Answer: It stops the sound because the sound works with pressure and an outrageous from it's volume
Explanation:
A cymbal is known as a musical equipment which is heated at the surface or it's opening to form a sound. The working principle for it's performance is based on it's volume or the shape of the vessel, pressure applied and how it's been applied. Placing your hand at the mouth opening stops the noise because of you're being able to control the volume with application of pressure.
Vibration is the pleasant and unpleasant wavering of an equipment to form a motion.
