Wind Turbine Sound
Depending on the site, proximity to nearby residences, and the permitting regulations, wind farm developers are typically required to address potential sound issues in the permitting process and must demonstrate that the project will comply with the applicable sound level regulations.
In most cases, acoustic modeling is performed before and after a wind project is constructed to ensure that residents in proximity of a wind turbine experience sound below the appropriate thresholds.
Turbines can create two types of sound: a mechanical hum produced by the generator and a “whooshing” sound produced by the blades moving through the air. Modern commercial turbines are designed so that the turbine is upwind of the tower, which mitigates low-frequency and impulsive sound. Turbine and tower design can also affect sound output.
Although research to develop sound mitigation techniques is ongoing, as of 2013, global peer-reviewed scientific data and independent studies consistently concluded that sound from wind plants has no direct impact on physical human health. Read more about potential health and safety concerns.
Types of Wind Turbine Sounds
Wind turbines make different types of sound, including broadband, infrasonic, impulsive, and tonal sound. The presence of wind turbine sound is dependent on atmospheric conditions, including air flow patterns and turbulence, and the ability to perceive wind turbine sound varies based on the presence of other nearby sources of sound, manmade or otherwise, and site-specific topography.
Because wind turbine sounds are specific to their environments and it is difficult to re-create sound levels that may be heard at a proposed wind project, people are strongly encouraged to visit an operating wind farm to better understand potential sound impacts.
Broadband sound is made up of a combination of sound waves with different frequencies. It has no distinct pitch and could be described as a humming, whooshing, or swishing sound.
Infrasonic sound is always present in the environment. Depending on the locations, examples include the sound of flowing water, waves, or air turbulence. It can propagate further than higher, more audible frequencies, but it blends in with ambient noise. Although infrasonic noise is often inaudible, it can cause structural vibration, such as windows rattling.
Impulsive sound can be generated when disturbed airflow interacts with turbine blades, making swishing noises. Impulsive sounds can vary in amplitude over time. Examples of impulsive sounds include a door slamming or a person stomping.
Tonal sound can be caused by the rotation of shafts, generators, and gears operating at natural frequency; unstable airflow over holes or slits; or non-aerodynamic instabilities interacting with the blade surface. Tonal sounds can have a distinct pitch, such as a music note, and do not start or end abruptly. Because tonal sound can be problematic, wind turbine manufactures are paying particular attention to addressing tonal sound produced by their turbines.
Methods for Sound Mitigation
Various methods are used to manage or mitigate the potential impact of wind turbine sound, including:
- Understanding and documenting potential turbine noise during the project development stage
- Maximizing the distance of wind turbines from nearby inhabited buildings or property lines
- Conducting studies to ensure that turbine sounds and background noise do not surpass the Environmental Protection Agency sound guideline of 55 decibels for outdoor sound
- Creating “sound easements” on adjacent property that give the developer the right to generate sound carrying over onto that property
- Changing turbine operating modes depending on wind conditions
- Sharing of some portion of landowner royalty payments with affected neighboring landowners.
Small Wind Turbines and Sound
Most modern residential wind turbines create sound that is only slightly above the ambient wind noise. Under most wind conditions, a small wind turbine that meets certification requirements does not create a significant amount of noise.
- Predicting Audibility of and Annoyance to Wind Power Project Sounds Using Modeled Sound
- Understanding the Impacts of Wind Turbine Sound: A NEWEEP Webinar
- OpenEI: Sound
- Wind Turbines Noise and Health: Fact vs. Fiction Simulcast: A NEWEEP Webinar
- Massachusetts Department of Environmental Protection, Massachusetts Department of Public Health: Wind Turbine Health Impact Study - Report of Independent Expert Panel