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Based on the experience that the acoustic characteristic variables Γan, Zan of fibrous absorber materials can be expressed by one nondimensional variable E=fρ0/Ξ with sufficient accuracy for survey calculations, the sound absorption of absorber layers has been calculated and plotted in a way that permits at the same time the reconstruction of the frequency curve of sound absorption for individual absorbers, as well as quantitative answers on questions of general interest, which up to now have been discussed in literature mostly in qualitative manner only. The sound field was assumed to consist of plane waves, with either normal, oblique, or diffuse incidence. The absorber layers could be either locally reacting or bulk reacting. The same holds for air cavities that could exist between the absorber layer and the rigid wall. A general recurrence calculus for computation of the input impedance or the reflection factor and absorption of multilayer arrangements was presented. Some numerical examples of its application were shown, in conclusion.
F.P. Mechel (Tue,) studied this question.