Sound is not normally produced by striking but by rotating a mallet (shaped like a pestle) in a circular motion around the inner upright edge of the bowl (again - the easiest way to imagine this is as the movement of a pestle within a mortar). Such instruments are not normally "struck". A famous misconception is perpetuated by the scenes at the beginning of the Rank film where a man is seen striking a huge gong full on with a mallet. In fact, most percussionists will tell you that the way to get the best sound out of gongs is in fact to rotate the mallet around the surface of the gong in a circular motion. This allows the vibrations of the gong to trigger initial sounds which cause secondary vibrations and sounds, such that the noise keeps building, almost in a self-perpetuating way.

Regarding the sounds and pitch, instruments of this kind are not normally "pitched" as we would understand it in the western musical tradition. The design of most gongs allows the intrinsic properties of the metal they are made of to create not one sound, but many. The larger of the two is pitched approximately at F sharp, the smaller at A (a minor third above F sharp). The registers of these notes are approximately in the octave above middle C on the piano. The A and the F sharp are the most obvious sound among the tones the bowls produce; there is a strong hint of a second frequency approximately a fifth below the two notes referred to.

This article is not the place for a detailed explanation of the acoustic properties of gongs and bells, which are interesting but esoteric. Suffice it to say that were the sounds generated by the bowls to be passed through modern sampling and recording systems, you would see quite clearly that they produce a great many sounds, some of which are beyond the normal spectrum of human audibility. Sizes of singing bowls range approximately from 7" to 13" in diameter, and in rarer cases sometimes larger. The smaller the bowl, the higher the pitch. The unusual quality of the sound is derived both from the shape of the bowl, as well as the special alloy from which it is made. The pitch of the bowl depends upon its thickness, size and weight.

Another facet to take into consideration is that the modern tonic sol-fa which we use in the west is inappropriate in the context of Oriental music which typically tends to use different scales and modes, some including half and quarter tones. Thus to speak of the bowls' pitch in western terms is misleading. (They are normally categorised as unpitched percussion in western musicology).These instruments would not probably have been designed to pitch at any note in particular that has any meaning in a western context, however it is possible that the pitches are significant in their own musical context since the frequency of the vibrations was said to tune into corresponding areas of the human body.

Sound creates powerful vibrations - we all know that music can strongly affect moods, but it goes much deeper than that. Research in physics shows that different body parts resonate to different tones. In health, the tones are balanced, but when one part of the body is sick, its frequency is off, sending the whole system off balance. The bowls are thought to resonate with various parts of the body such that they are said to clear chakras and enable healing. One possible explanation for this is that the alloy from which the bowls are made is composed of seven sacred metals, corresponding to the sacred seven planets: gold (Sun), silver (moon), mercury (Mercury), copper (Venus), iron (Mars), tin (Jupiter), antimony (Saturn), and beyond to the chakras.

Tibetan traditions feature the use of sound as one of the paths to enlightment. This is referred to as Nada Yoga. It is a healing path. However, the uncontrolled use of sound frequencies can be highly damaging to people and buildings. There are many modern examples of buildings and ear-drums damaged by constant vibration and noise. Joshua was said to have bought down the walls of Jericho using a trumpet! So it is not surprising that there are accounts which state that it is forbidden, even within the monasteries, to talk about the bowls and that the highest lamas used them in secret rituals to travel to other dimensions and other realms. The legends say further that the secrets of sound yield so much power that they must be kept hidden. The deep, insistent, resonating sound of the Tibetan trumpet (not dissimilar to an Alpenhorn), even second-hand as a music recording, has quite a peculiar physical effect upon the body. (Interestingly, other Tibetan wind instruments are commonly made out of leg bones!)

 It is probably more accurate to think of the bowls as being Buddhist in origin, rather than Tibetan. From approximately 500 B.C., the time of the Buddha Shakyamuni, the harmonics of singing bowls have been used to induce meditation and assist spiritual seekers to the state of enlightenment. Previously used in Tibet for meditation and ceremonial purposes, legend holds that mantras recited during the making of a Tibetan Singing Bowl are absorbed into the metal and released when the bowl is played, vibrating with resonant tones.

The singing bowl may have originated as a Buddhist offering bowl, sometimes containing barley, flower or rice, water, and/or butter with a wick placed in the center to create a butter lamp. Though the unique design of the bowls, particularly the emphasis on the thick rim, indicates an emphasis on their acoustic properties rather than on their capacity to hold food. Interestingly, these bowls are not used for their tonal qualities in Tibetan Buddhist rituals although they are often struck to signal the end of meditation sessions. The bowls may often found in sets of 4; in the Buddhist tradition, one for each element (Air, Fire, Earth and Water).

Sadly, production of the genuine singing bowls in Tibet, ceased when it was invaded by China, though there are still Tibetan exiles living in northern India who manufacture the bowls according to the traditional method of layering the various metals of the alloy.

There are many websites where singing bowls may be purchased online (see below). These sites are also rich in information, some of which was used as the basis for this article.

Sources:

www.bodhisattva.com
www.tibetanspirit.com
www.himalayanbowls.com
www.tibetanimports.com
www.paulawalla.com
www.singingbowl.com
www.frankperry.co.uk