Violin vibration state determined from laser streak patterns

One of the main objectives of violin acoustics is a detailed analysis of the vibration state of the instrument, the source of its sound. The goal of this work was to extend a straightforward technique, naked-eye and non-destructive, to detect details of violin vibrations: laser streak patterns. Essentially, the experimental set-up only requires harmonically driving a violin in resonance, illuminating its surface with a handheld laser, and focusing on the speckle plane. The streak patterns obtained from signature modes of the violin revealed details hardly available using other real-time techniques. For example, results showed the behavior of the island —the area between the f-holes— changing from rigid rocking in CBR to bending motion in B₁^- and B₁⁺; in fact, the high sensitivity of the streak patterns even allowed detecting specific areas with major deflections on the island: the soundpost side in B₁^-, and the bassbar side in B₁⁺. Therefore, employing streak patterns as a tool for real-time analysis of violins is encouraged not only for researchers but also for violin makers.