This work addresses the experimental investigation and analytical interpretation of a flame subject to acoustic-parametric instability exited by self-generated pressure pulses. The research presented herein was carried out with lean hydrogen-air mixtures during flame propagation in a smooth channel with an open end. It was found that very lean mixtures with hydrogen concentrations in air of less than 14% vol. H-2 generate acoustic oscillations due to flame instabilities, which, in turn, significantly influence the propagation of the flame. Above a 14% vol. H-2 concentration in the air, the flame becomes relatively stable with respect to self-generated acoustic perturbations. It was also found that an external polychromatic sound with a dominant frequency of 1000 Hz inhibits the instabilities and results in a reduced flame propagation velocity. Numerical solutions of the Searby and Rochwerger analytical formulation for the acoustic-parametric instability were utilized in order to analyze the experiments and study the influence of different parameters on the existence of a spontaneous transition from the acoustic to the parametric instability. (C) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.