Assessment of a practical technique for active control of sound using microphone and speaker

In this analytical study, it has been desired to develop a practical and simple control mechanism to control, at a given point and its neighborhood, the sound arriving from a distant source, assuming that a primary pure-tone sound pressure is propagated from a relatively far distance. The control model consists of a microphone as a sensor for measuring the sound pressure and a loud speaker for applying the control force. Corresponding equations have been developed to determine an optimum control force, and afterwards a parametric study on the factors affecting the control results has been performed. The results show that the control system can significantly reduce low frequency sound pressure in the region near the target point. The results also demonstrate less effectiveness in controlling high frequency sound pressures. Moreover, the larger the distance of the loudspeaker to the given controlled point is, the wider the controlled area will be. Also, it was found that though the distance between the sensor and the actuator does not have any effect on the size of the area which can be controlled, such distance is of greatest importance in that the available time to control increases directly by increasing the distance.