What if you could listen to music or a podcast without heard or earphone and without disturbing anyone around you? Or have a private conversation in public without other people to hear him?
A new published in PNAS In January it presents a way to create audible enclaves – Localized Sound Scholarships that are isolated from your environment. In other words, we developed a technology that can create sound exactly where it needs to be.
The ability to send sound that becomes audible only in a specific location can transform entertainment, communication and space audio experiences.
What is the sound?
Sound is a vibration that travels through the air like a wave. These waves are created when an object moves back and forth, compressing and decompressing the air molecules.
The frequency of these vibrations is what determines the tone. Low frequencies correspond to deep sounds like a candy; The high frequencies correspond to acute sounds like a whistle.
Control where the sound goes is difficult due to a phenomenon called diffraction – The trend of sound waves to spread as they travel. This effect is particularly strong for low frequency sounds due to its longer wavelengths, making it almost impossible to keep the sound confined to a specific area.
Certain audio technologies, such as the speakers of parametric matrixcan create Focused sound beams in a specific direction. However, these technologies continue to make sound that is audible throughout their route while traveling through space.
The science of audible enclaves
Researchers have discovered a new way of sending sound to a specific listener: through self-stagable ultrasound beams and a concept called nonlinear acoustics.
O ultrasound refers to sound waves with frequencies above the scope of hearing Human, that is, above 20 kHz. These waves travel the air as normal sound waves, but are inaudible to people. Since ultrasound can penetrate through many materials and interact with objects in unique forms, they are widely used in medical imaging and many industrial applications.
At work, scientists used ultrasound as audible sound bearers. It can transport the sound through the space silently-becoming audible only when desired. How can we do this?
Normally, sound waves They combine linearly, which means they proportionally join in a larger wave. However, when sound waves are intense enough, they can interact non -linearly, generating new frequencies that were not previously present.
This is the key to the new technique: it was used Two beams of ultrasound With different frequencies that, by themselves, are completely silent. But when intersecting in space, nonlinear effects cause them to generate a new sound wave in an audible frequency that would be heard only in this specific region.
It was conceived ultrasonic beams that can bend by themselves. Normally, sound waves travel on straight lines unless something blocks or reflects them.
However, when using acoustic metassuperfcies -Specialized materials that manipulate sound waves-it is possible to shape ultrasound beams so that they fold themselves as they travel. Like the way an optical lens fold light, acoustic metassuperfcies alter the shape of the sound waves path. By accurately controlling the phase of the ultra-sick waves, we created sound paths curves that may circumvent obstacles and find themselves in a specific stard.
The main phenomenon at stake is what is called generation of frequency differences. When two ultrasonic beams of slightly different frequencies, such as 40 kHz and 39.5 kHz, overlap, create a new sound wave in the difference between their frequencies-in this case, 0.5 kHz, or 500 Hz, which is well within the reach of human hearing. The sound can only be heard where the beams intersect. Outside this intersection, the ultrasound waves remain silent.
This means that it can Send audio to a specific location or person without disturbing other people as the sound travels.
Advanced Sound Control
The ability to create audio enclaves has many possible applications.
Audio enclaves can allow a Personalized audio in public spaces. For example, museums could provide different audio guides to visitors without headphones, and libraries could allow students to study with audio classes without disturbing others.
In a car, passengers could listen to music without distracting the driver to listen to the navigation instructions. Offices and military environments could also benefit from speech zones located for confidential conversations. Audio enclaves can also be adapted to cancel noise in designated areas, creating silence zones to improve concentration in workplaces or reduce noise pollution in cities.
By redefining the way sound interacts with space, new possibilities are open for immersive, efficient and personalized audio experiences.
