Patent ID: 8418804

Claim:
Multiple Helmholtz resonators for filtering sound in a duct having a neck aperture, comprising: an immovable Helmholtz resonator adapted for physically connection to the duct adjacent to the neck aperture and acoustically coupling to the sound in the duct through the neck aperture; a movable laminate plate movably coupled to the immovable Helmholtz resonator and forming part of the immovable Helmholtz resonator, the movable laminate plate having a neck aperture; a motorized wheel in contract with the movable laminate plate and moving in response to control signals; a movable Helmholtz resonator mounted on the movable laminate plate adjacent to the neck aperture in the movable laminate plate and acoustically coupled to the immovable Helmholtz resonator, the plate being movable between a first position in which the movable Helmholtz resonator is out of alignment with the immovable Helmholtz resonator, whereby the immovable Helmholtz resonator functions as a single Helmholtz resonator dampening sound in the duct, and a second position in which the movable Helmholtz resonator is aligned with the immovable Helmholtz resonator, whereby the movable and immovable Helmholtz resonators function as two Helmholtz resonators in series dampening sound in the duct; an input microphone adapted for coupling to the duct for producing input signals corresponding to sound in the duct prior to acoustic filtering; an error microphone adapted for coupling to the duet for producing error signals corresponding to sound in the duct after acoustic filtering; and a controller receiving and detecting differences between the input signals and the error signals to produce the control signals, the controller transmitting the control signals to the motorized wheel to control the motorized wheels to position the movable laminate plate and the movable Helmholtz resonator.