Precisely directed audio without headphones? University of Sussex 3D prints the answer

Researchers from the University of Sussex in the UK have 3D printed metasurfaces to make acoustic lenses that focuses sound to an individual.

Led by Dr. Gianluca Memoli, the team has invented an automated camera-speaker system that can deliver a directed acoustic message to a tracked moving target. Creating a spotlight of sound, the directional speaker has potential applications in the entertainment industry, such as creating sonic environments in virtual reality (VR) and custom audio experiences in theatres.

At the technology and media conference SIGGRAPH 2019, the scientists presented this invention to entertainment giants such as Disney and Microsoft

Auto-zooming sound

An auto-zoom optical camera works by identifying a person, extending its objective to zoom into the person’s face, then following the face as the person moves. The team’s auto-zoom acoustic camera works with a similar mechanism, except replacing a light lens with an acoustic objective.

An acoustic objective is formed by two 3D printed acoustic lenses of different focal lengths. By adjusting the distance between lenses in front of the speaker, sound is focused on a selected target. The target’s movements are tracked by an in-house face-tracking software. The software then commands the adjustment of lens separation to match the distance of the target from the speaker.

Directly delivering sound to a person, the researchers’ system requires user consent in order to function. This ensures the technology cannot be used intrusively and ensure sounds would not be directed to an unwilling audience.

The interface of the face-tracking software. Image via University of Sussex.

3D printed acoustic lenses

Additive manufacturing and computational modelling have enabled the development of metamaterials. Microengineered from everyday materials such as wood, glass or plastic,  3D printed metamaterials incorporate unique properties such as electric and pressure-induced shape-shifting. For its superior qualities, metamaterials havebeen applied to build optical devices and a sonic crystal cube.

This latest study from the University of Sussex builds on Dr Memoli’s 2017 research on sonic manipulation in 3D printed metamaterial bricks. “Acoustic metamaterials are normal materials, like plastic or paper or wood or rubber, but engineered so that their internal geometry sculpts the sound going through,” explained Dr Memoli. In his 2017 study, 16 types of 3D printed metamaterial bricks are used to build a metasurface which encodes a delay to sound propagation. 

For the auto-zoom acoustic camera, the metasurface assembled works as a convergent lens for sound. To maximise the transmitted sound, the team optimized the thickness of the array of metamaterial bricks. While the idea of acoustic lenses has been around since the 1960s, this is the first time that lenses of practical sizes similar to those used for light have been explored.

The 3D printed metamaterial acoustic lens. Image via University of Sussex.

Applications of auto focused sound systems

The device means optical design can be applied to acoustics. “By designing acoustic materials at a scale smaller than the wavelength of the sound to create thin acoustic lenses, the sky is the limit in new potential acoustic applications,” Dr Memoli added. 

The process means that immersive soundscapes can be created without headphones in VR. By focusing audio to each individual, the technology can also ensure an optimal listening experience for everyone in the audience i.e. at the cinema or in a theater. The 3D printed acoustic lens can also be used to send personalized alert messages in a crowd.

The researchers plan to expand the system’s capabilities beyond just one direction and over one octave. The system will be scaled up to cover most speech and basic melodies, and eventually to deliver a full piece of music.

From light to sound: prisms and auto-zoom lenses” is co-authored by Gianluca Memoli, Thomas J. Graham, Joshua T. Kybett and Arash Pouryazdan.

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