This paper is devoted to phenomena related to convergent beam propagation in a medium with concave areas on the slowness surface. Experiments have been performed on crystalline silicon plate of (001) orientation with a convergent probe beam of an impulse acoustic microscope. The probe signal penetrates from immersion into crystalline specimen as convergent beams of longitudinal and transverse waves that reflects from the plate bottom and are recorded as a sequence of echo pulses – B (from the face) and L, LT and T impulses ( from the bottom, produced by diverse types of waves propagating through the plate).