Microphone Array Applications in Cabins

Air transportation has always been linked with aeroacoustic noise generation. To study these noise generating effects wind tunnels are used with scaled models because of the limited wind tunnel size. But studies of interior noise problems with scaled models are difficult as the model structure behaves differently in terms of sound transmission compared with an authentic cabin. Therefore, an in-situ measurement technique for source localization during operation is needed. In addition to the other noise-generating sources the aerodynamic and aeroacoustic excitation of the fuselage causes energy transmission into the cabin. The sound field generation is induced by structure-borne sound radiation of the lining (or window or floor). Due to the limited space in cabins and a vibrating lining which surrounds the measurement area, a pivotable array with 60 microphones was constructed. Because of the reverberation in cabins, sound source localization with conventional beamforming is not possible, so that an average beamforming method has to be used for sound source localization. A comparison between average and the conventional beamforming methods will be shown. First results from measurements in the DLR Do728 cabin test facility will demonstrate the source localization in cabins with this method. The average beamforming method is not limited to aircraft cabins and can be used for sound source localization in high-speed trains as well