Some applications demand a high airflow while others require minimal noise. To meet these various requirements, fans are available in different speeds. Increases in the fan speed are positively correlated with higher airflow and noise. Note that this positive correlation applies to all brands of fans.

 

High Speed [HS]

            

High speed fans have a higher airflow but are noisier. By designing the impeller to spin faster, the fan delivers higher levels of air relative to other fans with the same case size. Consequently, increasing the fans speed generates more friction in the bearings which creates more noise. Fans categorized as HS or high speed are designed for applications that demand a high airflow; and the increase in noise level is acceptable.

Low Speed [LS]

            

Low speed fans are quieter but deliver less airflow. By designing the impeller to spin slower, the fan becomes relatively quiet to other fans with the same case size. Consequently, decreasing the fans speed also causes less air to be moved by the slower spinning blades. Fans categorized as LS or low speed are designed for applications that require minimal noise; and the lower airflow is acceptable.