high-frequency techniques and random matrix arguments, both for classical waves such as vibroacoustics [@TS07; @WW10], electromagnetics [@GG14; @Gro14] and for quantum mechanics [@GMW98; @Sto99; @Haa01; @Meh04]. Spectral and wave function statistics are universal under very general conditions and, in particular, if the system under consideration is complex with an associated ray dynamics being chaotic [@BGS84]. The statistical properties depend then only on a few generic parameters such as the mean level density, the mean wave amplitude and underlying symmetries such as time-reversal symmetry. Deviations from universality may occur due to non-chaotic dynamical features and for many wave systems in practical engineering applications, these deviations are of great practical importance. In addition, the spatial dependence of mean field values is itself of interest, particularly if absorption or other dissipative effects become relevant.

Classical wave problems – such as the vibro-acoustic response of complex built-up structures or the electromagnetic wave field inside a complex cavity – have in common that they are typically driven by complex, that is, spatially extended but finite, stochastic, and broad-band sources. In addition, they are typically dissipative and are often composed both of regular components (rectangular rooms, walls or corridors, for example) and irregular components (such as 