Sound Propagation in Urban Areas

Abstract

Outdoor sound communication systems for urban areas have been traditionally designed using relatively few sources of sound, located high above the buildings. Results have generally not been satisfactory because of sound attenuation in the atmosphere and diffraction by buildings. As an alternative, a block by-block coverage system using many sound sources placed in the streets has been investigated. Extensive acoustical and meteorological field tests carried out in city streets showed that sound-propagation conditions are generally favorable there. Typically, the mean wind and temperature gradients are small; consequently, no appreciable sound refraction effects were observed over distances of a city block or two when sound was propagated from a source 10–20 ft above the pavement. Reverberation from the building walls was not detrimental to speech intelligibility when a directive sound source was used with its axis oriented along the street. However, the intelligibility of speech received in a side street some distance away from the intersection was poor owing to excessive sound attenuation and reverberation.