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What if you could enjoy music or a podcast without headphones and not disturb others? Or have a private conversation in a public place without anyone hearing you?
Our recently published research presents a method for creating audible enclaves — localized pockets of sound separated from the surrounding space. In other words, we have developed a technology that can shape sound precisely where it is needed.
The ability to transmit sound that is only audible in a specific area could change the way we approach entertainment, communication, and spatial audio experiences.
What is sound?
Sound is a vibration that travels through the air as a wave. These waves are created when an object moves back and forth, compressing and decompressing air molecules.
The frequency of these vibrations determines the tone of the sound. Low frequencies are associated with deep sounds, such as a bass drum; high frequencies are associated with sharp sounds, such as a whistle.
Sound consists of particles moving in a continuous wave.
Controlling the direction of sound is difficult because of a phenomenon known as diffraction—the tendency of sound waves to spread out as they travel. This effect is especially pronounced for low-frequency sounds because of their long wavelengths, making it nearly impossible to confine the sound to a specific area.
Some audio technologies, such as parametric array loudspeakers, are capable of producing focused beams of sound aimed in a given direction. However, these technologies still produce sound that is heard along their entire path as they travel through space.
The Science of Audible Enclaves
We've found a new way to deliver sound to a single listener: using self-refracting ultrasound beams and a concept called nonlinear acoustics.
Ultrasound refers to sound waves with frequencies above the range of human hearing, exceeding 20 kHz. These waves travel through the air like regular sound waves but are not audible to the human ear. Because ultrasound can pass through many materials and interact with objects in unique ways, it is widely used in medical imaging and for a variety of industrial applications.
In our study, we used ultrasound as a carrier of audible sound. It can transmit sound silently through space, becoming audible only when desired. How did we achieve this?
Normally, sound waves add up linearly, meaning that they simply combine proportionally into one larger wave. However, when sound waves reach sufficient intensity, they can interact nonlinearly, creating new frequencies that
Sourse: www.livescience.com
