A thermoacoustic transducer apparatus comprising: a mechanical converter operable to provide power conversion between acoustic power and mechanical power, the mechanical converter including at least one diaphragm defining a compression chamber and an expansion chamber within the mechanical converter, the at least one diaphragm having a diaphragm surface area; a thermal converter including a flow passage having a regenerator portion thermally coupled to provide power conversion between acoustic power and thermal power, the regenerator portion having a regenerator flow area; the mechanical converter being in fluid communication with the flow passage of the thermal converter through transmission ducts (110,112) extending between the compression chamber and the flow passage and between the expansion chamber and the flow passage respectively, the transmission ducts completing an acoustic power loop through the flow passage between the compression chamber and the expansion chamber, the acoustic power loop having a working volume for containing a working gas and being operable to facilitate acoustic power flow between the compression chamber and the expansion chamber, and characterized in that: a cross-sectional area of the transmission ducts is less than the regenerator flow area and the regenerator flow area is less than the diaphragm surface area; and the at least one diaphragm is operable to undergo resilient displacement to cause pressure oscillations within the working volume and wherein the acoustic power loop is configured to cause at least one location along the acoustic power loop to have pressure oscillations that have an anti-phase relation to pressure oscillations in the mechanical converter. a mechanical converter operable to provide power conversion between acoustic power and mechanical power, the mechanical converter including at least one diaphragm defining a compression chamber and an expansion chamber within the mechanical converter, the at least one diaphragm having a diaphragm surface area; a thermal converter including a flow passage having a regenerator portion thermally coupled to provide power conversion between acoustic power and thermal power, the regenerator portion having a regenerator flow area; the mechanical converter being in fluid communication with the flow passage of the thermal converter through transmission ducts (110,112) extending between the compression chamber and the flow passage and between the expansion chamber and the flow passage respectively, the transmission ducts completing an acoustic power loop through the flow passage between the compression chamber and the expansion chamber, the acoustic power loop having a working volume for containing a working gas and being operable to facilitate acoustic power flow between the compression chamber and the expansion chamber, and characterized in that: a cross-sectional area of the transmission ducts is less than the regenerator flow area and the regenerator flow area is less than the diaphragm surface area; and the at least one diaphragm is operable to undergo resilient displacement to cause pressure oscillations within the working volume and wherein the acoustic power loop is configured to cause at least one location along the acoustic power loop to have pressure oscillations that have an anti-phase relation to pressure oscillations in the mechanical converter. a cross-sectional area of the transmission ducts is less than the regenerator flow area and the regenerator flow area is less than the diaphragm surface area; and the at least one diaphragm is operable to undergo resilient displacement to cause pressure oscillations within the working volume and wherein the acoustic power loop is configured to cause at least one location along the acoustic power loop to have pressure oscillations that have an anti-phase relation to pressure oscillations in the mechanical converter.