The Air Cavity

    One of the overlooked mechanics when examining the physics of insturments is the effects of the air cavity on the sound. Just as the strings, face plate, and back plate all have different modes which help to bring out individual tones, so does the air inside the guitar itself. It is from this cavity that the Helmhotlz resonance comes, as it is the lowest frequency resonance of the air inside the guitar and is mostly dependent upon the volume of air, and the shape and size of the sound hole (Fletcher 214). From this resonance other internal resonances are compared.

    Still, with a guitar it is hard to just separate each individual part to understand it. The Heisenberg principle could even be considered to apply when looking at the mechanics of this instrument. Each time you try to isolate a single part of the instrument to study itís principals, you change the system. If you look just at the resonance of the cavity inside the guitar, it means stopping resonance of the back and face plate, which in turn can change the volume of the cavity, affecting it just as it affects them. This holds true for all aspects of the guitar. When these aspects are taken into affect, there are usually three strong resonance frequencies formed from patterns of simple harmonic motion of the face and back plates.

This page last updated November 28, 1999.