The above image depicts a Tibetan singing bowl with a mallet which has one of its ends covered with wool. Now take the mallet in your hand and hit the bowl at its upper side with the end having wool of the mallet. Eventually, you will hear a specific sound from the bowl. Now place the woolen end of mallet on the upper surface of bowl and move it around the circumference of the upper plane of the bowl. To see this all in action watch this video
You will notice that as you move the mallet, the sound made becomes louder and louder. Explain this phenomenon.