No abstract

This paper presents an active noise control system with a combined feedback–feedforward configuration, which may be useful when the location and directivity of the primary source in a room are not known. Using the combined system, the need to choose between a feedforward or a feedback system configuration beforehand is avoided. The optimum performance of feedforward, feedback, and the combined active control systems have been calculated from measurements taken in a 7×6×3 m3 room with various primary source positions. Internal model control (IMC) together with optimal Wiener filtering are used in the design of the optimum controllers, which was performed for each primary source position and also included robust stability to guarantee the stability of the controllers in face of plant uncertainty. The performance of the feedforward controller alone was much more dependent on the position of the primary source than that of the feedback controller alone, but the combined system always performed better than either of those systems. The results also suggested that the combined system could obtain good performance even if the response of its feedback controller was fixed, independently of the primary source location, but the response of its feedforward controller was adapted for different primary source positions.

No abstract

No abstract

Abstract-In general the audible sound has the characteristics of spreading, however the ultrasound is directional. This study used amplitude-modulating technique for an array of 8 ultrasonic transducers to produce directional audible sound beam. In this study sound field distribution for the directional audible sound beam has been investigated. The effect of different weightings varied with different frequency for the transducers on the directivity of the sound beam has also been evaluated. An optimization method was used to calculate the optimal weightings of the transducers for better directivity of the sound beam. Different optimal weightings also added to the carrier and sideband frequencies to control the difference frequency's beam width and side lobe amplitude. The results showed that the beam width can be controlled and good directivity of the sound beam can be obtained by using the optimization method.