Patent ID: 7158644

Claim:
An active noise control system comprising: a noise detector which detects a noise within a duct; an error detector which is provided in a downstream side of the noise propagating within said duct for said noise detector to detect noise within said duct; a control sound source which is installed in the vicinity of said error detector to radiate a control sound having approximately the same sound pressure as of and an opposite phase to the noise within said duct; an arithmetic circuit which inputs an noise signal of said noise detector and an error signal of said error detector, sets a transfer function so that the error signal of said error detector becomes small, multiplies the noise signal of said noise detector with said transfer function, and outputs an multiplied result to said control sound source as a control signal; and a rectifying part which is provided in an upstream side of a fluid flowing within said duct for said noise detector and said error detector, and increases a coherence of the fluid between said noise detector and said error detector by rectifying the fluid within said duct, wherein said rectifying part includes: at least one first rectifying net; a rectifying grid having an opening ratio greater than that of said first rectifying net, and said rectifying grid placed in said duct downstream of and spaced from said first rectifying net; and at least one second rectifying net having an opening ratio smaller than that of said rectifying grid, and said second rectifying net placed in said duct downstream of and spaced from said rectifying grid.