Frequency Response Evaluation of Acoustic Guitar Modifications

This paper investigates the effect of various modifications to an acoustic steel string guitar on lowfrequency dynamics and sound pressure level. Modifications include string tension, sound-hole area and depth, bridge pin mass, top plate mass, stiffness and damping. Frequency response measurements are provided for all modifications considered. A lumped parameter model is found to capture the changes in measured frequency response and sound pressure level remarkably well. The measurements and model results are found to be consistent with player and listener perceptions in most cases. Results from a parametric study identify a unique combination of physical parameter adjustments for broadband increase in sound level. In addition, a technique for obtaining low-frequency free-field sound pressure without the need for an anechoic chamber is successfully applied to the acoustic guitar. This technique uses near-field, time-selective impulse response sound pressure measurements to determine the low-frequency free-field sound pressure.