Double‐dumbbell transducer elements of two commercial nickel‐copper‐cobalt‐ferrous ferrites (Ferroxcube 7A1 and 7A2) with acoustic “pressure‐release” material at each end were placed between the jaws of a hydraulic pressure testing machine. The effective electromechanical coupling coefficient for the sample was measured for various magnetizing currents and static loads. As the load was increased to 5600 lb, corresponding to 4600 psi in the narrow “limbs” of the element, the effective coupling coefficient at optimum bias decreased from 0.21 to 0.05, and the clamped inductance (which is proportional to the incremental permeability) decreased by 40 per cent.