An experimental study is presented on the characterization of the noise transmission properties of the duct junctions of ventilation and air-conditioning air circuits, assumed as three port acoustic systems. The procedure requires the measurement and post-processing of the transfer functions between the control signals of 3 loudspeakers, one at each branch, and the sound pressure signal recorded at 6 positions (two microphone technique). This paper describes the basis of the methodology and presents some of the results obtained for branch take-offs with three deviation angles and under different air flow conditions.
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