Some further experiments with the beam diffraction model based on the uncertainty relation-is it valid also with double diffraction?

Motivation In room and city acoustics (noise immission prognosis), ray or beam tracing methods (RT/BT) are well approved. A version of RT is the statistical sound particle method with its detector technique [1]. BT is an efficient deterministic straight forward implementation of the mirror image source method MISM. The aim is still an efficient recursive introduction of diffraction, also for higher orders, but without explosion of the number of rays and computation time. Therefore the transition from RT to BT [2] and a convex subdivision [3] of the room seems necessary to allow an overlap of beams and hence a re-unification as it is proposed by the method of Quantized Pyramidal Beam Tracing (QPBT) [4]. The author ́s early energetic approach to diffraction based on the uncertainty relation (UR) [5] (to be published first time in-depth in 2010 in ACUSTICA [6]) has been improved in recent years in several steps [7], now utilizing BT, tested for many additional configurations. Reference cases were the semi-infinite screen and the slit (two edges) as a selfconsistency-test. At least Maekawa’s ‘classical’ ‘detourmodel’ [8] should be fulfilled. Later Svensson ́s exact wavetheoretical secondary edge source model [9] became the reference model. Last year, some discrepancies occurred, mainly with the non-fulfilment of the reciprocity principle in some cases. To overcome this, now some improved versions of the two basic functions have been tested: the ‘Diffraction angle probability density function’ (DAPDF) and the ‘Edge Diffraction Strength’(EDS). A new DAPDF could be derived from wave theory. Further more, the applicability of the model to double diffraction has been investigated numerically, a) at a slit, but now with finite source and receiver distances, b) at two edges in cascade, forming a ‘thick’ obstacle. This short paper is as a continuation of the last year’s paper [7] and only reports some results. Nevertheless, the basic features of the UR-based diffraction model shall be repeated.