Modeling the low-frequency response of an acoustic guitar

Abstract

The low-frequency response of an acoustic guitar is strongly influenced by the combined behavior of the air cavity and the top plate. The sound hole–air cavity resonance (often referred to as the Helmholtz resonance) interacts with the first elastic mode of the top plate creating a coupled oscillator with two resonance frequencies that are shifted away from the frequencies of the two original, uncoupled oscillators. This effect was modeled using finite elements for the top plate and boundary elements for the air cavity with rigid sides and back and no strings. The natural frequencies of the individual and combined oscillators were then predicted and compared to measurements. The model predicts the mode shapes, natural frequencies, and damping well thus validating the modeling procedure. The effect of changing the cavity volume was then simulated to predict the behavior for a deeper air cavity.