Computer & AV Cabinet USB-Controlled Cooling Fan System, with Multi-Speed Fan This cooling unit is designed to be mounted inside your equipment cabinet. It will quietly pull the warm air out of your cabinet and exhaust it out the back or top. It has a high-quality, low-noise 120mm fan, with long-lasting and quiet fluid dynamic bearings. The system includes a USB control module, which turns the fan on and off, under the control of your computer or component's USB port (type A connector). The USB module controls the power from the multi-voltage transformer (included with the cooling system), which runs the fan at any one of 5 speeds. IMPORTANT: Please make sure that your computer's USB port turns on (powers up) ONLY when the computer is turned on. That way, the fans will run when the computer is on and turn off when the it is off. Recommended fan speeds: The 120mm fan is rated at 19 db, while moving 55 cubic feet of air per minute (3/4 speed). The fan has approximately these specs at different speeds: 1/3 speed = 25CFM at 10db, 1/2 speed = 37CFM at 13db, 2/3 speed = 49CFM at 16db, and full speed = 74CFM at 22db (approximate). With cabinet cooling, slow (and quiet) are the way to go! The cooling unit measures 6-1/4" square (includes the mounting plate), and the required hole is approximately 4-7/8" square. The fan and back grill are 1-1/4" thick behind the mounting plate, and only require about 1/3" additional space behind the back of the fan for airflow.