A comparison of open-loop feedforward and closed-loop methods for active noise control using volume velocity minimization

This paper focuses on the application of the concept of volume velocity min imization to lower the sound generated by a vibrating surface. The motion o f a vibrating surface is measured using an accelerometer, and a speaker is driven so that the net volume velocity of the two is lowered. This concept is tested on a two-speaker system. One speaker acts as the noise source, an d the other as the control speaker (noise suppressor). Using this system, t he effectiveness of three control strategies are evaluated-open-loop feedfo rward, closed-loop proportional, and closed-loop optimal control. The feedf orward system gives noise reductions of 5-25 dB over the range from 100 to 800 Hz. The closed-loop systems give reductions of 5-30 dB over the range f rom 175 to 800 Hz. The feedforward system is found to have the best perform ance below the suppressor's first resonance, while the closed-loop systems have best performance near the first resonance. Speaker coupling is found t o have little effect on system performance. (C) 1998 Elsevier Science Ltd. All rights reserved.