If you hold Tibetan Singing Bowls in your palm, it stays free to vibrate. Then, you can softly rub a mallet across the edge of it. This is what causes the singing noise, often used for Tibetan meditation. You can also softly bump the wall of the bowl. This generates a bell-like noise. Either way you play crystal singing bowls, it is the vibrations that create the sound, like if you glide your finger around the edge of a champagne glass. The pitch of the noise can be altered depending on the bowl width. Bowls can range in diameter from 4 to 15 inches. You can also increase the mallet spin rate to alter the sound.