Modal Analysis – Overview
As seen with Spectral Analysis, every violin has a unique assortment of resonance peaks, at many different frequencies (pitch), and with varying amplitudes (loudness). Any instrument will have a unique set of vibration Modes (patterns of motion) associated with each of its frequency peaks. In real use an instrument vibrates in many different ways simultaneously, to create the mix of frequencies that comprise any note.
Modal Analysis breaks down this complex mix of motions, frequency by frequency, to create maps and video animations of mode behavior. These new imaging tools are so vivid that a violinmaker or musician can begin to absorb this vision in an intuitive way. The smallest modifications to these modes may be audible in the sound. And as seen in the 3D Modal Movie, the hidden motions of the violin are also extraordinarily beautiful. The movements in these animations are of course very exaggerated and slowed to be easily tracked, but do represent the real motion of the violins. (See Common Questions about Modal Animation, Strad3D)
Why were 3d vibration studies used rather than the more usual 2dstudies? 2dstudies do show the 'out-of-plane' pumping motions that produce most sound. 3d studies also show the 'in-plane' motions less effective for sound, but which can lead to effective out-of-plane motions when the vibrational waves reach an edge (plate-rib join) or a discontinuity (f-holes, bass bar) and thus add to the sound output.
Signature Mode Shapes: (Stoppani) is a text and animation slide show, which gives an introduction to the basic modes. In addition to showing the areas of maximum surface displacement, some of these animations track areas of maximum bending, indicated by color variations.
The Modal Video Viewer has two sections:
Air and corpus animations:(Bissinger) these show not only the signature mode body vibrations, but also the movements of air pumping in and out of the f-holes, which is so critical to lower frequency sound radiation.
Band Averaged movies: (Stoppani) a way to quickly study a large amount of data. Included are comparisons of a Stradivari, Guarneri violins, and Bergonzi violin, and contrasts of mobility vs. bending.
The 3D modal Animation Files (WINDOWS only) can be directly viewed and manipulated; Install the Polytec SCANVIEWER, and modal files found in Get Files
For further reading, see See Bissinger research papers, and Modes and More (Stoppani, a basic introduction) all found in Research and Articles.