A team of researchers at the Penn State College Engineering have created ‘audio enclaves’, a localised pocket of sound zones which one listener can hear in an enclosed space while others nearby cannot.
The team of researchers, led by Yun Jing, professor of acoustics, Penn State College of Engineering, precisely narrowed where sound is perceived by creating localised pockets of sound, titles audio enclaves, to create a ‘private’ listening experience even in an enclosed space such as a vehicle or standing directly in front of the audio source.
The researchers detailed how emitting two nonlinear ultrasonic beams creates audio enclaves, where sound can only be perceived at the precise intersection point of two ultrasonic beams.
Jing explains: “We use two ultrasound transducers paired with an acoustic metasurface, which emit self-bending beams that intersect at a certain point.
“The person standing at that point can hear sound, while anyone standing nearby would not. This creates a privacy barrier between people for private listening.”
Neither beam is audible on its own, requiring the intersection of the beams together to create a local nonlinear interaction, generating audible sound. The beams can bypass obstacles, such as human heads, to reach a designated point of intersection.
The researchers used a simulated head and torso dummy with microphones inside its ears to mimic what a human being hears at points along the ultrasonic beam trajectory, as well as a third microphone to scan the area of intersection.
The sound was not audible except at the point of intersection, creating what the researchers call an enclave.
Researchers tested the system in a common room with normal reverberations, meaning the system could work in a variety of environments, such as classrooms, vehicles or even outdoors.
The system in its current form allows the researchers to remotely transfer sound approximately one metre away from the intended target, with a sound volume of approximately 60 decibels, equivalent to speaking volume. The distance and volume may be increased if the researchers can increase the ultrasound intensity.
Photo caption: Jia-Xin "Jay" Zhong, a postdoctoral scholar of acoustics at Penn State, used a dummy with microphones in its ears to measure the presence or absence of sound along an ultrasonic trajectory. Credit: Poornima Tomy/Penn State.