Above the critical power input of the phase transition, the thermoacoustic oscillation is ignited in channels filled with He II at the atmospheric pressure. The clear sound is continuously generated under some conditions of the channel configuration. The characteristic frequency of the thermoacoustic oscillation, which depends on the channel length, is complementarily discriminated by means of a microphone and an oscillatory disk. Except for the thin layer of the triple phase transition near the heated surface, the temperature distribution along the channel length is held during the thermoacoustic oscillation.
