APPLICATION OF ACOUSTIC METAMATERIALS IN AUDIO SYSTEMS

Audio systems have become an integral part of our daily lives, transforming the way we hear sound in a myriad of applications, including TV, cinema, laptops, mobile phones, and even AR/VR sets. However, although there have been significant technological advancements in recent years, nearly all of these applications still rely on the same century-old electrodynamic transducer technology. This technology operates based on the fundamental principle of an AC motor, where the electrical signal generates a magnetic field that interacts with a permanent magnet. This interaction produces a force that moves the attached diaphragm back and forth, creating sound waves that propagate through the air. Over the years, the electrodynamic transducer has proven to be an effective technology, and its implementation in loudspeakers has become a ubiquitous component of modern audio systems.

Despite the electrodynamic loudspeakers' ability to reproduce high-fidelity sound at a relatively low cost, the physical design of audio systems has remained largely unchanged since the 1970s, leading to many unresolved problems. Although electrodynamic loudspeakers are commonly used in modern audio systems, their dimensions and directional characteristics are not satisfactory. This can result in poor sound quality, uneven distribution of sound, and the inability to deliver sound to certain areas effectively. As a result, listeners may not be able to fully appreciate the intended audio experience.

Acoustic metamaterials offer a promising solution to the growing need to improve the physical design of audio systems. These complex physical structures are intentionally formulated to engineer the propagation of sound, and over the past two decades, they have demonstrated remarkable capabilities to steer and shape sound fields into various patterns, introducing exotic physical phenomena to an otherwise ordinary system. Compared to traditional methods like digital signal processing (DSP) and multi-element arrays, acoustic metamaterials offer several advantages, including passivity, compactness, and cost-effectiveness. Furthermore, with the advent of 3D printing technology, producing acoustic metamaterial structures that work with airborne audible sound has become much easier, as they can be made of essentially rigid plastic that divides air into different compartments. This facilitates the rapid prototyping of novel metamaterial designs for audio systems, accelerating the pace of progress.

In this dissertation, we explore the use of innovative acoustic metamaterial design principles to address the persistent issues associated with electrodynamic loudspeaker-based audio systems and to elevate the user experience. Specifically, we examine how passive metamaterial structures can be used to modulate the frequency response and provide broadband directivity control of these systems. To achieve our objectives, we use a modeling approach that incorporates the entire sound path, balancing accuracy with computational cost. Additionally, we utilize a computerized algorithm to generate inverse designs that help us achieve our desired outcomes. By leveraging these techniques, we aim to design audio systems that provide users with high-quality sound and an optimal listening experience.