From transmitting frequency responses in water, admittance measurements in air and water, and radiation patterns in water, calculations were made of the electro‐acoustic efficiencies at 1250 kc of four one‐inch squareX‐cut quartz crystals of practically equal thickness having radii of curvature of ∞, 25, 7, and 4 centimeters, respectively. Efficiency values calculated from acoustic measurements do not check as well with the calculated potential efficiencies as do those calculated from admittance measurements. The latter values indicate that the radiation resistance the same for the four crystals. Focusing measurements show agreement with A. O. Williams' prediction that the point of maximum acoustic intensity in the radiation pattern is not necessarily at the center of curvature of the crystal. Resonance frequencies obtained from admittance measurements in air make plausible the deduction that the effective mass of a crystal decreases with increasing curvature.