Acoustic-parametric instabilities are a significant acceleration and self turbulization mechanism which may increase noticeably the propagation velocity of flames. Therefore, the acoustic-parametric instabilities for H-2-air mixtures at normal conditions have been investigated. The simplified analytical model proposed by Bychkov as well as the numerical solutions of the Searby and Rochwerger formulation were taken into account. The growth rate of the instabilities and the influence of different fuel concentrations and sound frequencies on the existence of spontaneous transition from the acoustic to the parametric instability were analyzed. The existence of a wavenumber range in which flames will be unstable for all intensities of sonic perturbations with adequate frequencies was postulated as a consequence of analytic investigation. This constitutes a significant flame acceleration mechanism with major impact on stability and flame development phenomena. (C) 2013 The Combustion Institute. Published by Elsevier Inc. All rights reserved.