Sensation and Measurement of Low and Very Low Frequency Time-Varying Sounds in Accordance with the Very Short Impulse Response of Low-Frequency Human Hearing 2011-01-1665

Human hearing, with its active transducers, attention process and remarkable signal-processing abilities, challenges the transportation-product sound quality engineer to measure accordingly and has clearly given rise to the practice and tools of sound quality engineering. Transient events and/or level changes of various durations and magnitudes and over various frequency bandwidths are measurable with due care in the majority of “real-world” acoustic time-signal histories, and frequently carry subjective importance. Inspired by recent work with wind-turbine sound situations, the focus of this paper is to suggest reconsideration of some low-frequency measurement methodologies in the transportation realm. Results will be presented coherent with the hearing system's unusually short impulse response at low and very low frequencies (principal magnitude within about 10 milliseconds, slight effect to about 75 milliseconds), which make low-frequency impressions not only sensitive to time variation, but even to very short-term transitory levels. Hearing-event evaluation is strongly weighted by short-term near-peak values not revealed in overall results and largely erased in conventional constant-percentage-bandwidth measures versus time such as 1/3-octaves. This sound quality concept is generally known and applied at mid and high frequencies, but would be productive to extend to low and very low-frequency sensation and measurement.