This paper shows and discusses the use of the finite element software ANSYS for simulation of the behavior of sound waves in a ducts-plenum system. The modeling is intended for didactic purposes, beginning with simple three-dimensional geometries of ducts and plenum. Two conditions can be included: (1) with and without acoustical absorbent materials on the inside walls of the ducts and (2) including or not labyrinths. The analysis allows students to see the behavior of the waves inside the duct-plenum system and they can manipulate the parameters of the model to improve the attenuation characteristics of the system.