Duct Muffler 10 Inch. Finally a Duct Muffler that can make their indoor gardening fans significantly quieter, and can reduce noise heard from room to room.The Duct Muffler, available in 6 inch,10 inch, and 12 inch sizes (for use with same-size ductwork) reduces noise by up to 25 dBA - a reduction by 3dBA cuts a listeners perception of sound by half! These Duct Mufflers are easy to install, connect to existing ductwork, do not restrict airflow, and require no maintenance. Support brackets not included.