We present results of numeric and experimental study of mechanical vibrations of an upper sounding board of a classical guitar. We employ a set of rods and plates that are finite elements for modeling a sounding board. Considering frequencies up to 550 Hz, we obtain frequency-response curves. We consider also the influence of supporting elements that are asymmetrically spaced reinforcing rib (springs) on the dynamic properties of a sounding board. It is established that a set of resonance amplitudes of a guitar sounding board with supporting elements is of good quality compared to a sounding board with no ribs. Natural frequencies obtained from calculations are in good agreement with experimental data.