Outdoor sound propagation over ground with several impedance discontinuities

Abstract

Extensive studies have been made on the outdoor propagation of sound over a surface of finite impedance as well as over a surface with an impedance discontinuity. Under realistic field conditions, the ground surface over which sound is propagating has several discontinuities. This paper deals with the propagation of sound from a well‐defined sound source over a surface characterized by a finite number of infinitely long parallel regions of ground with homogeneous impedance within each region, but the impedance varies from one region to another. The sound source itself generates one tone at considerably higher levels than the higher order harmonics. The analytical results are presented in comparison to experimental measurements obtained from testing conducted under actual field conditions. Factors such as topography and meteorology, which would otherwise contribute to the excessive attenuation, have been omitted in order to isolate the effects of a finite number of impedance discontinuities. Because the analytical study has been validated by field results the findings will improve prediction methods of environmental noise from sources of discrete tones (e.g., high power transformers, I.D. and F.D. fans, etc.) propagating over realistic outdoor ground conditions.