Can wind turbine sound that is below the threshold of hearing be heard?
Paul Schomer|June 1, 2013
This paper by acoustics expert, Paul Schomer, explains how noise at very low frequency levels can be heard. The fundamental issue is: Can we hear slowly surging or pulsating sounds for which the LEQ spectrum is below the threshold of hearing, where "slowly" means that the pulses come at a rate that is no faster than about 4 pulses per second? The short answer is yes, and the longer answer is that this effect is a function of the spectral content and becomes more-and-more prominent as the spectral content goes lower-and-lower in the audible frequency range.
This paper by acoustics expert, Paul Schomer, explains how noise at very low frequency levels can be heard. The fundamental issue is: Can we hear slowly surging or pulsating sounds for which the LEQ spectrum is below the threshold of hearing, where "slowly" means that the pulses come at a rate that is no faster than about 4 pulses per second? The short answer is yes, and the longer answer is that this effect is a function of the spectral content and becomes more-and-more prominent as the spectral content goes lower-and-lower in the audible frequency range.
If we now turn our attention to a wind turbine, the blade passage frequency is on the order of 1 second or less, and one of the newest machines, the Nordex N-100, a 2.5 MW wind turbine, has a blade passage frequency in the 0.5 to 0.7 Hz range. These pulses are not dissimilar to the 1 pulse per second scenario (above), so clearly pulses are and will be heard even if the LEQ is well below the threshold of hearing.
