Acoustic Innovation Routes Sound Waves Across Space for Personal Audio Experience Without Headphones
Craving an immersive, personalized audio experience without the hassle of headphones? Look no further! Our revolutionary research unveils the creation of audible enclaves – pocket-sized sound zones that cater to your listening needs without disturbing others.
What makes sound tick?
Sound is essentially a wave that vibrates through air. These waves are produced when an object moves back and forth, causing air molecules to compress and decompress. The frequency of these vibrations sets the pitch — low frequencies bring deep, bass-like sounds, and high frequencies evoke sharp tones like a whistle.
Shaping sound is a tricky business, thanks to a pesky issue called diffraction. This phenomenon causes sound waves to scatter as they travel, making it difficult to contain them within a specific area, especially for low-frequency sounds.
Enter high-tech audio systems like parametric array loudspeakers, which create focused sound beams. Although these babies can be pointed in a specific direction, they still emit sound along their entire trajectory.
The science behind audible enclaves
We've stumbled upon an ingenious solution: using self-bending ultrasound beams and engaging a concept called nonlinear acoustics.
Ultrasound refers to sound waves above the human hearing range (20 kHz and beyond). These sound waves travel through the air like normal sound waves but are invisible to the human ear. Due to their versatile properties, ultrasound is widely utilized in various fields, including medical imaging and industrial applications.
In our groundbreaking discovery, we employed ultrasound as a silent carrier for audible sound. This unique method allows sound to travel undetected until it reaches the desired location. How?
Here's the deal: Normally, sound waves combine linearly, following the rule of proportionally adding up. However, when sound waves are sufficiently intense, they interact nonlinearly, generating new frequencies that weren't present in the original signal.
This interaction is the secret ingredient to our technique: We use two ultrasound beams with slightly different frequencies (e.g., 40 kHz and 39.5 kHz) that are completely silent on their own. When they cross paths, however, nonlinear effects cause them to produce a new sound wave at an audible frequency, which is only heard in the intersection area.
The cherry on top? We designed ultrasonic beams that can bend autonomously. Traditionally, sound waves travel in straight lines unless blocked or reflected. By using acoustic metasurfaces — specialized materials that modify sound waves — we can manipulate ultrasound beams to bow as they travel. Similar to how an optical lens bends light, acoustic metasurfaces change the sound wave's trajectory. By fine-tuning the ultrasound waves' phase, we construct curved sound paths that dodge obstacles and converge at a specific target.
The magic lies in difference frequency generation: When ultrasonic beams of differing but adjacent frequencies overlap, they generate a new sound wave at the difference between their frequencies, which falls within the human hearing range. Sounds can only be heard where the beams cross, leaving the path silent outside of the intersection.
This means you can share your favorite tunes or conduct private conversations without disturbing others as the sound journeys to its destination.
The future of sound!
Audio enclaves have enormous potential applications:
- Personalized audio experiences in public spaces, such as museums and libraries
- In-car entertainment that considers driver safety
- Confidential conversations in offices and military settings
- Noise-canceling zones in workplaces and urban areas
Although our technology still faces challenges — like nonlinear distortion and power efficiency issues — the prospect of tailor-made audio experiences is undeniably exciting! The future of sound awaits as we continue to redefine how it interacts with space.
Contributors
Jiaxin Zhong, Postdoctoral Researcher in Acoustics, Penn State, and Yun Jing, Professor of Acoustics, Penn State. This article is republished from The Conversation under a Creative Commons license. Read the original article here.
Enrichment Data Summary:
- Nonlinear acoustics is crucial for creating the audible sound only at the intersection point of the beams, ensuring privacy.
- Self-bending ultrasound beams can be shaped using acoustic metasurfaces to bypass obstacles, allowing sound delivery even behind human heads.
- Acoustic metasurfaces enable precise control over sound beam paths, ensuring beams converge at a specific target location for audible enclaves.
- Difference frequency generation is the key phenomenon that enables audible sound by combining slightly different ultrasound frequencies.
Sound waves combine nonlinearly when they are sufficiently intense, generating new frequencies and enabling difference frequency generation. This phenomenon is crucial for creating audible sound only at the intersection point of ultrasonic beams, ensuring privacy in audible enclaves.
Acoustic metasurfaces, a type of specialized material, are used to manipulate ultrasound beams and modify their trajectories, allowing self-bending and precise control over sound beam paths for audible enclaves.
By using ultrasonic beams with slightly different frequencies that converge at a specific target, our innovative technology creates focused sound zones called audible enclaves, ensuring personalized audio experiences without disturbing others.
In the future, audible enclaves have enormous potential in various fields, such as personalized audio experiences in public spaces, in-car entertainment, confidential conversations in offices and military settings, and noise-canceling zones in workplaces and urban areas.
