A stand-off device for use with acoustic transducers is described in which a chamber having a diaphragm portion contains liquid, the ratio of the acoustic impedance of said diaphragm to the acoustic impedance of soft body tissue and the ratio of the acoustic impedance of said liquid to the acoustic impedance of said diaphragm being whole numbers or fractions, and said diaphragm being of such thickness that reflections from its diaphragm/body interface, when it is held against the body of a patient, and its liquid/diaphragm interface tends to cancel each other.