A sound absorber usually consists of a perforated facing backed with a porous material, and is commonly used as a sound barrier, muffler in a vehicle or any other practical acoustic application. In this paper the normal incidence absorption coefficient determined only by the presence of rigid perforated screens is discussed. Various type of perforated screens with different percentage of perforations and backward with an air layer have been tested in an impedance tube experimental apparatus. Mathematical models for the determination of the superficial acoustical properties have been applied. Theoretical results and experimental data are compared. The paper particularly points out that the calculation of acoustical normal incidence absorption coefficient of the studied screens have a fairly good agreement with measurements at frequency below 2000 Hz.
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