Active Noise Control in a Semi-Closed Aircraft Cabin

Abstract

An active noise control system is developed for the loadmaster area of a propeller driven transport aircraft. The loadmaster area is a small semi-enclosed volume connected to the large cargo hold. This coupling of a small room with a large room yields to new questions when an active noise control system is designed: Which effects does the coupling have on the noise field inside the small loadmaster area? Which influence do these effects have on the active noise control system? How complex is the uncertainty induced by the coupling to the large cargo? The analysis of this coupling was done in two ways. The first one, an energy based method, is used to analyze the acoustical energy flow between the loadmaster area and the cargo hold. The second one, a substructure technique, is used to study the influence on the eigenfrequencies and eigenmodes of such a coupled system. Afterwards, the theoretic results were confirmed with an experimental forced vibration analysis. The most important result is that the shape of the noise field inside the loadmaster area is less sensitive in spite of the large cargo hold. Moreover, an active noise controller was developed to handle the controller tasks. First experimental control results are given in the last section. These results have shown successful noise reduction up to 23 dB without any controller optimization.