The sound of a wind turbine

The sound from modern wind turbines has unique characteristics that distinguish it from other environmental sounds. When the rotor blades pass the tower, pressure changes create a characteristic pulsating sound, known as amplitude modulation. This rhythmic variation makes the sound particularly noticeable because the human ear is developed to detect precisely such patterns, even when the total sound level is relatively low.

The size and height of wind turbines create significant low-frequency components in the sound. These low frequencies have the ability to travel long distances with minimal dampening from the atmosphere. When the sound reaches buildings, the low-frequency components can penetrate walls and roofs in a way that higher frequencies do not. Once inside the building, the sound can be amplified through room resonances, where the room’s dimensions interact with the sound’s wavelengths. This can create standing waves and amplification effects that make the sound experienced differently in various parts of the same room.

The atmospheric environment plays a crucial role in how wind turbine noise propagates. Temperature stratifications in the air can create sound channels that carry the sound further than expected. Wind gradients – how wind speed changes with height – can bend sound waves downward and create areas with enhanced sound far from the source. This explains why the sound can sometimes be heard clearly at great distances while at other times it is barely noticeable much closer to the turbine.

A particularly complex phenomenon is sound masking. Under certain wind conditions, wind turbine noise is masked by natural wind noise from vegetation and terrain features. Paradoxically, this can mean that the sound is perceived as more disturbing at moderate wind speeds than at high speeds, because the masking effect is then less effective. This effect is enhanced by the fact that modern wind turbines begin to rotate at lower wind speeds than older models.

The constant presence of the sound constitutes yet another dimension. Unlike many other sound sources, wind turbines can be active around the clock, for weeks at a time. The long-term exposure, especially at night when other sound sources are quiet, can affect how the sound is experienced. While the sound level varies with wind speed, the rhythmic character and low-frequency components can be noticeable even at low total levels.

These acoustic properties mean that traditional measurement methods and comparisons with other sound sources often become misleading. A-weighted sound level in decibels (dBA) does not capture the pulsating character or the low-frequency components in a fair way. This explains why the sound from wind turbines can be experienced as disturbing even when measured sound levels are below recommended limit values.