Headphones are great until you have been wearing them for an entire workday. Over-ear pairs can get hot and sweaty after a few hours, earbuds can become irritating, and switching to speakers usually means everyone around you has to hear whatever you are listening to as well.
This is where a new speaker developed by researchers at Pohang University of Science and Technology caught my attention. Called MiPAL, it uses ultrasound to send sound in a tightly focused direction, so one person could potentially listen to music, speech, or other audio without disturbing the people sitting nearby.
So how does it actually work?
A regular speaker spreads sound in many directions. MiPAL works as a parametric array loudspeaker (PAL), which uses ultrasound to send audible content in a much narrower beam. At the center of the system is a single piezoelectric transducer, which creates the ultrasonic waves. As those waves travel through the air, they interact through a process called nonlinear acoustics and produce frequencies that we can actually hear.
The researchers use two types of metamaterials to keep that sound focused. An acoustic metasurface at the front works a bit like a lens, straightening the outgoing waves into a narrow beam. Elastic meta-units at the back reduce unwanted vibrations that could otherwise let sound escape to the sides.
While traditional directional speakers can require dozens or even hundreds of ultrasonic emitters, this MiPAL system achieves the effect with a single transducer, making the hardware much simpler.
Where this could actually be useful
The researchers tested MiPAL with both speech and music across a frequency range of 500Hz to 10kHz. They also recreated an aircraft seating setup, where one passenger could theoretically listen to music or an announcement without the person in the next seat hearing much of it.
Planes and trains are obvious use cases, but I can see this being just as useful at a desk. A speaker could play audio directly toward one person without forcing everyone else in the room to listen along. Museums and exhibitions could also use it to deliver audio only to visitors standing in front of a particular display.
Directional audio itself is not completely new. We previously covered the Noveto N1, which used ultrasound and head tracking to create small pockets of sound around a listener’s ears. MiPAL takes a different approach by doing the job with a single ultrasonic transducer and a much simpler hardware setup.
There is still a catch. The researchers say the current prototype cannot yet reach the sound levels of a conventional speaker, so it is nowhere near ready to replace the headphones sitting on my desk. But if the technology eventually gets there, this is one audio experiment I would genuinely like to try.
