Thermoacoustic Effect allows conversions between mechanical energy and thermal energy by using sound waves (aka "pressure waves"） as medium. The process starts with the gas being heated in the "hot region", a treatment that inflates gas volume. The inflation then results in the gas being pushed into the region of lower temperature, the “cool region,” and this relocation shrinks gas volume as previously acquired heat is losing. Simultaneously, inflated gas creates sound waves that spread outwards at the speed of sound, causing wave reflections in certain mechanic structures such as tubes and chambers. Consequently, gas that was losing heat during the preceding mechanism returns to the hot region, where the gas is re-inflated. This process of gas inflation and re-inflation altogether forms a cyclical heat-sound self-excitation, thus the name of "thermo (heat) acoustics (sound)".
Thermoacoustic applications can be done both in forward ("positive") processes or backward("negative") processes. During forward processes, thermal mechanisms lead to the creations of sound waves, which could be transformed into mechanical energy. Thermoacoustic engine, a new form of heat engine, works based on such forward processes. The backward processes work in exactly the opposite way. In certain mechanic structures, sound waves produced by other equipment lead to the "pump-heating" phenomena. The pump-heating effect allows manipulation of temperature by acoustic impacts on gas volume. Through fine acoustic designs, backward thermoacoustic processes can be used to produce cryocoolers and heat pumps.