A shock wave adapter for use with a focused shock wave applicator has a flexible, rigid or semi-rigid membrane or housing adapted to be filled with a fluid. The membrane or housing is devoid of any air or gases and when filled forms a spacer volume for passing acoustic shock waves at low impedance. The wave pattern of the shock wave applicator enters the membrane or housing as a converging wave form to a focus inside the membrane or housing and exits through the membrane or housing in a diverging wave form into the patient to be treated. The spacer adapter may further include a gas filled shield around the perimeter of the fluid filled membrane or housing to block transmissions of acoustic shock waves.