Patent ID: 7190796

Claim:
A system for actively damping low-frequency coloration of sound comprising: a listening room including a sound source, said listening room defining at least one mode of low-frequency coloration attributable to said listening room; an acoustic wave sensor positioned within said listening room, wherein said acoustic wave sensor is operative to produce a first signal representative of said at least one mode of low-frequency coloration; an acoustic wave actuator responsive to a second signal and positioned within said listening room; and an electronic feedback controller defining an input coupled to said first signal and an output, wherein said electronic feedback controller is operative to generate said second signal at said output by applying a feedback controller transfer function to said first signal, said feedback controller transfer function comprises a second order differential equation including a first variable representing a predetermined damping ratio and a second variable representing a tuned natural frequency, said second variable representing said tuned natural frequency is selected to be tuned to said at least one mode of low-frequency coloration, said feedback controller transfer function defines a frequency response having a characteristic maximum gain substantially corresponding to the value of said at least one mode of low-frequency coloration, said feedback controller transfer function creates a 90 degree phase lead substantially at said at least one mode of low-frequency coloration, said feedback controller transfer function is augmented by the inverse of an acoustic wave actuator transfer function of said acoustic wave actuator to produce an augmented feedback controller transfer function, and said augmented feedback controller transfer function is as follows: V ⁡ ( s ) P ⁡ ( s ) = G ⁢ s 2 + 2 ⁢ ⁢ ζ s ⁢ ω s ⁢ s + ω s 2 s 2 + 2 ⁢ ⁢ ζ ⁢ ⁢ ω n ⁢ ⁢ s + ω n 2 where the units of V(s) corresponds to said rate of change of volume velocity, P(s) corresponds to the pressure at the location of said acoustic wave sensor and said acoustic wave actuator, s is the Laplace variable, ζ represents a damping ratio of an acoustic damping controller, ζ s represents the damping ratio of said acoustic wave actuator, ω n is said tuned natural frequency, ω s represents the natural frequency of said acoustic wave actuator, and G is a gain value.