Pioneering study of outdoor sound propagation (original) (raw)
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Experimental Outdoor Sound Propagation
2006
Noise propagation is significantly affected by prevailing meteorological conditions, leading to variations in received noise levels. Several standard modelling methods rely on measured meteorological data and estimation techniques. Rather than accept the uncertainty of modelling methods, we decided to obtain realistic and actual noise level data including the effect of atmospheric conditions by conducting a year long experiment on sound propagation. Loud speakers were placed at a central location on a site, to be used as an artificial sound source. A constant sound signal of a set of pure tones with varying sound intensity levels between each frequency is triggered every hour, for one minute, twenty four hours per day and for a year. The primary frequencies in the source signal were chosen to adequately simulate the main frequency range of typical mechanical plant. The transmitter consists of a CD player with a CD containing the source noise, a timer to trigger playback, a power amp...
Acta Acustica
The effective sound speed gradient is used to describe the meteorological conditions during sound measurements at roads and railways. Meteorological parameters were assessed up to a height of 10 m. The sound level differences between a reference point close to the passing vehicles and at distances of 100–500 m from motorways and railway tracks were determined. These differences were found to correlate well with the effective sound speed gradient determined from the measured temperature and wind speed gradients which follow the day/night cycle as a result of the reversing air temperature gradient, incoming solar radiation and wind conditions. The correlation with sound level differences can be approximated by an S-shaped function which is constant for large positive or negative gradients of the effective sound speed. These threshold values are a consequence of the local meteorological and attenuation conditions. The analysis shows that large effective sound speed gradients are mainly...