1. Enhance the aerodynamic load of blade lattice and reduce the peripheral speed. For fan with strong forwarding blades and multi- blade impeller, it is beneficial to increase the aerodynamic load of blade lattice. Under the same air volume and air pressure circumstances, the l circumferential velocity on impeller blade circumcircle can make the fan noise be decreased obviously.
2. The reasonable radius of volute tongue clearance and the volute tongue. When air flow relative moves with blade, the velocity and pressure in the air flow wake at the blade trailing edge are  less than mainstream area,  so that the airflow velocity and pressure after the blade lattice are not distributed evenly, the uneven airflow is  rotating,  due to the volute tongue existing at the air output of the moving blades, then  the interaction between the unsteady flow and volute tongue will produce noise, the strong noise can be heard if the distance to the noise is short, Usually take appropriate larger wind tongue front radius to reduce the rotation noise and vortex noise of the centrifugal fan.
3. Inclining of volute tongue. The periodic fluctuating aerodynamic force generating by the periodic fluctuation velocity of the fan impeller and bladder air flow makes the volute tongue interact to produce rotating noise, this noise  amplitude is related with the intensive vibration and the windard area of volute tongue. Tilting the volute tongue can make the effecting area of the fluctuating aerodynamic force reduce , so the radiation noise  is also reduced.
4. Turbulent flow device at impeller inlet(outlet) The entry or exit of the fan impeller blade is provided with turbulence device (wire mesh) , which can enable the laminar boundary layer on the reverse of the blade immediately convert into a turbulent boundary layer, delay the separation of boundary layer on the back of blade, evenly they are not isolated. The blade trailing edge is equipped with wire mesh,  the air velocity and pressure gradient behind the mesh can quickly become even. If the mesh is in the vortex area, it will greatly reduce the vortex area  and can further reduce noise.(ljc)