A two-dimensional model for control of centrifugal fan inlet noise in a notebook computer

Abstract

Previous work on active control of exhaust noise from small centrifugal fans demonstrated significant reductions of the blade passage frequency (BPF) tone. A fan and heat-sink were placed within a mock-up notebook computer case, and control of the fan exhaust noise was measured. It was found that control of the BPF in the exhaust did not significantly affect noise radiated from the fan inlets into the notebook casing, suggesting that exhaust noise and inlet noise may be controlled separately without one adversely affecting the other. In the current work, a two dimensional half-space, source coupling model has been developed to calculate the field within the notebook casing caused by the inlet noise. As a first approximation, free-space boundary conditions were used. A two-dimensional space was constructed to test the model, and error sensor placement was predicted. Measurements of radiated sound power show significant reduction of the blade passage frequency tone. Factors influencing experimental agreement with the model are discussed, such as modal effects and primary source location.