PURPOSE: To provide a thin and small sensible acoustic device with good excitation efficiency and vibration propagation efficiency and its vibration unit which can be fitted to the space, etc., formed in the crossing position of the sitting part and the back part of the seat of an automobile.

CONSTITUTION: A cross section U-shaped vibration propagation frame 1 fitted with a voice coil 2, a plate damper 8 positioned so as to be horizontal to the voice coil 2 and constituted of a slender flat plate fitted separately from the both tip parts of the vibration propagation frame 1, and a yoke 7 fitted to the central part of the plate damper 8 are equipped, and the vibration is constituted to be obtained by the magnetic interference effect that occurs between the magnetic force to be generated from the voice coil 2 accompanying the audio signal of the bass area and the magnetic force of a magnetic pole 6.