The radiation pattern of an acoustic source is naturally directional at high frequencies as the emitted wavelength becomes comparable to the size of the oscillating surface. Directional sound-fields are unfavorable in circumstances where sound source quality is necessary for communicating important and urgent messages to a large population, measuring the acoustic impulse response of a room, or listening to a concert at a venue. Additionally, due to this beaming, a loudspeaker’s bandwidth is strictly limited. This introduces several transducers varying in size and reproductive capability to fully cover the bandwidth. Acoustic lenses have been a solution to altering the sound-field of acoustic sources, but their complex, narrowband, and bulky designs have not found an impactful application since their inception. However, with the expanding efficiency of 3-D printing and the introduction of acoustic metamaterials, compact, broadband, cost-effective, and complex acoustic lenses can be engineered. Discussed here is an acoustic lens that utilizes twisting horn-like labyrinthine metamaterials to alter the directional sound-field emitted from a loudspeaker. Experimental validation, including 2-D and 3-D simulation of the source and lens, is presented to motivate the utility of an acoustic metamaterial lens in producing an omnidirectional sound-field from a directional source.
Hernandez et al. (Tue,) studied this question.