Aircraft noise characteristics and metrics
Abstract
Day-Night Average A-weighted Sound Pressure Level (DNL or Ldn) is used currently to define noise contours around airports and the 65 DNL contour is used as a criterion to determine qualification for noise insulation programs. There is concern that this metric based on average A-weighted sound pressure with penalties for noise occurring at night does not adequately account for annoyance or broader noise impacts such as sleep disturbance. Much more sophisticated measures of perceived sound level (loudness) that adjust frequency weighting based on the characteristics of the sounds exist. Although loudness is considered to be the strongest noise attribute contributing to annoyance, there are other sound attributes, such as sharpness, tonalness, roughness and fluctuation strength that can also influence annoyance. In this research, several studies were conducted to examine effects of noise characteristics on annoyance ratings of aircraft noise. A simulation program was developed to simulate aircraft noises so that individual characteristics could be varied while keeping others constant. Investigations on the influence of single characteristics such as spectral balance, roughness, fluctuation strength, and tonalness on annoyance ratings of aircraft noise have been conducted. Some evidence of an increase in annoyance with increases in roughness and tonalness was observed in these investigations. The influence of tonalness and roughness on annoyance ratings in the presence of loudness variations was also observed. Even when both loudness and tonalness varied, a strong sensitivity to tonalness persisted. Tonalness was the dominant sensation when both tonalness and roughness was varied and loudness was kept constant. The importance of tonalness and roughness increased when loudness did not vary very much. It was found that loudness, tonalness and roughness were, respectively, the first, second and third most influential characteristics. It was also seen that the use of Loudness exceeded 5% of the time (N5) rather than Equivalent A-weighted Sound Pressure Level (LAeq) produces better predictions of average annoyance ratings. None of the metrics or models that are currently used for environmental noise annoyance incorporate measures of loudness, tonalness, and roughness together. In this research, a model based on the Psychoacoustic Annoyance developed by Zwicker, Fastl and other that combines the effects of loudness, tonalness and roughness to predict annoyance due to aircraft noise was developed. The developed model was found to be a better predictor of aircraft noise annoyance than any other metrics or models that are currently used to evaluate aircraft noise.
Degree
Ph.D.
Advisors
Davies, Purdue University.
Subject Area
Mechanical engineering
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