Patent ID: 7869607

Claim:
An add-on active muffler adapted to be installed in a server chassis, the add-on active muffler comprising: a duct comprising an inner portion and an outer portion, wherein the inner portion is configured to be disposed within an interior of a server chassis, wherein the outer portion is configured to protrude from the server chassis, wherein the inner portion and the outer portion are contiguous with one another and together comprise the duct for moving air from within the server chassis to without the server chassis; and an active noise control (ANC) system to actively reduce one or more effects of a noise source, the active noise control system comprising: an input transducer to sense an acoustic noise field generated by the noise source, and to generate from the acoustic noise field an input signal; an output actuator to generate an acoustic output field effective to reduce a level of the acoustic noise field; a correction unit to adjust the input signal compensate for characteristics of the input transducer and the output actuator; an echo canceller to remove from the input signal a portion of the output of the output actuator, which comprises a feedback through the input transducer, wherein an output of the echo cancellation unit represents a signal corresponding to the noise source; and an anti-noise generator to generate an anti-noise signal opposite in phase to the input signal by applying an adjustable prediction filer, wherein the prediction filter is adjusted based on a residual noise at a virtual error microphone, which is estimated based on a combination of an estimated error noise at the error microphone and an estimated counter noise at the error microphone, wherein the output actuator is to generate the acoustic output field from the anti-noise signal.