Tuning the Sound Field of an Electrodynamic Loudspeaker Using a Horn-like Acoustic Metamaterial Lens

Abstract

Electrodynamic transducers, which are commonly called loudspeakers, are electromechanical devices that convert an electrical current into an acoustic wave. These technologies, for example, are found in headphones, cellphones, and televisions---essentially any public address system or airborne sound communication instrument. Some disadvantages of a singular transducer are the inability to control the radiated field generated by the loudspeaker, and the directional nature of the source as the emitted wavelength becomes comparable to the size of the oscillating surface. Sometimes several transducers are implemented in an array to overcome these limitations, but this inherently increases the geometric size of the radiating array, consumes more electrical energy, and requires complex signal processing to control the sound waves, while still not addressing the directional nature of the sources. Alternatively, acoustic lenses have been introduced to control the sound field of a loudspeaker, but their complex, narrowband, and bulky designs have not found an impactful application since their inception. However, with the increasing efficiency of 3D-printing and the conceptualization of acoustic metamaterials, compact, broadband, cost effective, and complex acoustic lenses can be engineered. This thesis derives and details the creation of such an acoustic metamaterial lens that is constructed of thousands of tiny acoustic horns to control the radiated sound field in various ways from one geometrical design for a singular electrodynamic transducer.