ABSTRACT
In particular, sound absorbers are usually employed to meet one of the following objectives: This chapter discusses the principles and mechanisms of the most important types of sound absorbers. Even if the walls, the ceiling and the floor of a room were completely rigid and smooth, they would cause some sound absorption which, however, is quite small. The sound absorption caused by audience is mainly due to people's clothing and its porosity. There are two ways to determine experimentally the sound absorption of audience and seats. In particular, sound absorbers are usually employed to meet one of the following objectives: To adapt the reverberation of the room, for instance, a performance hall, to the intended use of it. To suppress undesired sound reflections from remote walls which might be heard as echoes. And to reduce the acoustical energy density and hence the sound pressure level in noisy rooms such as factories, large bureaus and so on.
