Beamforming in modalen Schallfeldern von Fahrzeuginnenräumen

  • Beamforming in modal sound fields of vehicle interior

Nau, Clemens; Vorländer, Michael (Thesis advisor); Jax, Peter Johannes (Thesis advisor)

Berlin : Logos Verlag (2016, 2017)
Book, Dissertation / PhD Thesis

In: Aachener Beiträge zur technischen Akustik 25
Page(s)/Article-Nr.: IV, 169 Seiten : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2016

Abstract

Physically the conventional beamforming method (CBF) is based on a decomposition of the incident wave field into plane or spherical elementary waves whose relative phases are interpreted to mean that the directions of incidence and source locations can be identified and classified. A central assumption of the CBF is its application in the acoustic free field. This assumption is particularly invalid in confined spaces such as a vehicle interior, in which to a certain frequency range (below the Schroeder frequency) modal influences dominate the sound field. Under these conditions the CBF only shows a poor localization ability; up to a complete localization failure. However, to apply beamforming under these conditions and in this frequency range, in this thesis two approaches are being pursued in parallel to minimize the room acoustic influences on the Beamforming and thus improve the localization result particularly in a vehicle interior. A first approach is based on the pre-processing of cross-spectral matrix (CSM) using the so-called generalized cross-correlation. A second approach uses "macro modeling" to approximate the pole frequencies of the room transfer functions. Based on the determined pole frequencies an inverse filter is automatically generated, which also applied to the CSM minimizes modal influences before the actual beamforming. Both approaches are as well discussed theoretically as practically examined and evaluated in consecutive steps. For this purpose, based on principle studies on defined reflection surfaces, the behavior of both approaches inside a scale model room are shown, analyzed and evaluated. Subsequently, both approaches are evaluated under the real conditions of the vehicle interior. A digression regarding the combination of beamforming with arbitrary transfer functions for the further development of the beamforming beyond the free field assumption concludes the investigation work. Finally, this thesis is concluded by the chapter "Zusammenfassung und Ausblick".

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