Sound image method and sound energy vortex in rectangular room

Sound particle velocity is irrotational and achve sound intensity may sometimes be rotational. With the development of the measurement of sound intensity and the active noise control, the interest of studying the rotational characteristics of sound intensity and the sound energy vortex has been increasing. In this paper, we discussed the sound image method for rectangular room with light-absorption walls, derived a method for computation of number of sound images and their positions, and gave equations for sound field variables. As an example, we computed sound pressures and the phases of sound pressure waves on a cross-section of a room, and drew diagrams to show sound energy streamlines on the cross-section. The diagrams show that some energy streamlines roll up to form energy vortexes. Around vortex point is a rotational sound wave. The dimensions of vortexes are dependent on sound frequency and decrease with the increase of frequency. It can be predicted that the vortexes would disappear at higher frequencies.