The device (1) has a spherical oscillating drive head (3) for knocking on a metallic workpiece surface (2), and an actuator (4) for activation of the oscillating drive head for an oscillation with a knocking frequency. A resonance frequency of the device is variably adjusted to the knocking frequency of the device. The resonance frequency of the device is variably adjusted to the knocking frequency in a continuous manner within a modification range. The resonance frequency is varied depending of the knocking frequency in a stepped manner. The actuator is a piezoelectric actuator, a pneumatic actuator and an electro-dynamic actuator.