Infrasound is sound with a frequency too low to be heard by the human ear – in general it is bass waves with a frequency below 20 Hz to 22 kHz.

We are surrounded by and have evolved within an environment of naturally occurring infrasound — ocean waves, wind, earthquakes, pounding surf, waterfalls, hurricanes, thunderstorms, and anything that produces a naturally occurring slow oscillation of the air.

And of course, there is a whole lot of human generated infrasound – from slow speed fans to engines, cars, buses, trains, motorcycles, airplanes, explosions, and machinery.

Yet the fuzzy connection between wind turbine infrasound and risk to human health continues. It hinges on the idea that high levels of low frequency noise excite the body to vibrate, most notably in the chest, and that profoundly deaf humans perceive noise through vibrations in their bodies. But the thinking is circular to claim that wind turbines generate inaudible infrasound that “can be felt but not heard” and that this infrasound vibrates the chest with dire health risks.

To begin with, the noise frequency levels that produce body vibrations are well above the hearing threshold. You would hear the explosion, crash, or band speakers cranked to their maximum loudness as well as feel them, unless you were profoundly deaf. So the idea that unperceived wind turbine infrasound is pounding your body and making you sick – is another one of those “we don’t want wind turbines” myths.

On the other hand the “problem noise” that does come from wind turbines is the fluctuating swish sound of the blades passing the tower, which does irritate some people who are highly sensitive to fluctuating sound.

The problem is that wind project objectors use acoustic terms like infrasound incorrectly. They indicate that ‘infrasound’ is a generalized health problem for all people living near a wind turbine. It is something they cannot hear, but they can all feel it and that their health is at risk.

What we do need to note is that the turbine swish noise might be problematic for some people and when those affected by fluctuating sounds appear, we do need to pay attention. But if scores of people in an area start claiming that the blade swish sound is affecting them negatively – be skeptical. Intermittent sound fluctuation really only affects some very sensitive people – not everyone. It is a real problem – just not a really pervasive one.

For more on the infrasound and turbine issue, click here:
Infrasound from Wind Turbines – Fact, Fiction or Deception by Geoff Leventhall.

And click here for:
Do wind turbines produce significant low frequency sound levels?  by G.P. van den Berg

Click here for information on tubine noise assessments in other posts on my site:
A sound by any other name…

Special thanks to Appalachian State University for publishing the Leventhall and van den Berg papers in the Reports section of its very informative website.

Then along came SWIFT.

“The SWIFT Wind Turbine design solves many of the challenges of previous residential and commercial scale wind turbines: it registers as a whisper on decibel charts, it’s efficient, it’s safe and it’s clean,” states Cascade Engineering’s Michael Ford, on their new SWIFT Wind Turbine system.

Available in the US and Canada, the SWIFT Wind Turbine system provides businesses and homeowners an effective solution to lower energy bills and reduce carbon emissions. The unique design of the SWIFT system lies in the outer ring that connects to the turbine blades. As the wind travels down the blades and is dispersed along the outer ring, the outer ring acts as a diffuser eliminating noise and keeping the turbine quiet.

It is the first very quiet rooftop mounted wind turbine for domestic, community and industrial use. And it generates electricity by harnessing wind energy both quietly and safely. The SWIFT Wind Turbine incorporates safety features that meet IEEE safety standards and has achieved the Underwriter Laboratories (UL) certification by MET Laboratories, Inc., a global symbol of safety.

Optimally sited this turbine will produce approximately 2000 kWh of electricity per year in a good wind location. This is about 20% of an average home’s needs. The initial cost of $10,000 to $12,000 per system can generally pay for itself in about 3 years and multiple units can be used at one location to supplement industrial and commercial needs. The SWIFT system has a 5 year manufacturer’s warranty and is designed for a 20 year life.

Click here for more information.

The SWIFT Wind Turbine has been designed to be environmentally sustainable. The product produces more energy in its lifetime than is incorporated in the material and processes used to manufacture it – it is therefore “harm neutral.”

Seeing his small turbine as no more obtrusive than satellite dishes that do not require permits, and fully expecting the government to soon scrap permit requirements for all home green-energy sources, Phil Proffitt, did not apply for planning consent.

He may be right. In March 2008, permit rules changed. UK householders can now install solar panels and heat pumps and other such energy generators on their houses without permits, but wind turbines were excluded. Resistance focused on the turbine noise and vibration issues.

So, Mr. Proffitt, may have to take down his turbine and apply for a wind turbine permit. His neighbors are watching this case very closely – supporters, resistors, and those in between.

Looking at his house-attached turbine, Mr. Proffitt says, “They are no more obtrusive than big satellite dishes – people used to complain about TV aerials in the 40s, and then it was satellite dishes, and now a few people will complain about this.”

Click here for the rest of this neighborhood wind energy story.

Noise was a very serious problem for the wind energy industry back in the 1980s. Some early turbines were so noisy that even from a mile away it was often annoying to hear them. But today, “an operating wind farm at a distance of 750 to 1,000 feet is no noisier than a kitchen refrigerator or a moderately quiet room.” (American Wind Energy Association)

Well-designed wind turbines are generally quiet in operation. When compared to the noise of traffic, trains, aircraft, industrial and construction activities the noise from wind turbines is very low. And since the 1980s, turbine manufacturers have done a great deal to reduce wind turbine noise.

How noisy are wind farms today?
Compared to other types of industrial and commercial facilities, wind farms are very quiet. But their location in rural, rather than more noisy urban areas gives them less ability to blend into the area’s background “white noise.” On the other hand, most wind farms are located where the wind speed is higher than average. High wind itself will mask the sounds of turning blades.

However, if you are looking to site your turbines in hilly terrain where nearby residences are downwind in shallow valleys, dips or hollows, turbine sound may be an issue. Turbine noise may carry further and not have the high wind “white noise” to mask it as you would find on flat terrain. So, choosing the best site for project turbines becomes an even more important issue.

How noisy are small wind turbines?
Small wind turbines tend to be noisier for their size than large turbines. The manufacturer can provide information about its noise levels, based on standard measurement techniques. Most communities have noise ordinances that typically specify an allowable decibel level for noise at the property line nearest to the source. So, again before you launch into a wind project, there is a lot of homework you need to do.

To address “noise issue” resistors, your best bet is to have a noise analysis conducted as early as possible in your project planning.

A noise analysis will assess:

• Operating sounds of the specific wind turbine that will be used
• The topography of the terrain where the project will be located
• The distance to nearby residences from the wind turbine(s) site
• Where residences are located relative to the wind blowing across the terrain
• If any residences are sheltered from the wind (and the natural sound it produces)
• The normally-occurring background noise levels at the site (pre-construction)

“The most common method for dealing with a potential noise issue is to simply require a “setback,” or minimum distance between any of the wind turbines in the project and the nearest residence, that is sufficient to reduce the sound level to a regulatory threshold.” (American Wind Energy Association “noise facts” ).

“In general, wind farms are not noisy, and wind is a good neighbor. Complaints about noise from wind projects are rare, and can usually be satisfactorily resolved.”