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Making a rickroll laser: A parametric speaker
- slicktux 2y agoPretty cool! I’ve seen similar implementation in the Elektor 2011 issue magazine. The US navy uses the commercial brand of these speakers; LRAD (long range acoustic device) to ward off pirates at seas. LRAD is the company that makes them for defense purposes and they patented the name and acronym. But parametric speakers are used everywhere even museums and apparently for trolling Rick roll too! :)
- Trevor908 2y agoFwiw lrad is regular speakers. Not ultrasound. Just tweeters.
- jamal-kumar 2y agoThose things are so goddamn loud, I've seen them tested before a bunch. I used to see them for sale on ebay and amazon which was pretty funny. Not anymore. Still on aliexpress, as well as these sound laser directional speakers albeit the LRAD will run you at least 5 grand and you can probably make the directional speaker cheaper as in this DIY project
- nalllar 2y agoIs this dangerous in terms of hearing damage due to the perceived low sound level alongside inaudible louder ultrasound?
- RadiozRadioz 2y agoThis reminds me of when I played around with laser diodes as a kid (of course to burn random things). I ordered a powerful green laser diode from eBay, wired it up and pointed it at some black paper, hit record on the camera, excitedly connected the battery and... nothing. I checked the wiring, all was good. I looked in the end of the diode, I could see a faint red glow inside, but nothing else. I must've got a dud unit. Later I looked at the recording and my heart sank. When past me connected the battery, the room immediately lit up with a bright white glow. The diode emmitted an intense beam of infrared light... and I pointed that thing directly at my eye. There wasn't a wider point to that, this just reminded me and I wanted to share. I suppose be careful of what you can't see. I got lucky. That sort of thing can cause big problems. Especially those that stay unnoticed until old age. Hearing is also one of those.
- vachina 2y agoI guess you should be fine. My face gets blasted with point based IR day in and out by FaceID and Windows Hello and I can still see fine lol.
- wizzwizz4 2y agoCan FaceID or Windows Hello burn things? No? Maybe they're not high-intensity lasers. IR lasers are dangerous. (Well, lasers in general.) Please don't downplay their risks.
- vachina 2y agoCan the laser in OP’s laser burn things? No? Point of my comment is to console OP’s concern with long term damage to his eyes. Some Windows Hello’s IR emitter is powerful enough I can see bright red blinking.
- nihzm 2y agoI have a friend who built one of these as their thesis. IIRC they were telling me that the air through which the sound beam propagates acts as a low pass filter, so if you're at the correct distance from the device the high frequency energy should have dissipated. Interesting stuff, I wish I had more time to learn about what they where doing.
- binary132 2y agoI was thinking about how the air itself must be contributing to the construction of the (standing?) sound wave as a resonator.
- nihzm 2y agoNot sure if there are standing waves involved, or resonance. I presume it is very similar to a phased array [1] for beamforming in antennas, except that then anisotropic properties of medium may not be negligible to construct the wavefront (temperature gradients & wind), which is probably also why these devices do not sound great. To produce a high quality waveform at the receiving end the physics probably becomes quite involved rather quickly. [1]: https://www.analog.com/en/resources/analog-dialogue/articles/phased-array-antenna-patterns-part1.html https://www.analog.com/en/resources/analog-dialogue/articles...
- nothacking_ 2y agoI'm not an expert on this, but there don't seem to be any reported cases of hearing loss from sounds above 30 kHz, but there are documented cases of unpleasant effects. In any case, I'd keep some distance, just to be safe.
- naikrovek 2y agoNo, we don’t hear ultrasonic frequencies because our ears do not resonate at those frequencies. We hear sounds when the cilia in the cochlea resonate with the incoming sound. We don’t have cilia of the length required to resonate with ultrasonic sounds, so there’s no danger of hearing loss. Animals may get their hearing damaged, if they are in the path of the sound, are close enough that it’s still ultrasonic at their location, and are sensitive to the frequency used, I believe. Maybe someone who knows for sure can say for sure.
- HarHarVeryFunny 2y agoAwesome - very cool project!
- tomcam 2y agoThe Country Music Hall of Fame in Nashville has these. Bad sound but the directionality works well. Want one of these in the bathroom so I can take a long shower and listen to podcasts without waking up my lovely wife.
