Abstract: The experiment of measuring sound velocity in university plays the important role in comprehending the knowledge of wave superposition and standing wave. However, the sub-maximum phenomenon existing in the resonance interference method usually results in mistakes during experiment.This paper discusses quantitatively this phenomenon.Based on the numerical simulation of Matlab software, Fourier spectrum analysis of the information pro- duced by signal generator,and compared with the experiment data, the conclusion is that the sub-maximum phe- nomenon is not related with the sub-frequency signal.

Key words: ultrasonic, standing wave, sound velocity measurement, sub-maximum, quantity