CT scans of violins can yield important data for research, give unparalleled arching and outline information to violin makers, and are surprisingly beautiful to see!
The Strad3D study violins were scanned as 600 'slices', which can be viewed as individual cross-sections, as frames in a video journey through the violins, or assembled into a 3d geometrical model of the entire violin, which can be rotated and studied from any angle.
CT videos shown here include several views including:
AXIAL (a series of sections taken across the width, showing internal and external arching)
WOOD (transparent 3D projection showing internal densities)
SURFACE (an opaque 3dD projection, showing a solid surface)
NB.Some strange visual "artifacts" are apparent in the CT images, a result of scanning interference from metal parts such as fine tuners and tail-gut adjusters.
The CT Arches and Outlines still images are 'slices' at familiar reference points, and show the coordination between the visible outer arch and channel, and the interior contours, with the concave curves of the channel reflected in the convex interior, which has a classic bell curve shape. The rib outlines give a direct view of the underlying designs, which have been examined and recreated using ancient design principals (See F.Denis; Two Forms, Strad3D).
CT scanning (Computed tomography) uses the same hospital equipment that is safely used on people. As with a patient, the violin passes through a special X-ray machine that creates a series of cross-sectional 'slices'. The differences in density are indicated by variations in the light and dark images, as in a conventional X-ray. The individual pixels of these 'slices' can be analyzed to calculate density, even comparing the relative densities of early and late growth spruce grain lines. (See B. Stoel & T. Borman; A Comparison of Wood Density between Classical Cremonese and Modern Violins, PLoS ONE.)
CT has proven invaluable to evaluate the condition and authenticity of collectable violins. (See Steve Sirr & John Waddle; Use of CT scanning for the detection of internal damage, repair and determination of authenticity in high quality violins, Strad3D)
As part of their Sirr and Waddle;s general research, they have calculated internal air volumes, and found that on most violins the soundpost position neatly bisects the internal air volume, an intriguing correspondence. In their database of Cremonese violin scans, the maple of the scroll has tended to be somewhat denser than the maple chosen for the back –a sensible choice for stability of the neck and resonance of the back.
Bissinger hopes to use the Strad3D data to create a digital 3D model, and add the vibration and damping data from the laser vibration scans to create a complex 'finite element' model, a computer-generated 'virtual Stradivari' in which individual variables such as arch height or wood properties can be changed at will, and the resulting vibration changes simulated and studied. Even a simplified finite-element model can dramatically show the effects of structural changes, as demonstrated by University of Birmingham physicist Colin Gough. This is a new frontier in acoustic research.