Onset and damping temperatures are important characteristics for thermoacoustic engine which decide the level of low grade thermal energy that can be utilized. Using loudspeaker to drive thermoacoustic engine is an effective method to decrease the onset temperature. In this paper, the onset process of forced oscillation driven by loudspeaker was investigated comparing with that of self-excited oscillation. Impacts of driving frequency and power on onset temperature were discussed. The results show that forced oscillation has a higher selectivity for driving frequency. The self-excited oscillation frequency (fundamental frequency) is the optimal choice to drive thermoacoustic engine in practical application. The lowest onset temperature was gradually achieved with the increase of driving power. Pressure amplitude is mainly affected by the onset temperature. The lower the onset temperature is, the smaller the pressure amplitude is. This work provides a guide for the selection of driving signal in practical application. (C) 2012 Elsevier Ltd. All rights reserved.