Human ears cannot hear the sound waves produced by the ultrasonic parts cleaner because they are outside the normal audible frequency range. But they have ultrasonic power to get things really clean. When these ultrasonic waves are irradiated into the cleaning liquid, cavitation continuously occurs in the liquid and a high pressure of 1,000 atmospherics is created to clean whatever it touches. There is also the cleaning effect of the cleaning liquid agitation, removal of bubbles and emulsification so that without causing any scratches even microscopic dirt is taken away.