Maximum A-weighted Level Research Articles

Noise-induced annoyance from transportation noise: Short-term responses to a single noise source in a laboratory

An experimental study was performed to compare the annoyances from civil-aircraft noise, military-aircraft noise, railway noise, and road-traffic noise. Two-way within-subjects designs were applied in this research. Fifty-two subjects, who were naive listeners, were given various stimuli with varying levels through a headphone in an anechoic chamber. Regardless of the frequency weighting network, even under the same average energy level, civil-aircraft noise was the most annoying, followed by military-aircraft noise, railway noise, and road-traffic noise. In particular, penalties in the time-averaged, A-weighted sound level (TAL) of about 8, 5, and 5 dB, respectively, were found in the civil-aircraft, military-aircraft, and railway noises. The reason could be clarified through the high-frequency component and the variability in the level. When people were exposed to sounds with the same maximum A-weighted level, a railway bonus of about 3 dB was found. However, transportation noise has been evaluated by the time-averaged A-weighted level in most countries. Therefore, in the present situation, the railway bonus is not acceptable for railway vehicles with diesel-electric engines.

Effect of propagation distance on rotary wing aircraft sound duration

Military aircraft noise contouring programs employ an empirical factor describing the change in duration of a flyby with distance. In the past the SEL or EPNL was calculated from the maximum A-weighted level by the use of a duration correction given by 10 times the logarithm of the distance ratio, applicable to spherical divergence without absorption. Recent measurements have indicated that a better factor for a variety of military aircraft is six times the logarithm of the distance ratio (J. D. Speakman, “Effect of Propagation Distance on Aircraft Flyover Sound Duration,” AFAMRLTR-81-28, May 1981). This paper describes the results of an experimental and theoretical study of the duration factors for rotary wing aircraft. The theoretical study investigates the effect of surface conditions, coherence, and atmospheric absorption on the duration correction.