Diffuse Sound Reflection at a Bulk Reacting Porous Layer

The integral for $\alpha _{{dif}}$ from → Sect.  D.5 of bulk reacting absorbers generally must be evaluated numerically. The diagram below shows a contour plot of $\alpha _{{dif}}$ for a porous layer of thickness d with hard back over the non-dimensional parameters $F=f\cdot d/c_{{0}}$ and $R=\Xi\cdot d/Z_{{0}}$. In the parameter range above and on the left-hand side of the dash-dotted curve, the absorption coefficients of a locally reacting and a bulk reacting porous layer agree with each other. In the range above and on the right-hand side of the dashed straight line, the bulk reacting layer effectively has an infinite thickness.