PREDICTION AND MEASUREMENT OF THE ACOUSTICAL IMPEDANCE AND ABSORPTION-COEFFICIENT AT OBLIQUE-INCIDENCE OF POROUS LAYERS WITH PERFORATED FACINGS

Sound absorbers consisting of a perforated facing backed with a porous material have been used in architectural acoustics for many years. This paper describes a method to calculate the surface impedance and absorption coefficient at normal and oblique incidences. Two types of construction, with and without air space, are studied. Comparisons are made between theoretical predictions and measurements performed in an anechoic room with the two-microphone technique.