Ferromagnetic fluids are commonly used in speakers to absorb the heat generated between a voice coil and a magnet and it can passively weaken the cone movement. Ferromagnetic fluid is usually located in the air gap among the voice coil and is fixed by the magnet. Ferromagnetic fluid has the properties of para magnetism thus satisfying the law of Curie: when the temperature rises the magnetism decreases. Because of the heat generated by the magnet at work the ferromagnetic fluid magnetism is reduced and the eated ferromagnetic fluid flow is replaced by the cold ferromagnetic fluid on the periphery. This is an effective way of cooling off the outside world.