- cjbgkagh 2y agoSurely waterproof headphones would be far easier and sound far better
- tomcam 2y agoYou correct. But I’m clumsy and interrupt-driven. I would somehow forget about them, drop them on the floor, then trip on them and break a hip.
- tomcam 2y agoOK I bought some water resistant bone conduction earphones
- tomcam 2y agoThey work perfectly and hook to my ears so they can’t fall off!
- tomcam 2y agoUpdate: you are correct, the water-resistant bone conduction set works like a charm. And they won’t fall off. I’d say your solution is conservatively .5% what I would have paid for the less satisfying parametric array.
- dylan604 2y agoThey make a "speaker" for loud environments like trade shows or museums that are parabolic dishes. There's a speaker at the node and the dish reflects all of the sound back down into a collimated "beam". The ones I've specifically used were meant to be hung overhead so you only hear it when you step underneath. They were clear acrylic bowls that were 24"-30" diameter. It was mainly meant for delivering dialog/narration to a video playing without annoying the people working the booth. It was effective for the purpose
- Reventlov 2y agoso, basically, beamforming but for sound ?
- graycat 2y agoLasers? Ah, one of the early lasers was He-Ne gas in a narrow tube, a radio transmitter antenna wrapped around the tube (or some such), and mirrors at both ends of the tube. So, photons would go back and forth between the mirrors, a tiny fraction would leak out of a mirror as the laser light, and the rest would stay in tube and help generate more photons from the radio and He-Ne interactions (laser, light amplification via stimulated emission of radiation). So, right, just thinking from the OP, between mirrors there was some highly favorable line of amplification, and that line meant that the beam out of the laser would be an extension of that line and form a "narrow" beam!!! Right, if use some voltage on some piezoelectric crystal to make tiny adjustments in the distance between the mirrors, then will make small changes in the frequency of the light, i.e., there is a highly favorable wavelength that fits a whole number of times between the mirrors or some such. The changes in frequency of the light still have to correspond to the thermally moving gas atoms generating the light. Right, if have the favorable frequency in the middle of the feasable range, will get slightly less power in the beam, a dip, called the Lamb dip. Could that dip be used as a length standard? First job, worked on that, physicist, NIST, then the NBS, US National Bureau of Standards. That is, at the end of the laser we have a tiny light source that puts out a very narrow beam. How? As above and not from antenna theory.
- noodlesUK 2y agoSo how does this work? Is it the same as the kind of phase cancellation that you often see with two speakers playing the same tone, but just with lots of elements (and an ultrasonic source)?
- nihzm 2y agoAs far as I understand yes, I would also guess that it is analogous to a phased array antenna, but with sound waves
- jamal-kumar 2y agoIt's a sound laser, or maybe I'm remembering the video in this link wrong on the terminology and the SASER is different? Maybe it's just "sound from ultrasound" https://en.wikipedia.org/wiki/Phonon https://en.wikipedia.org/wiki/Phonon https://en.wikipedia.org/wiki/Sound_amplification_by_stimulated_emission_of_radiation https://en.wikipedia.org/wiki/Sound_amplification_by_stimula... https://www.youtube.com/watch?v=aBdVfUnS-pM https://www.youtube.com/watch?v=aBdVfUnS-pM https://en.wikipedia.org/wiki/Sound_from_ultrasound https://en.wikipedia.org/wiki/Sound_from_ultrasound
- aidenn0 2y agoThis is not a sound laser; the beam has some similar properties to a laser (e.g. collimation), but it works more like a directional antenna.
- jamal-kumar 2y agoYeah I think you're correct. Really interesting distinction
- deleted 2y ago[deleted]
- night862 2y agoIts quite interesting. The directional ultrasonic array broadcasts a carrier frequency, not unlike am radio. You can read about the function of this sort of device at hackaday. https://hackaday.com/2019/02/14/creating-coherent-sound-beams-easily/ https://hackaday.com/2019/02/14/creating-coherent-sound-beam...
