Browsing by Author "Lai, JW"

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Broadband spatially feedforward active noise control algorithms using a comb filter
(2003-01-01)
Bai, MSR
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Lai, JW
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機械工程學系
;
Department of Mechanical Engineering
A controller composed of a nonrecursive filter and a recursive filter is used to approximate the ideal controller for a spatially feedforward duct ANC problem. The nonrecursive part represents the dynamics of the transducer, whereas the recursive part is in the form of a comb filter. The parameters of the comb filter are obtained from the impulse response of the controller by using the least-square method. The comb filter is then cascaded with the nonrecursive part implemented as either a fixed filter or an adaptive filter. In the latter approach, two types of LMS-based algorithms are used. The proposed algorithms are implemented on the platform of a digital signal processor Experimental results showed that the approximated controller attained 17 dB maximal attenuation in the frequency band 200similar to600 Hz.
Reduction of electronic delay in active noise control systems - A multirate signal processing approach
(2002-02-01)
Bai, MR
;
Lin, YP
;
Lai, JW
;
機械工程學系
;
Department of Mechanical Engineering
Electronic delay has been a critical problem in active noise control (ANC) systems. This is true whether a feedforward structure or a feedback structure is adopted. In particular, excessive delays would create a causality problem in a feedforward ANC system of a finite-length duct, This paper suggests a multirate signal-processing approach for minimizing the electronic delay in the control loop. In this approach. digital controllers are required in decimation and interpolation of discrete-time signals. The computation efficiency is further enhanced by a polyphase method, where the phases of low-pass finite impulse response (FIR) filters must be carefully designed to avoid unnecessary delays. Frequency domain optimization procedures based on H-1, H-2, and H-infinity norms, respectively, are utilized in the FIR filter design. The proposed method was implemented by using a floating-point digital signal processor. Experimental results showed that the multirate approach remains effective for suppressing a broadband (200-600 Hz) noise in a duct with a minimum upstream measurement microphone placement of 20 cm. (C) 2002 Acoustical Society of America.