Active control of a finite length line source by a novel secondary source

Abstract

Active control of noise in free space tends to be challenging, especially for the overall attenuation. This paper focuses on the control of a finite line noise source using active approach. Previous study by the author reveals that the introduction of a directional source, an axially oscillating circular piston, as the secondary control source will improve the overall performance of the active noise control system. A novel directional source is theoretically studied in this work, which consists of a core piston and an outer concentric annulus. The two components are axially oscillating with different phases and amplitudes, and these parameters are optimized to maximize the source directivity. This structure can be further extended to add more outer annuluses, which also could be analytically analyzed of the optimal parameters according to the similarity of the construction components. This exquisitely novel control source is adjusted to radiate a sound field analogous to the primary line source with multi-lobe property, and its physical size is restricted within a practical dimension.