Making Matters: Something in the air

New Figure 2

Steve Sirr and John R. Waddle use CT scans to examine the internal air volume of 20 Cremonese violins, and make a surprising discovery about the soundpost position

Since we performed the first CT scan of a violin in 1987, the non-invasive procedure has become standard practice in the study of bowed stringed instruments. In our previous articles we have used CT scans to examine various instrument properties such as the wood density, mass and volume. Others have written about the possible design of the parts of the instruments, including geometric and proportional systems. Now we turn our attention to air.

One could say that a violin has no measurable air volume, as the f-holes form openings in the top. However, if we ignore that for study purposes and pretend that there are no f-holes, we can find a value for the interior air volume. This is done by making CT ‘slices’ showing an instrument’s lateral cross-section, each of which has a thickness of 0.5mm (figure 1). We then calculate the area of each slice, subtracting everything but the air: the front and black plates, ribs, blocks, linings, soundpost, bass-bar and any repair work. We then multiply the remainder by the slice thickness to find the internal air volume of each slice in cubic centimetres…

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