The loudspeaker on your home entertainment equipment is designed to project audio around the space in which it operates, if it’s not omnidirectional as such it can feel that way as the surroundings reflect the sound to you wherever you are. Making a directional speaker to project sound over a long distance is considerably more difficult than making one similar to your home speaker, and [Orange_Murker] is here with a solution. At the recent Hacker Hotel conference in the Netherlands, she presented an ultrasonic parametric speaker. It projects an extremely narrow beam of sound over a significant distance, but it’s not an audio frequency speaker at all.
Those of you familiar with radio will recognize its operation; an ultrasonic carrier is modulated with the audio to be projected, and the speaker transfers that to the air. Just like the diode detector in an old AM radio, air is a nonlinear medium, and it performs a demodulation of the ultrasound to produce an audio frequency that can be heard. She spends a while going into modulation schemes, before revealing that she drove her speaker with a 40 kHz PWM via an H bridge. The speaker itself is an array of in-phase ultrasonic transducers, and she demonstrates the result on her audience.
This project is surprisingly simple, should you wish to have a go yourself. There’s a video below the break, and she’s put all the files in a GitHub repository. Meanwhile this isn’t the first time we’ve seen a project like this.
Is this something that can be coupled with a camera and a computer to do facial recognition and target the audio to one specific person? I’m getting quite annoyed by a coworker always using a large speaker in the workplace to play music I’d normally take active steps to avoid listening to.
I hate to say it but I think the technology you are missing is called “personal confrontation.” It still has a few bugs to work out…
At least it’s like any other buggy tech, a couple of firm slaps and a punch usually fix the issue.
A percussive solution to an acoustic problem? I like it!
Weren’t there a couple of articles here about using this tech to do ghost writing and localized sound fields?
Could we use the ghost writing one to make a co-worker to vaguely feel like something’s crawling on them or some other sort of feeling of being touched?
Or do like the military and beam the voice of their supreme being into their work zone.
I would sweat for my MOSFETs driving an array of piezos like that. A transformator in between would be way more efficient
A square array for this seems like an odd choice. With that many transducers a 91-element hexpack forming a pseudo-circular array would generate better-behaved sidelobes. Video says the transducers are all wired in parallel, so there’s no apodizing either.
A great start. Several possible improvements were mentioned. The obvious next step is individual element drive to make a phased array.
Yah. So maybe blasting your coworkers, even the really jerky ones, with an array of ultrasonics isn’t the best approach?
I did some quick research for studies on the safety of this tech.
Focusonics, who manufacture these things commercially mention a single study that found “no adverse affects.” They don’t actually cite to the study.
Given that these things are primarily used by the military for crowd dispersal I’m not sure building a big array of ultrasonics and blasting them at people is the best idea.
Focusonics also claims that because humans can’t hear above 20khz it shouldn’t be an issue. Ergo, if I don’t see UV and I don’t feel radiation presumably not a problem?
My point is that are like no broad studies of longterm effects of these things. Hearing loss takes a long time to manifest but it’s usually totally irreversible.
Not to discount the (real) concerns, but “primarily used by the military for crowd dispersal” Is that correct? Not confusing with the so-called Active Denial System that uses millimeter-wave radio frequency energy?
LRAD system. Also used on ships to scare off pirates. Really loud directional speakers with horrible sounds to disperse crowds.
Sounds perfectly fine for me.
Live by the sword, die by the sword.
Got some friend who (and his whole neighbourhood) is in legal battle for years with a campsite owner that decided to move its sound system next to the houses for no reason.
Previous installation was 200 m away and caused no troubles.
I suggested to my friend to build such a device to ping back the noise to the speaker with a delay. It looks like it’s very confusing. And we hope it could stop the trouble.
I feel its pain because I got through much much worse. Noises could lead you to the edge of despair. And there’s so little you could legally act against.
This.