Creating audible enclaves: private sound with invisible ultrasound beams
Jiaxin Zhong – Jiaxin.Zhong@psu.edu
Graduate Program in Acoustics
The Pennsylvania State University
Stage College, PA, 16802, United States
Popular version of 1pAA7 – Localized sound reproduction based on nonlinearity-crafted audible enclaves
Presented at the 189th ASA Meeting
Read the abstract at https://eppro02.ativ.me/appinfo.php?page=Session&project=ASAASJ25&id=3979321&server=eppro02.ativ.me
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Imagine sitting in a shared office or hospital room and hearing a message clearly while the people beside you hear almost nothing. Our research shows a way to draw a tiny “bubble” of sound in mid-air—what we call an audible enclave—without using headphones and without filling the whole room with noise. The idea is to start with ultrasound, which is far above what humans can hear, and then make ordinary sound appear only where we want it.
At first glance, readers might think this is the well-known parametric array loudspeaker (PAL), often marketed as an “audio spotlight.” A traditional PAL shoots a narrow ultrasonic beam that slowly converts into audible sound along the entire beam path. That gives strong directionality and long reach, but the audible sound exists wherever the beam travels, like a thin, far-reaching flashlight of audio. By contrast, our system keeps the propagation path essentially inaudible and creates audible sound only inside a small spot. We form two carefully shaped ultrasonic beams that bend around obstacles, such as a person’s head, and meet on the far side. Only in that tiny overlap region does the air’s nonlinearity “mix” the ultrasound and produce normal audio—music, speech, or alerts—right where we place it. Step inside the spot and you hear it; step a few centimeters away and it fades.
In experiments, we produced a palm-sized enclave more than a foot from the source and even behind an obstacle, using a compact emitter roughly the size of a dinner plate. Because the audible conversion is confined to the overlap region, the approach is quiet along the curving paths of the beams and practical in everyday spaces. We also showed that the enclave covers key parts of the speech band, so voices sound intelligible and natural in ordinary rooms rather than only in special lab setups.
This capability could potentially enable private voice prompts in cars or airplanes, confidential bedside communication in hospitals, and personal listening zones in open offices or public kiosks—without headphones and without broadcasting to bystanders. The beams can be bent and steered, so the audible spot appears where needed and avoids where it is not. We are actively improving the system‘s demodulation efficiency and refining the audio quality it delivers.
Schematic depicting the remote creation of an audible enclave. Image adapted from author’s original paper.