ABSTRACT
Acoustical phenomena in a closed room are the main focal problems in architectural acoustics. In this chapter fundamental theories are described and their practical applications are discussed.
3.1 SOUND FIELD IN A ROOM
A. Characteristics of the Indoor Sound Field While the characteristics of the outdoor sound field are rather simple because the sound wave from the source spreads out freely, assuming there is no obstacle, then attenuates with distance, the sound emitted
indoors creates a very complicated sound field due to multiple reflections from walls, ceiling and floor. The characteristics of the indoor sound field are as follows. (1) The sound intensity at a receiving point remote from the source is not attenuated as much as in free space even if the distance is large. (2) Reverberation occurs due to the reflected sound arriving after the source has stopped. These two features are quite distinct from the outdoor situation and are very important. Moreover, depending upon the room shape and surface finish, peculiar phenomena like echos, flutter echos, etc, which result in a complicated acoustic field are observed. This is mainly due to the effect of surrounding walls which determine the room shape. Therefore, the purpose of the study of room acoustics is to control the above described phenomena by means of room boundary conditions such as room shape and finishing materials and to create a satisfactory acoustical environment in the space.
