At a Glance
- A DIY ultrasonic “sound laser” beams music so only targets inside a narrow path can hear it
- The 40 kHz carrier wave self-demodulates in mid-air, dropping the ultrasonic tone and leaving audible music
- Health agencies have cleared high-power directional ultrasound above 110 dB, but safety reviews may reopen
- Why it matters: The gadget hints at private audio without headphones-and fresh privacy questions
A homemade gun-shaped device can fire a tight column of ultrasound that carries music across a room, letting anyone inside the beam hear tunes while bystanders a step away hear nothing. Megan L. Whitfield reported for News Of Fort Worth that the demonstration, posted by the YouTube channel Electron Impressions, shows the contraption locking onto a camera lens: music blares when aimed head-on, then cuts to silence the instant the barrel drifts off target.
How a Sound Laser Works
Lasers dazzle because their light waves share one wavelength and march in phase. The YouTube build copies that coherence with 40 kHz ultrasound-far above human hearing-so the waves stay in tight formation as they travel. If those waves were audible, the concentrated amplitude would roar like a jet; instead, the frequency keeps the energy inaudible and, regulators argue, safer for directed-audio devices.
From Ultrasound to Audible Music
Listeners in the clip clearly hear a song, yet the emitter never wavers from its 40 kHz tone. The trick lies in the carrier-wave method familiar to radio engineers:
- The device impresses the music’s waveform onto the ultrasonic carrier
- The combined signal rockets through the air in a pencil-thin column
- Non-linear interaction with the atmosphere strips away the 40 kHz backbone
- What remains is the original audio, arriving as if from an invisible speaker suspended in space
Electron Impressions sums it up: “The air itself demodulates the signal, creating audible sound in mid-air.”
No Headphones, No Speakers, No Receiver
Traditional wireless audio needs a radio, a phone, or at least a Bluetooth bud. Here, nothing sits on the listener’s body. The sound materializes only where the beam intersects eardrums, making the experience feel, in the creator’s words, “almost as if the sound is being generated inside their head.”
Regulatory Green Light-for Now
Health bodies in several countries have signed off on directional ultrasound systems above 110 dB for commercial applications like museum exhibits and retail kiosks. The project’s write-up, however, flags that regulators may revisit that exposure limit as more powerful DIY versions emerge.
Viewer Reactions Run Wild
Commenters under the video are trading tongue-in-cheek plans for covert greetings, private museum tours, and pranks that whisper into a single person’s ears. No misuse has surfaced, but the demo revives talk about acoustic privacy in public spaces.
Inside the Build
Electron Impressions has not released schematics, yet the footage reveals:
- A rifle-style grip and trigger for easy aiming
- A compact ultrasonic transducer array at the muzzle
- On-board amplifier circuits powered by a small lithium pack
- A laser pointer for precise beam alignment during tests
Why the Beam Stays Narrow
Ultrasound’s short wavelength-about 8.6 mm at 40 kHz-diffracts far less than bass sound. The result is a beam that spreads only a few degrees, keeping audio energy focused much like a flashlight rather than a booming room speaker.
Safety Limits at a Glance
| Exposure Level | Regulatory View |
|---|---|
| Under 110 dB | Generally cleared for public directional audio |
| Over 110 dB | Approved under specific commercial guidelines, subject to review |
Key Takeaways
- A YouTube creator has proven that a pocket-sized ultrasonic emitter can pipe music privately across open air
- The breakthrough exploits the atmosphere’s ability to peel the carrier frequency, leaving only the song behind
- Regulators already allow high-intensity directional ultrasound in public venues, though standards may tighten
- Expect renewed debate on sonic privacy as DIY guides proliferate
