To investigate the characteristics of the sound-pipe on the top of King Song-Dok bell, using computer simulation, the throat impedance was evaluated for the straight pipe and conical pipes with varying taper angles. When sound propagates in a rigid walled, unflanged circular pipe with wavelength larger than radius, the acoustic motion is planar, much as in a bar. The incident sound waves are reflected at the end of pipe and some of them are transmitted. The reflection coefficient and radiation impedance of the sound-pipe of King Song-Dok bell were calculated, and the results demonstrated that the high frequency sound is radiated through the sound-pipe. It behaves like a frequency filter.