ABSTRACT
The wave propagation in gaseous and liquid media can be described by the three variables: the pressure p, the particle velocity u, and the density p. The relation between these is described by the wave equation, and this can be derived from three basic equations: the Euler equation, the Continuity equation, and the State equation. The diffuse field is obtained in a reverberation room where all walls have been made, in principle, 100% reflective. At the same time, the walls are made nonparallel and the result is a sound field with sound waves in all directions. The closed coupler is a small chamber, with dimensions small compared to the wavelength of the sound. A special case of this is the standing wave tube. This is a tube with a diameter smaller than the wavelength and with a sound source in one end.
