Chladni plates: the first step towards visualizing sound

Chladni plates, invented by the physicist, musician and musical instrument maker Ernst Chladni XR  (1756-1827) in the late 18th century, are used to demonstrate the complex patterns of standing wave G  vibrations that can occur in two-dimensional objects. The Whipple's collection contains two examples from King's college London, made and used in the laboratory of the physicist Sir Charles Wheatstone XR  (1802-1875).

Chladni plates and accessories
Image 1 Collection of Chladni apparatus built and used in King's College London, late 19th century. Image shows two Chladni plates, a double bass bow and illustration of Chladni patterns. Image © the Whipple Museum (Wh.3446).
Chladni pattern on plate
Image 2 Dr Rees demonstrates the production of a pattern on a Chladni plate using a violin bow. Image © the Whipple Museum (Wh.3446).
Illustration of Chladni patterns
Image 3 Illustration of Chladni patterns from Chladni's Die Akustic (1802). Image © the Whipple Library.
Jim Woodhouse demonstrating Chladni patterns
Image 4 Professor Jim Woodhouse demonstrating the use of Chladni patterns to examine violin body resonances. Image © the Whipple Museum.

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 2. 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 G  each corresponding to a specific frequency G  of sound. Each mode produces a unique pattern, the complexity of which increases with the frequency G  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 3).

Musical use

Chladni plates have been used for serious research and are instructive as learning tools, but modern researchers are interested in the vibrational behaviour of more than just sheets of iron. Stringed musical instruments like the violin and the guitar rely on the resonance G  of their wooden bodies to amplify and colour the sounds produced by their vibrating strings. Chaldni's methods can be applied to violin and guitar bodies and used by instrument builders to 'tune' the resonances G  of the instrument. Image 4 shows professor Jim Woodhouse of the Cambridge University Engineering Department demonstrating Chladni patterns on a violin back plate.

» Read more about Ernst Chladni

» Read about Charles Wheatstone and his symphonium

Torben Rees

Torben Rees, 'Chladni plates: the first step towards visualizing sound', Explore Whipple Collections, Whipple Museum of the History of Science, University of Cambridge, 2009 [http://www.hps.cam.ac.uk/whipple/explore/acoustics/ernstchladni/chladniplates/, accessed 24 July 2016]

 
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