We have constructed a simple loop-type thermoacoustic engine and measured the pressure change at the 13 points along the loop tube with three kinds of the stack shape. The profile of the pressure amplitude along the loop was analyzed assuming the generating wave is piling up a pure progress and standing wave. The results show that the pressure amplitude both a progress and standing wave depend on mesh size of the stack material and the temperature gradient at the stack. The generated progress wave progress wave propagates from both side of the stack to the loop-tube and the ratio of the pressure amplitude depends on the operational conditions and stack shape.
