using machines in their daily life around their land/ranch/farm, then it's probably going to be less of an issue to hear turbines added to the mix at the low level they are heard.

The GE chart appears to be a relatively best-case scenario; I'd be interested to know what noise attenuation assumptions are behind it. It's quite common to see noise maps that predict 40dB levels at much more than 400m (eg, a map in Ken Kalinsky's NEWEEP webinar last July shows 40dB at locations 1800-3700 feet from turbines, and 45dB at locations from 1700-2900 feet; note: estimated using blown-up copy and distance scale on the map). Such maps, as well as repeated reports from neighbors, suggest that turbines can be audible to over a half mile, and at times to a mile.

Finally, the subtle pulsing nature of the sound, especially when several turbines are audible with differing peaks, can be quite disconcerting or disorienting.

In general, people do not live close to nuclear reactors or to coal fired plants, either. While the problems associated with wind turbines, solar farms, geothermal sources or ethanol plants may be more benign than the problems associated with older power plants, we should not be surprised that there are still some minor problems with alternative energy plants.

The vibrations (aka "noise") from a wind turbine may be much less harmful than radiation from a leaking nuclear reactor, but it is still a nuisance.

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