In order to build more powerful sources of sound for energy conversion, the synchronization of two thermoacoustic heat engines has been studied. Experiments were performed on engines in the acoustic frequency range of 2.6 kHz and also on very small engines in the ultrasonic range of 24 kHz. In both cases, the engines were mounted on a cylindrical cavity, and they were coupled mainly by the acoustic field in the surrounding air at one atmosphere. They were driven by heaters of resistance wire in contact with the hot heat exchanger. At a specific coupling between the 2.6 kHz, engines' synchronization occurred, and also for the 24 kHz devices; frequency pulling in each pair of engines led to a common frequency in each set, i.e., in-phase synchronization. The strength of the synchronization was determined as a function of detuning of engines. Mutual entrainment was observed at the onset of oscillations and this is attributed to drive by fluctuations. Moreover, as a result of synchronization, the critical temperature gradient for onset of oscillations was reduced from that of the individual values. Delays between two oscillators in the start up led to quenching of the generated sound output ( oscillation “death” of Rayleigh).