If you grasp Tibetan Singing Bowls in your grip, it is free to vibrate. Then, you can gently rub a mallet across the edge of it. This is what causes the singing sensation, often used for Tibetan meditation. You can also quietly tap the wall of the bowl. This makes a bell-like sound. Either way you play crystal singing bowls, it is the vibrations that generate the sound, like if you glide your finger around the edge of a champagne glass. The pitch of the singing can vary depending on the bowl density. Bowls can range in diameter from six to twelve inches. You can also increase the mallet velocity to modify the sound.