A Duct Muffler can make your indoor gardening fans significantly quieter and can reduce the noise heard from room to room. The 4″ Duct Muffler reduces noise by up to 25 dBA; a reduction by 3dBA cuts a listener’s perception of sound by half! This Duct Muffler is easy to install, connect to existing duct work, doesn’t restrict airflow, and requires no maintenance.