- jamal-kumar 2y agoWhat's really interesting about these piezoelectric ultrasound emitters (Not far off from what you see in novelty fog fountains with the little waterfall and maybe some elves and mushrooms), in different arrangements, are actually capable of something called acoustic levitation of small objects - and what's more this is actually something you can DIY as well https://www.youtube.com/watch?v=yVDWrWpaBho https://www.youtube.com/watch?v=yVDWrWpaBho https://www.instructables.com/Acoustic-Levitator/ https://www.instructables.com/Acoustic-Levitator/ https://pubs.aip.org/aip/rsi/article/88/8/085105/962938/TinyLev-A-multi-emitter-single-axis-acoustic https://pubs.aip.org/aip/rsi/article/88/8/085105/962938/Tiny... https://www.youtube.com/results?search_query=acoustic+levitation+diy https://www.youtube.com/results?search_query=acoustic+levita... There's some interesting applications combining it with projection here (Acoustic holography): https://www.youtube.com/watch?v=Q9GybXczNAc https://www.youtube.com/watch?v=Q9GybXczNAc
- klysm 2y agoThe novelty fog fountains are typically a piezo micro mesh with tiny holes, which is similar but distinct from ultrasonic atomization
- jamal-kumar 2y agoI think you can get them on amazon etc as 'ultrasonic foggers', they're different somehow?
- klysm 2y agoYeah there are two ways I know of to achieve atomization using ultrasonic transducers. 1. Blast water with ultrasonic waves such that the top of the waves break off into droplets. This is well studied in the literature, but you need a decent amount of power to make it work. 2. Metal mesh piezo atomization. This uses the planar vibrational modes of a piezo disc to rapidly shove liquid through tiny holes.
- jamal-kumar 2y ago
- dylan604 2y ago"The beam also bounces off objects, making it seam like the sound is coming from somewhere else. Strangely, the sound is actually louder when bouncing off a hard object like a wall then when listening to it directly. I’m guessing that the surface creates areas of higher ultrasound intensity, creating more sound then would be created otherwise." Would this just be due to the fact that the reflecting surface isn't perfectly smooth so the reflections do not reflect back 180° and pretty much scatter up reflection?
- TeMPOraL 2y agoThat sounds like the thing where you turn your bass speaker towards the wall (ideally a corner) and the bass gets louder/better. A friend showed me this in high school; never figured out how this could possibly work.
- dylan604 2y agosome bass bins are in a folded configuration so that the speakers are not firing directly out of the front of the cabinet but from an angled position that hits the back before exiting the front of the cabinet.
- hunter2_ 2y agoWith low frequencies, directionality is negligible, so it's not about turning it "toward" the wall, but about placing it against the wall. I suppose it's possible that the sound radiates more from one side than the other (possibly the side with the cone, or maybe the side with the port if one exists!) so turning it can result in effectively moving it closer. Or maybe you were listening to a more directional frequency range than I'm thinking of. Anyway, why does closer matter? If you suspend a subwoofer up in the air so it has no boundaries, its sound radiates in all directions (full space). If you put it on the floor (let's assume all such boundaries are infinitely dense and thick, for simplicity) its sound now radiates only upwards/outwards (half space). Now push it up against a wall: quarter space. And finally, put it in the corner of the room: eighth space. Of course for a few millimeters it goes toward the boundary but then is reflected back, and so long as the distance isn't so significant relative to the wavelength that destructive interference (cancellation) occurs within the audible range, all interference is constructive (additive). The SPL in the listening area increases by 3 dB for each of these boundaries/halvings, although in practice it's slightly less since typical boundary material is a little bit acoustically absorptive (sound converts to heat) and acoustically transparent (sound is transmitted through to the other side), but even complete absorption isn't any worse than complete transmission to a place with no listener (i.e. the absence of a boundary): the sound goes unused either way. Fun fact: typically half-space is used when citing the efficiency of a speaker in terms of dBSPL/Watt, since the vast majority of the power is for bass, and it's considered rare to emit bass against fewer than one boundary (the floor). The next time you are deciding where to position your bluetooth speaker, if it's lacking in bass, boundary-load it. But this is all about turning non-directional sound into directional sound (through boundary loading, which is a very close cousin to horn loading, as a sibling comment mentions with folded horn cabinet designs). TFA isn't about that though, it's about sound that's already directional! So I doubt any of what I've said is relevant to this mysterious effect.
- jonway 2y agoI would like to make the unsubstantiated assertion that unscrupulous police and occasionally private entities use this existing technology (available for organizations such as libraries, venues, corporate) off-label on occasion as an “investigative tool”, which is to say maliciously.
