Nowadays, the noise quality in the interior of a car is mainly influenced by the noise emitted by the HVAC system. 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 important. The HVAC system itself includes the fan, the whole duct system with internal fittings and the air vent. In addition to the fan, which is regarded as a primary sound source, flow induced noise also occurs at valves, bends and air openings, and thus it also has to be taken into consideration for the description of the entire noise characteristics. The sound transmission from the source to the outlet is determined by the transfer characteristics of the flow ducts and components. If the sound propagation is mainly one-dimensional, the acoustic transfer matrix model can be applied to simulate the transmission characteristics. However, it is not possible to take partial sound sources of transmission elements into account. This paper aims at implementing a sound source approach into the transfer matrix description of duct systems. The transfer matrices of various sections and built-in components were determined by using a transfer matrix test bench. 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 characteristic values obtained during these measurements can be implemented into the calculation model in relation to parameters, such as flow rate or position of the valves. The paper concludes with a comparison of the results obtained by calculations and by various measurements. The results presented in this paper show that calculating the sound propagation in ducts can be realised by using the transfer matrix method. The advantages are that reflected waves are included and the sound field is calculated and given for every point in the whole duct system. It is even possible to implement sound sources within the duct system. To validate this method, all parameters, such as reflection coefficients, transfer matrices, sound source characteristics, were measured.
Implementation of a sound source approach into the transfer matrix description of duct systems
2009
9 Seiten, 8 Bilder, 9 Quellen
Aufsatz (Konferenz)
Englisch
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