A simple method based on plane‐wave normal incidence is used to calculate the transmission coefficient, reflection coefficient, and absorption coefficient of a wall structure. The performance of the wall structure for enclosing the noise source is estimated by a term called “noise reduction,” which is the ratio of the sound intensity at the exterior side of the wall to the sound intensity at the same point with no enclosure present. Several structures with combinations of impervious layers, air space, and sound‐absorbing material are evaluated and used as examples to demonstrate the effect of mass, acoustical impedance, propagation constant, and arrangement of materials (impervious layer, absorbing material, and air) on the acoustical performance of the wall.