US Patent 7894613 Active noise control rack enclosures

Provided is an apparatus and method to control fan noise in a computer server room. An exemplary apparatus includes one or more transducers coupled to one or more walls of a plurality of system racks and one or more active noise control units, wherein the one or more active noise control units send control signals to the one or more transducers to emit a transducer acoustic wave. It also includes a microphone installed near a location in the computer server room where cooling fan noise needs to be controlled, wherein the microphone collects fan noise signals emitted from running fans on the plurality of system racks in the computer server room and sends the collected fan noise signals to the one or more active noise control units to allow the frequency and intensity of the transducer acoustic wave to be substantially equal to a frequency and an intensity of the fan noise and at about 180 degrees out of phase with the fan noise to reduce or to eliminate the fan noise.