A bellows for coupling a source of acoustic waves having an acoustic propagation medium, to a patient, has a geometrical modification in that region wherein the bellows can be seated against the patient for the introduction of acoustic waves into the patient. The geometrical modification in the propagation path of the acoustic waves generated by the source of acoustic waves shapes the acoustic waves in a designated (designed) manner. Additionally or alternatively, the bellows can have a section in the region that is formed of a different material than the rest of the bellows.