Pies, K: Bestimmung akustischer Kenngrößen an einem fahrzeug

While in the past the noise of the engine and other ancillary components of vehicles decreased, other components like the HVAC system have become more and more important. In upper class vehicles the aerodynamic noise of the air-conditioning system at high level might be annoying to the passengers. Modifications made at the late stage of the development phase are often very expensive. Therefore, it is more profitable to carry out tests and acoustic measurements related to both the whole HVAC system and single components at the early stage of the conception phase.This doctoral thesis presents the theoretical background of sound propagation in duct systems. Methods for determining the transfer matrices of HVAC elements, termination impedances, reflection coefficients and sound source characteristics are introduced. In addition to that, empirical approaches for calculating sound source characteristics of induct elements are presented.The experimental determination of acoustic characteristics is a main aim of this work. Therefore, different test benches are needed. An important aspect of these test benches is the examination of test objects independent of any vehicle. With this requirement test benches for the application of whole HVAC systems as well as several elements (e.g. ducts, bends etc.) were developed and validated.For a plane wave propagation the sound field in a duct system can be derived using transfer matrices. The value of these matrices of various sections and built-in components were determined by using a transfer matrix test bench.Another important parameter of HVAC systems is the termination impedance of air openings inside the vehicle. It is fundamental to describe the proportion of sound being emitted into the interior of a vehicle.Another test bench was developed, accounting for the necessary source characteristics and providing the following features: a defined air flow of "silent" air and sound excitation by using a noise source. The emission