초록 ▼

An active acoustic attenuation system for attenuating tonal blade pass noise in a multi-bladed fan uses a sinusoidal rotational speed signal produced by an accelerometer mounted on the fan as the reference signal for a filtered-X LMS (least mean squarae) adaptive filter controlling a canceling sound

An active acoustic attenuation system for attenuating tonal blade pass noise in a multi-bladed fan uses a sinusoidal rotational speed signal produced by an accelerometer mounted on the fan as the reference signal for a filtered-X LMS (least mean squarae) adaptive filter controlling a canceling sound generating speaker. The sinusoidal signal is clipped by a zero crossing detector to produce a rectangular wave signal having harmonics which include the fundamental and harmonics of the tonal noise to be eliminated. When the system is used with axial flow fans having a central hub, the speaker is mounted facing the fan and coaxial with the hub. When the fan has a straight discharge conduit, the speaker is no larger in diameter than the fan hub to preclude restricting flow; however, there is no restriction on the size of a speaker facing the fan when it is mounted in the rear wall of a discharge chamber having a lateral discharge opening.

대표청구항 ▼

An active acoustic attenuation system for attenuating tonal noise associated with a fan having a plurality of blades, said system comprising: an accelerometer mounted on said fan and generating a sinusoidal signal having a frequency representative of the rotational speed of said fan; means clipping

An active acoustic attenuation system for attenuating tonal noise associated with a fan having a plurality of blades, said system comprising: an accelerometer mounted on said fan and generating a sinusoidal signal having a frequency representative of the rotational speed of said fan; means clipping said sinusoidal signal to generate a clipped signal having a fundamental frequency equal to the frequency of rotation of said fan and containing harmonic frequencies of the fundamental frequency of said fan speed which include the fundamental frequency and harmonic frequencies of said blade pass tonal noise; speaker means mounted adjacent said fan and generating canceling sound for combination with and attenuation of said fundamental frequency and harmonic frequencies of the blade pass tonal noise of said fan; an error microphone spaced from said fan and said speaker detecting said combination of tonal noise and canceling sound and generating an error signal therefrom; and electronic controller means responsive to the clipped signal and said error signal for driving said speaker, said electronic controller means including adaptive filter means which accommodates for acoustics delays between said fan, the speaker and the error microphone.