Acoustic Profiling of Infrasound and Audible Emissions from Wind Turbines: Field Measurements in Northern Sweden 

Wind turbines produce both audible noise and low-frequency infrasound (below 20 Hz), which, though often inaudible, may have physiological and psychological effects that require further investigation.

Previous studies confirm that wind turbines are significant sources of both audible and infrasonic noise. Infrasound is primarily generated by blade-tower interactions and atmospheric turbulence. Sugimoto et al. demonstrated a strong correlation between infrasound levels and rotor speed, highlighting the need for sensitive measurement systems capable of detecting frequencies below 1 Hz. Pierzga and Boczar analyzed infrasound emissions from low-power vertical-axis wind turbines (VAWTs), showing notable impacts even at smaller scales. Similarly, Malec and Boczar examined high-power horizontal-axis wind turbines (HAWTs), finding that infrasound emissions vary with wind speed and are influenced by resonant and median frequencies.

Despite growing awareness, standardized methods for measuring and evaluating wind turbine infrasound are limited, particularly in non-industrial settings. Further research is essential to characterize these emissions and inform guidelines for wind farm development.

This study presents a comprehensive analysis of infrasound and low-frequency acoustic emissions from high-power HAWTs at four wind farm sites in northern Sweden: Bergvind Lingbo, Vindpark Jädraås, Hästkullen, and Björnlandhöjden. Located in the municipalities of Ockelbo and Härnösand, these sites vary in scale and operational status, comprising 41 to 73 turbines and annual energy outputs ranging from 590 to 1,051 GWh. Field measurements employed a dual-microphone setup using a Lidström infrasound microphone, optimized for detecting acoustic signals below 20 Hz, alongside a ZealSound USB condenser microphone for audible frequencies. This configuration enabled the simultaneous capture of infrasound and audible noise data, supporting detailed spectral and time-frequency analyses. Measurements at four wind farm sites show that infrasound levels are notably higher compared to a reference site without turbine activity. Recordings were conducted both outdoors and inside a stationary vehicle. In addition to elevated infrasound, broadband audible signals were observed, linked to blade swishing and wind interactions, producing harmonics and turbulence-related features.

Conclusions

Using simultaneous measurements with a Lidström infrasound microphone and a ZealSound USB condenser microphone, the research highlights the presence of infrasound components below 20 Hz and the characteristic swishing sounds within the audible range.

The comparison between outdoor and in-vehicle infrasound measurements across all sites indicates that while the vehicle provides measurable infrasound attenuation, it does not fully shield the interior from external low-frequency noise. The reference site data validate that the elevated infrasound levels observed at wind power sites are not part of the natural background, strengthening the conclusion that wind turbines significantly contribute to infrasound in the surrounding environment. These findings support the notion that infrasound exposure may persist even in enclosed spaces such as vehicle cabins, warranting further investigation into its transmission dynamics and potential health implications These findings contribute to a better understanding of the acoustic environment surrounding wind turbines and provide valuable data to inform future research, standardization efforts, and policy development for sustainable wind energy deployment.

The audible spectral measurements from all four wind farms reveal broadband acoustic signatures that span the full range of human hearing. The spectral shapes vary by site, possibly due to differences in turbine models, layout, topography, wind conditions, and measurement positions. These findings reinforce the need to consider the full audible range—not just tonal components or low frequencies—when assessing wind turbine noise impact and designing mitigation strategies.

Per Ängskog, Department of Electrical Engineering Mathematics, Kourosh Tatar, Department of Industrial Management, Industrial Design and Mechanical Engineering, José Chilo, Department of Electrical Engineering Mathematics, University of Gävle, Sweden.

11th International Conference on Wind Turbine Noise, 10th to 13th June 2025

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