- deleted 2y ago[deleted]
- andoando 2y agoShould put these random places in the streets and have them play at random times
- Lammy 2y agoThe security state decrees that this is not a good idea https://en.wikipedia.org/wiki/2007_Boston_Mooninite_panic https://en.wikipedia.org/wiki/2007_Boston_Mooninite_panic
- joezydeco 2y agoI want a compact version I can point out a car window at the glass of another car and turn it into a voice speaker.
- night862 2y agoYou can surely do this and more! The device presents as a panel, however. You need to use an array of transducers to form a coherent sound beam, but it will possibly sound through the window and gain the attention of an occupant, or enter the vehicle and seem to come from inside the car its self. You can also just point them at someone.
- plummox 2y ago[flagged]
- kazinator 2y agoDirectionality is a normally an almost completely unwanted quality in speakers. You want speakers to be heard equally well from all directions (that are frontward of the speaker's baffle). That's one reason why speaker boxes use multiple speakers, and these get smaller for the higher frequency ranges. "Dome tweeters" are shaped as such in order to radiate all around. A "full range" speaker will send the lows in all directions but the highs mainly in the direction of its axis. A listener caught in the beam will hear a shrill sound, whereas someone off axis hears it muffled. Guitar speakers are like this; particularly the 12" ones and particularly in the 4x12 cabinet arrangement. Sometimes musicians use dispersing devices mounted on the speakers, like "beam blockers". Or the speaker is picked up by a microphone close to it, so that the audience hears it fro the PA system (which solves the sound dispersion problems in its own way). There are situations in which it is desirable for a speaker box to "beam", like when it is mounted far away or high above a target listening area that is relatively small, calling for the speaker to be a kind of spotlight.
- numb7rs 2y agoSpeaker directionality gets interesting once you get to arrangements for festivals and concerts. Ideally the audience should all be able to hear well, which is difficult to achieve over such a large area and with multiple sources. But you also don't want the neighbours to complain about the thumping bass. A number of subwoofers pointing backwards, with the right phase delay, destructively interferes with the most offensive frequencies and reduces the sound intensity behind the stage. It's called a 'cardiod' arrangement, because of the shape of the resulting sound intensity distribution.
- deleted 2y ago[deleted]
- ano-ther 2y agoYes. And then you have the vexing problem of the stage sound where you want the musicians to hear themselves and each other. Without feeding back into their microphones, and not too loud please. Modern in-ear monitoring has solved some of this, but it’s still tricky (and expensive).
- Jyaif 2y agoAnd just like a phased array antenna, by properly spreading the emission of sounds you can change where the speaker is emitting. With proper mixing you could emit different sounds in different directions, at the same time.
- swores 2y agoQuite a few years ago as a teenager, who knew even less about the physics of sound than I do now, assumed that it wouldn't be long before technology was developed that lets a single device (say a consumer TV) output two different audio tracks aimed at two different people, and even track the people moving around the room to keep their audio being directed at their head. Visually the technology for two people to see different video on the same TV has existed for a while, there's just no demand or market for it (either glasses syncing with TV to block certain frames, or there was a technique that depended on the angle you're viewing from). And for tracking people walking around the room, to then know where to point audio or video at, there's released & integrate-able technology available like head and eye tracking from Tobii. Is there also some very expensive option for having audio split between people in the same room (without using any devices like earphones) and just equally no general demand from consumers wanting to use or pay for it, or do the laws of physics prevent sound waves from working well this way?
- BertoldVdb 2y agoI worked on this long ago, the main problem with the poor sound quality is that the self-mixing process is non-linear, a good approximation is squaring the output signal. To improve the quality you can pre-distort the output signal. Taking the square root works quite well, but expands the bandwidth significantly (infinitely, in theory). There is a lot of literature on pre-distortion with bandwidth constraints for telecom power amplifier linearisation. You will also need a linear amplifier to power the array. The ultrasonic transducers used in this post are very narrowband, having a resonance peak of merely a few 100Hz. You can reduce the Q factor with resistive loading but the output power significantly drops. It seemed these transducers quickly start making an audible whining noise when used for continuous transmission at higher powers. I don't know what caused that, apart from this effect they seemed to hold up for essentially infinite duration. Using a larger wideband ultrasonic transducer instead of an array of small narrowband transducers again increases the sound quality a lot. We did not find a commercial supplier of such transducer for a reasonable cost, but made some improvised custom electrostatic ones with conductive foil. There is a lot of literature on how to construct ultrasonic transducers but this is not my field. You will not be able to play bass notes due to physics, the power required would be insane.