In this study, the experimental open-tube and close-tube thermoacoustic apparatuses were built. In order to determine the optimum length of resonant tube and the optimum length of stack, the resonant characteristics of thermoacoustic apparatuses were investigated, The length of resonant tube varies from 400mm to 850mm. The experimental frequency varies from 100Hz to 1000Hz. In case of the second and third harmonics, the maximum temperature difference of open-tube thermoacoustic apparatus is 53$^{circ}C$ (resonator length: 400mm) and the maximum temperature difference of closed-tube thermoacoustic apparatus is 51$^{circ}C$ (resonator length: 500mm). In the open-tube thermoacoustic apparatus, the peak efficiency point is about 2%, 55%, 69% in the resonant tube and in the closed-tube thermoacoustic apparatus, the peak efficiency point is about 2%, 41%, 50% in the resonant tube.