FEM simulations and experimental validation of frequency response prediction for acoustic soundboards

In this paper FEM models of several acoustic soundboard were produced. Initially a simplified case of a rectangular plate similar to a distributed mode loudspeaker was simulated, followed by an acoustic guitar soundboard with fixed constraints at the edges. A process of model fitting was performed, in the attempt to match the orthotropic behaviour of the material used for the membranes, namely red cedar.

Thanks to this step-by-step approach, both the Eigen-modes analysis and the forced response were computed in order to predict the overall frequency spectrum of the acoustic guitar soundboard. Eventually, an informative comparison between simulated data and measurements was obtained.

Results indicate that FEM modelling and a measurement system could become vital manufacturing tools to optimise the workflow in the luthier shop when a specifically tailored response needs achieving. Data also shows that even a simplified FEM model exploiting wood’s specific anisotropic properties can be accurate and helpful when designing new bracing patterns or analysing specific instrument’s resonances.

Future research will expand the presented FEM simulations to include the guitar’s body with its Helmholtz resonator, and the mutual coupling of the sides and the backplate. This will increase the accuracy of the available predictions and will possibly capture more similarities between acoustic instruments and loudspeaker enclosures.