NOISE CANCELING SYSTEM

Two microphones spaced along a duct of an air conditioning system provide inputs to circuitry whereby the noise being generated is distinguished from reflected noise. The circuitry imposes a time delay corresponding to the time required for generated noise to pass from the upstream microphone to a canceling speaker. The canceling speaker is driven by the circuitry, subject to the time delay, such that noise at the speaker is canceled by the appropriately driven speaker. In a preferred embodiment movement of the speaker is sensed whereby the actual sound being produced can be compared with the sound required by the canceling speaker driving signal.