A blower fan moves large quantities of air or gas at relatively low pressures, usually measured in inches of water column gauge ("H2O") rather than in pounds per square inch (psi). This air or gas is moved due to the dynamic action of the rotating vanes or blades which impart velocity and pressure to the air or gas.

The noise generated by the rotation of the vanes or blades is fairly balanced across the noise spectrum, with some increase in the first three octave bands. However, due to the function of the human ear the mid to high range of frequencies are heard to be louder and will result in problems with personnel who work nearby and/or those located some distance away. Fan blowers are normally constructed of either cast iron or welded steel plates which do not remove the noise generated by the moving air/gas stream. This noise can be passed on through the piping or ducts which will radiate this noise throughout the system.

Effective treatment of the intake and discharge noise generated by the blower fan is accomplished by using a high volume, low pressure drop, absorption type silencer which can control the noise as a unit. Use of this type silencer eliminates the more costly alternative of lagging or lining the piping or duct work. Silencers can easily be retrofitted into existing blower systems and can be designed into future construction to create more effective noise control.