Can wind turbine sound that is below the threshold of hearing be heard?

Abstract

This paper is geared towards wind turbine sound, but it is really a simple variation on the basic concepts that this author used in the development of loudness-level-weighted sound exposure (Schomer et al., J. Acoust. Soc. Am, 110(5), Pt. 1, 2390-2397, 2001) and of Rating Noise Curves (RNC) (Schomer, Noise Cont. Eng. J., 48(3), 85-96, 2000), which are used in the Standard, ANSI/ASA S 12.2 Criteria for evaluating room noise. 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. So surging or pulsing sound that is primarily in the 16 or 31 Hz octave bands will show the greatest effect. This paper shows the applicability of these results to wind-turbine sound. © 2013 Acoustical Society of America.