a therapy apparatus for treatment with focused acoustic waves which has a source of focused acoustic waves , an acoustic receiver for the reception of parts of the acoustic waves reflected from a subject to be acoustically irradiated , and can be switched from a therapy mode to a locating mode . the apparatus also include circuitry for varying the oscillatory frequency of the generated acoustic waves dependent on whether the apparatus is switched to the therapy or locating mode . a method for operating such an apparatus is also disclosed .