Decoded: How Himalayan singing bowl produces 'chatter'

Have you ever wondered how a Himalayan singing bowl produces soothing tones much in the same way as a wine glass does? A team of young US researchers has revealed the 'how' of those rapid knocking sounds or "chatter".

The bowls, which originated in the Tibetan mountain region and are made of metal alloys, have been used for meditation and worship for three millennia since around 500 BCE, but have found new audiences only recently in contemporary music.

While the complex stick-slip motions responsible for "chatter" have been extensively studied in other instruments, few studies have investigated this action in the Himalayan singing bowl.

Recently, a group of under-graduate researchers from Rollins College, Florida, revealed the origin of "chatter" which occurs when the wooden stick called 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, one of the researchers.

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 vibrometer -- a scientific instrument for making non-contact measurements of the vibrations of a surface - Keefer's team 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 explained.

The 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 added.

Rather, this node lies within two millimeters of the puja, she explained.

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.

In addition to instruments, the research that the team performed can also advance an understanding of brake squeal in automobiles.

The study was presented at the meeting of the Acoustical Society of America (ASA) in Jacksonville, Florida, this week.