Technical Paper
Engine Noise Reduction Using Narrowband Feedback Control
1995-05-01
951300
A narrowband feedback control is developed to cancel periodic noise. The method consists of digital bandpass filters centered at a reference frequency and its harmonics. Each of these bandpass filters is then followed by a finite impulse response (FIR) filter which changes the phase of the control signal to achieve the 180° phase shift in the open loop system. A gain is applied to the control signal to adjust the overall noise reduction, considering reasonable stability margins in the system. In a set of experiments the proposed technique was compared with the filtered-x adaptive feedforward control method. The periodic noise, introduced by a noise speaker, inside a reverberant box was controlled (reduced) using both techniques. With the gain properly adjusted, the amount of noise reduction at the microphone was slightly less than that achieved by the filtered-x adaptive control, but the stability characteristics of the feedback control system was considerably better.