Imagine being able to listen to your favorite music without disturbing those around you, all without using headphones. This is now a reality thanks to groundbreaking research by a team at Penn State University, led by acoustics specialist Professor Yun Jing from the Penn State College of Engineering. Their concept, called "sound enclaves," paves the way for a new approach to personal audio.
The Concept of Sound Enclaves
Sound enclaves are localized zones where sound is perceptible only at specific points, even in confined spaces like a car or a closed room. This technology is based on the emission of two nonlinear ultrasonic beams that intersect at a designated point. At this point of intersection, a local nonlinear interaction generates an audible sound, while nearby individuals hear nothing. As Professor Jing explains: *"A person standing at this point can hear the sound, while someone nearby would not. This creates a privacy barrier between people for private listening."
The Underlying Technology
To achieve this result, researchers used two ultrasonic transducers combined with an acoustic metasurface— a type of acoustic lens made up of millimeter- or submillimeter-scale microstructures that alter the direction of sound. These 3D-printed metasurfaces allow ultrasonic waves to follow a crescent-shaped trajectory until they intersect. Notably, each individual ultrasonic beam is inaudible; it is their intersection that creates a local nonlinear interaction, generating an audible sound.
Potential Applications and Future Prospects
This technology could revolutionize how we listen to music or podcasts, enabling private listening without headphones in classrooms, vehicles, or even outdoor spaces. Currently, the system can transmit sound to a target about one meter away at a volume of approximately 60 decibels, equivalent to a normal conversation. Researchers believe that both distance and volume could be increased by enhancing the ultrasound intensity.
This innovation paves the way for new applications in the audio field, providing solutions for private listening without bulky accessories. What other uses do you envision for this technology in everyday life?
