How Himalayan singing bowl produces 'chatter' decoded

Complex 'stick-slip' motions of the wooden stick used to play the Himalayan singing bowl is responsible for the "chatter" or rapid knocking sounds that the Tibetan instrument emits, researchers have found.
A Himalayan singing bowl operates much in the same way as a wine glass - slide your fingertip, or a wooden stick called a puja, around its rim to hear its soothing tones.
The bowls, which originated in the Tibetan mountain region and are made of metal alloys, have been used for meditation and worship since around 500 BC, but have found recently new audiences in contemporary music.
While the complex stick-slip motions responsible for "chatter," or rapid knocking sounds, have been extensively studied in other instruments, few have studied this action in the Himalayan singing bowl.

Researchers from Rollins College in US have studied the motion of the Himalayan singing bowl and found the origin of "chatter," which occurs when the puja is played against the bowl.
"As the puja moves around the rim of the bowl, it switches very quickly between sticking to and slipping on the metal, which is called 'stick-slip motion,'" said Chloe L Keefer, an undergraduate at Rollins College.

This motion is responsible for producing sounds in a wide variety of musical instruments, including the violin and cello, and many additional non-instrument vibrational processes.
Using a laser Doppler vibrometre, a scientific instrument for making non-contact measurements of the vibrations of a surface, researchers measured vibrations at several points on the inner rim of the bowl near where the puja contacted the bowl.

"The puja's motion excites the vibration of the singing bowl, causing a unique deflection shape," Keefer said.
Their experiments showed that the puja forces a point of zero vibration called "a node" on the bowl, which lies in the vicinity of the contact point of the puja.
"The interesting part of the puja's motion is that people would expect the puja to lie on the node of the bowl's vibratory motion, but in fact it doesn't," Keefer said.
Rather, this node lies within two millimetres of the puja, she said.
As the puja rotates around the rim, the node follows behind it, and as the puja rotates faster and faster, the displacement or the vibration amplitude of the rim increases accordingly.

When the amplitude of the vibration is large enough, it will briefly knock the puja off the bowl, producing chatter.