Pattern formation in parametric sound generation
  Pattern formation of sound is predicted in a driven resonator where subharmonic generation takes place. A model allowing for diffraction of the fields (large-aspect ratio limit) is derived by means of the multiple scale expansions technique. An analysis of the solutions and its stability against space-dependent perturbations is performed in detail considering the distinctive peculiarities of the acoustical system. Numerical integration confirm the analytical predictions, and shows the possibility of patterns in the form of stripes and squares. 
Isabel Perez-Arjona and Victor J. Sanchez-Morcillo