An acoustic power transmitting unit for thermoacoustic systems includes at least one stage provided with at least two thermoacoustic units each of which includes a regenerator or a stack and two heat exchangers, an acoustic resonator including a tube and containing a fluid and in which a magnetic field having high impedance and low-impedance areas is arranged, wherein certain thermoacoustic units are placed in high dimensionless impedance areas. Each high dimensionless impedance area also includes a thermoacoustic unit, wherein two successive thermoacoustic units are always separated by low dimensionless impedance. The resonator includes a reduced diameter section between each couple of successive thermoacoustic units and each cross-sectional narrowing is associated with at least one by-pass which includes a deviation cavity and makes it possible to deviate the major part of a volume flow rate.