Porous metallic material and its compound sound absorbing structures are very popular for the practical applications in harsh environment such as high temperature, humidity, and high sound pressure levels. There are all kinds of mathematic models available to predict the sound absorption properties of porous metal in literatures elsewhere. In this work, Cellular Automata is applied to model the acoustic filed in an impedance tube with and without porous metal. In this Cellular Automata model, a center difference scheme to discretize the linear wave motion equation is used to deduce the local interaction rules between the cells on the different boundary and their neighbor cells. In particular, the local interaction rules between the cells on the given acoustic impedance boundary and other neighbor cells have been improved to predict well the sound absorption and propagation inside impedance tube at lower frequencies. After the improvement, the complete standing wave shape at lower frequencies inside impedance can be observed clearly. Also the propagation of the forward and backward travelling waves including the resultant standing wave with regard to time and space has been depicted relatively completely. Finally, the analytical result for the sound absorption properties of porous metals in impedance was put forward for comparison. And a good agreement between the results related to the different approaches was obtained as well.
