Fantech LD 4 Silencer 4" Duct Galvanized Steel Silencer for use in Kitchen Range Hood Ventilation and Other Applications Were Noise is a Concern. A Fantech Silencer Can Typically Reduce the " Perceived" Sound Level of the System by More than 50%. Units Feature Rubber Seal On Inlet and Outlet. Feature and Specification Sound Data: 8 Suppression dB for 125 Hz