Ernst Chladni: Physicist, Musician and Musical Instrument Maker

Acoustical work

Chladni is best known for his work in acoustics, and for his invention of a method for visualizing the patterns of vibrations on mechanical surfaces. The Whipple has two examples of 'Chladni plates' - metal plates that can be caused to vibrate using a violin bow. Building on pioneering work done by Robert Hooke (1635-1703) in Oxford during the late 17th century, Chladni revealed the patterns of vibration using fine sand, which settles into the nodal lines (areas of zero displacement) producing striking and beautiful shapes. Chladni's demonstrations attracted the interest of the French Emperor, and amateur scientist, Napoleon Bonaparte (1769-1821) who was so impressed that he financed the translation of Chladni's major work Die Akustic into French, which appeared in 1809 (image 2).

Chladni also conducted some of the first research into tuning forks, paving the way for the perfection of these implements as musical and scientific instruments. This study was the technical groundwork for his best known musical instrument, the clavicylinder. This keyboard instrument worked using resonating metal bars, like tuning forks, which were pressed against a rotating felt-covered friction wheel. Chladni spent many years touring Europe giving performances of popular works by famous composers. The instrument enjoyed widespread acclaim, but unfortunately for Chladni it never caught on as a serious orchestral instrument, being outshone by Benjamin Franklin's (1706-1790) glass armonica.

How they work

The Whipple's plates are made of iron and are caused to vibrate by stroking with a violin bow. When stroked, a given plate will resonate at one of its natural frequencies. The experimenter then sprinkles fine sand, which bounces about on the plate until settling at nodal points (areas of zero movement) thereby producing intricate patterns such as the one shown in image 3. This technique of visualisation was invented by Chladni and documented in his book Die Akustic (published 1802).

Theoretically, any plate has indefinitely many possible vibration modes each corresponding to a specific frequency of sound. Each mode produces a unique pattern, the complexity of which increases with the frequency of the vibration. The shape of the patterns produced on a given plate depends on other factors, including the shape of the plate itself. One can get a sense of the variety of possible patterns from the accompanying illustration from Chladni's book (image 4).