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What's Different About the Sound of Singing Bowls?

(See also "The Healing Powers of the Glass Armonica")

A glass armonica (also known as the glass harmonica) is basically a set of tuned glass (or quartz) singing bowls. What makes the musical sound from wine glasses and glass/quartz bowls different from that of other instruments? (The difference described here would also apply to Tibetan singing bowls, which are made of metal instead of glass.)

A string, like a guitar string, is an example of a something that can only vibrate at a set of "musical" frequencies, which is why we hear it as a musical sound — one that has a definite pitch (such as "middle-C").

When you pluck a guitar string, you're putting energy into the system, and for a very brief period of time it vibrates at a huge range of non-musical frequencies (the initial unpitched "pluck" sound). But in just a few thousandth's of a second the string all but ceases to vibrate at the non-musical frequencies, leaving only the musical ones.

When you pluck a guitar string, you're actually creating "waves" in the string, like waves on a lake. One of these waves might look like this:

(The size of the wave is grossly exaggerated for purposes of illustration.) When the wave reaches the end, it's reflected back the way it came:

When it reaches the other end, it's reflected again, repeating the process.

The string in this example is called a "wave guide", because it "guides the wave." In the case of a vibrating string, the wave guide is basically a straight line, so it's a "linear wave guide".

Wind and brass instruments are also "linear wave guides", but instead of "a string being stretched", it's "air being compressed". Apart from that, wind and brass instruments (like flutes and trumpets) work in essentially the same way as vibrating strings.

A wine glass is also something that can only vibrate at a set of "musical" frequencies. But there's a difference: instead of being a linear wave guide, it's circular. Instead of the wave guide being a line, it's a circle. Looking down on the top of a wine glass:

The wave actually goes around and around the rim in a circle. (There is also a corresponding wave going in the opposite direction.) This makes it a circular wave guide1. But because a circle has no end, the wave is never reflected. In essence a circular wave guide is infinite in the same way that a circle is infinite.

Examples of linear wave guide instruments:

  • Piano, guitar, and all string instruments
  • Woodwind instruments
  • Brass instruments

Examples of circular wave guide instruments:

  • Glass armonica (glass harmonica) — associated with healing
  • Wine glasses
  • Tibetan singing bowls — used for meditation
  • Singing bolws in general are associated with healing and used for meditation
  • Bells — associated with the spiritual realm practically the world over
"The Healing Powers of the Glass Armonica"
1See Serafin, S, Wilerson, C, Smith III, J.O, Modeling Bowl Resonators Using Circular Waveguide Networks, Proc. of the 5th Int. Conference on Digital Audio Effects (DAFx-02), Hamburg, Germany, Sept. 26-28, 2002