Physics of the guitar at the Helmholtz and first top-plate resonances
Ian M. Firth · The Journal of the Acoustical Society of America · 1977
The action of the guitar has been studied in detail in the vicinity of the Helmholtz air resonance and the first resonance of the top plate. Measurements of the input mechanical admittance, the output sound pressure, and their phases suggest an analogous acoustical circuit for the guitar identical with that used to describe the action of a loudspeaker in a bass-reflex enclosure. Below the Helmholtz resonance sound radiated from the rose and from the top plate are out of phase. As a result sound radiated from the guitar is not enhanced by the rose. Above this resonance sound output from the rose and top plate are more nearly in phase with a resulting enhancement of radiated sound.