A flat thin dynamic speaker which includes a motor unit, a suspension unit, a radiating unit and a frame arranged in such a manner that the motor unit and the suspension unit are at the same plane while the radiating unit is on top of the motor unit such that the thickness of the speaker assembly is reduced while the performance of the speaker assembly is maintained or even improved. Also, the speaker can be made into a quadrangular, polygon or a spherical structure. The speaker further has a surround at a level lower than the radiating unit without utilizing the radiating surface of the radiating unit such as a maximized radiating surface is provided, and includes a dual side voice-coil actuation to the radiator unit, thereby providing a slim and flat speaker assembly with high power output.