Ultra-broadband acoustic metamaterial lens for loudspeaker directivity control

Acoustic metamaterials have been utilized to manipulate the direction of sound propagation, but their practicality in audio engineering has been significantly constrained by their narrow effective bandwidth. In this paper, we introduce an ultra-broadband acoustic metamaterial lens that can omnidirectionally emit sound between 1000 and 10 000 Hz when positioned in front of a 4-in. full-range driver. We also demonstrate that the same method can be employed to create a broadband sound-focusing lens with a consistent directivity pattern between 2000 and 20 000 Hz. The metamaterial lens is advantageous in any situation where broadband passive control of loudspeaker directivity is desired.