The invention concerns a reactor with acoustic cavitation comprising a tube (10) made of flexible material, wherein the liquid to be treated circulates. Electro-acoustic transducers (1) are radially and uniformly distributed around the tube (10). Each electro-acoustic transducer (1) has a general prismatic shape with a base of specific width and a head narrower than the base, the head pressed on the tube (10). Each electro-acoustic transducer (1) includes an electro-acoustic motor (78) mounted at the base such that the vibrations generated by the electro-acoustic motor (78) are amplified at the head by the electro-acoustic transducer (1) shape. Lubricating films (9) extend between the electro-acoustic transducers (1) heads and the tube (10), so as to produce an acoustic coupling of the electro-acoustic transducers with the tube. The whole set is in a sealed chamber (83) where the pressure is maintained at a predetermined value and where the lubricating and cooling liquid circulates.