Intake silencers effectively reduce the noise and destructive low frequency pulsations that can be detrimental to surrounding equipment and personnel,
as well as neighbors. The noise and/or pulsation energy generated at the blower inlet is a function of both blower speed and blower size.

It is an established fact that the smaller size blowers do not develop destructive low frequency pulses, whereas larger blowers do. To properly eliminate
these destructive pulsations, a chamber type silencer with a minimum volume of 12 to 15 times the blower displacement is required. This parameter has been incorporated in all application recommendations employing chamber type intake silencers.

Blower speed plays an important part in the correct selection of a silencer. For slow speed blowers, the chamber type silencer performs best on all sizes. For applications not requiring this degree of silencing on small size blowers, the absorption type silencer has been used successfully for many years.

For high-speed blowers (i.e., blowers with operating speeds above the transition speed) a chamberabsorption type silencer is required. This combination design is necessary to reduce the increased high frequency noise energy that is developed above the transition speed and also effectively treat the energy contained in the low frequencies.

Normally acceptable inlet silencer pressure drop is in the range of 3 to 8 inches of water. All inlet silencers will meet this criteria if properly sized in accordance with this bulletin.