Lake Township officials are considering what information is important as they draw up a wind turbine zoning ordinance. After a nearly two-hour presentation from Dr. Malcolm A. Swinbanks, M.A., PhD, applied mathematician, acoustician and consultant engineer, the board decided to conduct a work session to further discuss the matter. During the presentation, Swinbanks gave information primarily on noise levels.
Ordinances allow for how much noise a turbine can make. Swinbanks explained that noise is made up of many frequencies, and low-frequency noise is outside the range of human hearing. While people cannot hear low-frequency noise, it can impact a person’s health. Unfortunately when measuring turbine noise, Swinbanks said, ordinances typically put more restrictions on noise within the human hearing range and do not restrict low-frequency noise enough.
He said that low-frequency noise from turbines is not constant but repetitive and like that of a person hearing a passing siren. He said that current research is looking at the effect of low frequencies on the cochlear area in the ear and the body’s balancing mechanisms.
Another factor which can be considered is ambient noise.
Swinbanks explained that ambient noise is the irreducible residual background noise that is always there and that ambient noise levels are higher in the city than in the country. He said that the ear of a person in the country may be accustomed to lower ambient noise levels. He gave the example on how the eyes adjust to low or high light levels. He also said that the ear processes high and low sound frequency differently and might ignore high frequencies more than the low ones.
Swinbanks said it makes more sense to him for an ordinance to be strict in regard to property use and noise levels and allow for variances rather than having a permissive ordinance.
He also said he feels turbine setbacks should be from the edge of the property and not from a residence. He explained that this could create an easement, in effect, on a neighboring property and might preclude a neighbor using their property for some uses.
During the presentation, Swinbanks said that a study by Michigan State University in the 1970s said 55 decibels at a property line for three minutes would be acceptable. He said one reference in the study said levels above 45 decibels caused annoyance and another reference to a rural study said above 35 caused annoyance. He said that it is generally accepted in the international community that levels above 40 decibels at night may cause problems.
In other business, the board discussed matters related to sand mining, and ordinances relating to lighting and outbuildings. The board decided to look into these matters and tabled them until the next meeting.