A program for predicting the sound power level from earth-moving equipment is under development in SHI. Fan noise is one of the major sources, whose contribution is greater than 40% of the total radiated noise power. The experiments show that both the blade passing frequency (BPF) component and the broadband component are important, and the directivity pattern is not symmetric with respect to the plane between the upstream and downstream flow. A noise source model of the fan radiator combination for predicting both the directivity and the frequency spectrum is developed from the experimental measurements. In this paper, a physical interpretation is made for modeling the types, shapes, and locations of the simple sources depending on the fan noise generating mechanisms. The minimum number of measurements for the cross-spectral approach are also considered based on the tolerable accuracy and the physically interpretable simplicity.