What are audible enclaves? – The Hindu

When sound waves are emitted from a source, like a speaker, they diverge as they pass through the air in a phenomenon called diffraction.
| Photo Credit: Desmond Lian/Unsplash

Audible enclaves are small pockets of sound that are not disturbed by surrounding noise. They are produced by new technologies designed to deliver sounds that only one specific person can hear, even if they are in a crowd.

Sound consists of waves moving through a medium, moving the medium’s particles back and forth. How fast this back-and-forth motion happens determines the sound’s frequency. The faster they move, the higher the frequency of the sound.

When sound waves are emitted from a source, like a speaker, they diverge as they pass through the air in a phenomenon called diffraction. Higher frequency sounds diverge more. Devices called parametric array loudspeakers are still able to create focused ‘beams’ of sound. They emit high-frequency waves modulated with an audio signal. As the waves travel through the air, they self-demodulate to produce a sound wave confined in a narrow beam, audible only to those in the beam’s path.

Audible enclaves go a step further. In a study published on March 17 in Proceedings of the National Academy of Science, researchers in the US reported doing this by using two high-frequency waves of different frequencies. They are inaudible in this form. But when they intersect, non-linear interactions cause them to produce a sound wave at that spot, audible only to people nearby.