The short answer
A singing bowl produces more than one frequency when it vibrates. Its spectrum contains a lower modal component and additional higher-frequency partials that contribute brightness, complexity and beating. These higher components are commonly called overtones, although they are not necessarily exact integer “harmonics”. Their strength and decay help give each handmade bowl its individual character.
Acoustics / physics
Partial, overtone, harmonic
Acoustics / physics
A partial is any single frequency component of a complex sound, including the lowest. An overtone is any partial above the fundamental. A harmonic is the stricter case where a partial falls at a whole-number multiple of the fundamental. Strings and air columns produce near-harmonic series. Bowls generally do not, so “partial” is the accurate word and “harmonic” is usually the wrong one.
Why a bowl behaves this way
Acoustics / physics
A bowl is a shell, not a string. Its modes are two-dimensional patterns of deformation around and up the wall, and their frequencies are set by radius, height, thickness, curvature, stiffness and density together. Nothing in that geometry forces the modes into integer ratios, so the resulting spectrum is inharmonic — which is exactly why a bowl sounds like a bowl rather than like a plucked string.
Where beating comes from
Acoustics / physics
A perfectly symmetrical shell would have modes that occur in pairs at identical frequencies. Real hand-formed bowls are not perfectly symmetrical, so those pairs split slightly. Two components a fraction of a hertz apart produce a slow pulsing in loudness. That pulsing is one of the most recognisable characteristics of a handmade bowl, and it is a direct audible consequence of the forming process.
Excitation decides what you hear
Acoustics / physics
The same bowl presents differently depending on how it is excited. A tap deposits energy across many modes at once, so the initial sound is complex and the upper partials are prominent before they decay. Rim rubbing feeds energy continuously through a stick–slip friction interaction and preferentially builds one mode, which is why rim playing sounds purer and more sustained than striking.
How ANURAVA records this
Rather than publishing a single number, the measurement method stores the operational fundamental and the strongest persistent partials above it, each with a frequency and a relative amplitude. They are recorded as dominant partials, not harmonics, because the word has to stay accurate even when the marketing would prefer otherwise.
Frequently asked
Why does my bowl have several tones?
Because it vibrates in several modes at once. Each mode radiates its own frequency, and you hear the combination as one complex sound with shimmer and movement in it.
What is an overtone in a singing bowl?
Any frequency component above the fundamental. Overtones give a bowl its brightness and complexity, and their relative strength and decay are a large part of what makes one bowl sound different from another.
Are singing-bowl overtones harmonics?
Usually not. Harmonic means an exact whole-number multiple of the fundamental. Bowl partials are generally inharmonic, so ‘overtone’ or ‘partial’ is correct and ‘harmonic’ is normally inaccurate.
Sources & methodology
- Peer-reviewed acousticsTerwagne & Bush, ‘Tibetan singing bowls’Nonlinearity / MITModels bowl vibration from radius, height, wall thickness, stiffness and density; tapping excites multiple modes, rubbing preferentially excites one.
- Peer-reviewed acousticsAcoustical Society of America literature on Himalayan singing bowlsJournal of the Acoustical Society of AmericaStick–slip rim excitation; self-excited modes depend substantially on contact friction and the material of the rubbing implement.
- First-partyANURAVA Acoustic Method v1.0 and Sound Passport recordsANURAVAFirst-party measurement protocol and per-instrument documentation.
Written and reviewed by ANURAVA. Where a statement rests on a musical convention or a traditional association rather than on measurement, it is labelled as such in the text above.