A Private Audio Experience, No Earbuds Needed
Most personal listening today means plugging in headphones or accepting that those around you will also hear what you hear. A new invention from engineers at Pohang University of Science and Technology (POSTECH) offers a different path: a single-unit speaker called MiPAL that beams audio directly to one person. It does so by merging a parametric acoustic system with two kinds of metamaterials, creating an extremely narrow sound beam that stays on target.
How MiPAL Works
Conventional parametric speakers rely on large arrays containing hundreds of transducers. MiPAL, in contrast, achieves the same focused effect with a single component. Earlier attempts at simpler designs struggled because unintended vibrations allowed sound to scatter. MiPAL solves that with two clever layers: an acoustic metasurface across the front acts like a lens, shaping ultrasonic waves into a tight beam, while elastic meta-elements on the back absorb disruptive vibrations and stop audio from leaking sideways. The result is a speaker that keeps sound where it belongs—in one listener's ear.
MiPAL operates across frequencies from 500 Hz to 10 kHz, spanning more than four octaves of the audible range. Its metamaterial parts are produced with 3D printing. In tests designed to mimic the conditions of airplane passenger seating, the device successfully delivered audio to one individual while nearby seats remained undisturbed. The research team describes it as the first demonstration of metamaterials working in a practical, everyday device.
Looking ahead, MiPAL could enable several new uses:
- watching movies without disturbing others;
- music listening for passengers on public transport, no headphones needed;
- museum visitors hearing individual audio guides near specific exhibits.
If the technology continues to advance, public spaces such as trains, planes, and galleries could offer personalized sound zones where people enjoy their own audio without forcing it on everyone else. Because MiPAL has already succeeded in realistic simulations, the leap toward everyday sound systems may be closer than it seems.