Finite-amplitude stationary acoustic waves in a closed resonator subjected to simultaneous excitation at fundamental frequency and its second harmonic are analyzed in the frame of the second-order nonlinear theory. The conditions when the dual-frequency excitation leads to a quality factorQhigher than in the case of a single-frequency excitation are derived. TheQenhancement can be explained in terms of active suppression of cascade processes of the generation of higher harmonics. The second harmonic generated in the resonator is compensated by the second harmonic radiated by the piston. Suppression of higher harmonics also can be explained as being due to effective down conversion of energy from the second harmonic to the fundamental wave in the nonlinear parametric process.