saif bunni's portfolio, blog and research.

Bowl Acoustics

I can feel air whooshing past my ears as I stand above the bowl. The movement at the bowl rim is so powerful it causes such a cool breeze. If you concentrate enough, you can probably hear this in the videos.

For the first time in history, here are several modes of vibration of a bowl actually and physically demonstrated, filmed and documented. About a year ago, I started researching into resonant frequencies, and was obsessed with finding the resonant frequency of every object I hold. Bowls are a great design to work with. Bowls tend to exhibit very prominent resonant frequencies, bowls of all kinds. Glass ones from the kitchen to composite metal ones used in Tibetan singing bowls.

So in order to test objects for their ‘resonance’, eventually I started winding my own coils (which work in the same principle as the ones used in a dynamic speaker’s voice coil). The Water Speaker as well as the bowl are powered by the same design of coil.

It is probably false to use the term ‘resonant’ or ‘resonance’ frequency at all. This term misleads one to think there is only one frequency the object will resonate at. The fact is there are multiple frequencies and possibly an infinite amount the object can vibrate in sympathy with. This is commonly referred to as Modes of Vibration. Obviously we are only able to hear within our human hearing range (roughly 27Hz – 17000Hz).

I’ve read few papers about Bowl Acoustics, some of them include A. P. French’s Wineglass Acoustics (which can applied to a bowl as well) and more recently Denis Terwagney and John W.M. Bushz Tibetan Singing Bowls in 2011. Most theorise this phenomenon, but none demonstrate or document it in real life. As with anything, theory can only go so far as when the experiment is actually done, many other ‘quirky’ phenomenon appear. Aside from Wineglasses, this can applied to many other bowl shaped objects.

I’ll be possibly be releasing this in more of a ‘paper’ format i.e. as a downloadable PDF Document. This will be a more thorough insight into this phenomenon along with theories, detailed photographs and illustrations. I am not a scientist though. I am just a curious Art student, so you don’t have to believe me. Apart from the hard facts, some of what’s written here are just very likely speculations.

In summary, the Youtube Playlist above documents few of the modes of vibration of a custom-made (using the metal spinning process) Aluminium Bowl of thickness 0.9mm and diameter 280mm. The modes will be numbered according to how many nodes shaped around the bowl’s rim [as seen in the video] i.e. 4th Mode is ~41Hz, 6th Mode is ~117Hz and 8th Mode is ~227Hz. Naming it this way can be confusing, as for example the 4th Mode could be actually the first one that is physically possible. Odd number of wavelengths are impossible as symmetry governs the shape of the bowl and similarly all objects in existence.

Currently almost jobless, and lacking in tools, you can support the development and progress of this research by donating few quid through buying some of my piano albums! I am currently in desperate need for a high speed capture camera, as you can see the videos are fairly poor quality. If this have been filmed before, please let me know. I look forward to get in touch with others who are working on this, or collaborations from visual artists, researchers, and creators.

You’ve seen this first here.
© Saif Bunni 2014