The Body

The body: the front and back plates, the sides and the air inside - all serve to transmit the vibration of the bridge into vibration of the air around the instrument. For this, the violin needs a relatively large surface area so that it can push a reasonable amount of air backwards and forwards. The most important part is the belly. The belly or top plate. The belly and back plates are made so that they can easily vibrate up and down. The plates have a number of resonances: ie there are certain frequencies at which they vibrate most easily. These are identified by luthiers and scientists using Chladni patterns. To make the graph at right, isolated bellies were driven mechanically at the position of the bass foot of the bridge, and the acceleration was measured. The graph gives the ratio for force to acceleration. If we were vibrating a small mass m, the ratio would be that mass, independent of frequency. However, the resonant behaviour of the plate appears here: the acceleration produced by a given force is a strong function of frequency. On this graph, each major resonance is indicated by an inset photograph of its Chladni pattern. The two curves here are for the bellies of two rather similar violins. When the violin is assembled, the resonances are more complicated. However, the resonances are very important in transmitting the varying force exerted at the foot of the bridge into radiated sound.

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