"Cross Flow Fan" sound wave propagation in the medium, medium energy will continue to be absorbed and converted into other forms of energy, which is caused by absorption of acoustic attenuation. In the medium absorbs sound waves caused by attenuation of the high frequency noise attenuation faster than the low-frequency noise, because the high-frequency acoustic vibrations fast, medium consumption of energy sound waves are also large. In addition, the acoustic waves in the dissemination process, will encounter a variety of obstacles. Obstacle solid, liquid and gas. When sound waves encounter an obstacle, part of the energy is reflected, another part of the energy spread of refraction to produce an internal obstacle. Sound waves are spread by the transfer of momentum, so the sound wave propagation, must contain the spread of energy. Thus, a point sound intensity of energy per unit of time through sound waves perpendicular to the direction of sound propagation per unit area. Powerful sound, showing a strong voice.