ABSTRACT
Sound propagation outdoors is governed by completely different physical phenomena to sound propagation in rooms. However, in both cases, there is a direct sound field propagating away from the sound source. In a room, the sound field is reflected from room surfaces to generate a reverberant field in addition to the direct field. In addition, for rooms with lightweight walls such as aircraft, there will be coupling between the acoustic field in the room and the dynamics of the enclosing walls. Outdoors, no reverberant field is generated, but the direct sound propagation is influenced by the ground, the atmosphere and any obstacles in its path. This chapter provides an overview of how sound pressure levels may be estimated at significant distances from outdoor sound sources and also at some distance from a sound source in a room. For a more thorough treatment of outdoor sound propagation, the reader is referred to Chapter 5 of Bies and Hansen (2003) and a more detailed treatment of room acoustics may be found in Chapter 7 of the same book.
