Uneven, Local Absorber Surface

This section uses the method described in the previous → Sect.  D.7 . The “unevenness” may be modelled either with a variation of the normalised absorber admittance G(x,y) or with a variation of the co-ordinates of the surface. The first method can be applied to grooves and narrow valleys, for example; the second method is applicable for slow or random variations.

If the absorber surface can be represented by a reference plane with a variable admittance $G(x,y)$, then the admittance first is described by its Fourier series. The following example assumes in A a one-dimensional variation of the admittance $F_{{0}}$ of the surrounding baffle wall in the form of a cosine modulation with the period length $\ell$, and the average admittance over the absorber side length a in the x direction of a rectangular absorber with with the function \(\begin{array}[]{l@{\,}c@{\,}lr}G(x)&=&F_{0}+B\cdot\cos(2\pi x/\ell)~~~~~~~~~~~~~~~~~~~~~~~~~&(1)\\ &&&\\ &&&\\ \langle G\rangle&=&F_{0}+B\cdot...