An irregular-shaped plate with dimensions identical to a guitar soundboard is chosen for this study. It is well known that the classical guitar soundboard is a major contributor to acoustic radiation at high frequencies when compared to the bridge and sound hole. This paper focuses on using an analytical model to compute the sound power of an unbraced irregular-shaped plate of variable thickness up to frequencies of 5 kHz. The analytical model is an equivalent thin rectangular plate of variable thickness. Sound power of an irregular-shaped plate of variable thickness and with dimensions of an unbraced Torres’ soundboard is determined from computer analysis using ANSYS. The number of acoustic elements used in ANSYS for accurate simulation is six elements per wavelength. Here we show that the analytical model can be used to compute sound power of an unbraced irregular-shaped plate of variable thickness.