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Published on Feb 12, 2014
"It was after placing the isolated mechanism of a clockwork 'musical box' directly onto the sounding box of a guitar that I first noticed deep vibratory tones that could not have been directly generated by the high-pitched lamellae vibrating the air. These were subtones caused by the vibration of the mechanism against the hard surface, but in varying patterns of division. The patterns were aided by feedback from the resonating body back to the mechanism, and vice-versa, so that the high frequencies of the musical box tones were being divided by the patterned way in which the weight of the mechanism made on-and-off contact with the surface."
I found the same effect could be produced with a vibrating tuning fork gently pressed against newspaper, where it naturally makes contact at various audible modes of vibration.'
Previously regarded as only a theoretical inversion of the overtone series, this short video* presentation explains how the 'undertone series' (or sub-harmonic spectrum) can actually be generated spontaneously using a tuning-fork and a piece of paper. It is also possible to produce undertones on violin instruments through a skillful bowing technique.
*This is an HD re-upload of the videos originally published in December 2010, later replaced in May 2012.