Design and Test of a Feedback Controller for Attenuating Low Frequency Noise in a Room

A single-channel feedback control system is presented for global noise attenuation inside a room. The controller design is based on the compensation filter approach of classical control theory. To demonstrate the global noise attenuation capability of this simple control scheme experimental results of noise control in an office are presented. They show that the positioning of the error microphone relative to the control loudspeaker greatly affects the global noise attenuation performance. If the microphone is placed too close to the control source, the microphone signal is dominated by the near field and little global noise reduction is achieved. If the error sensor is placed further away where the near field has little effect on the microphone signal, noise reductions of about 10 dB can be obtained over low frequency ranges.