[HN Gopher] Making a rickroll laser: A parametric speaker
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Making a rickroll laser: A parametric speaker
Author : pabs3
Score : 116 points
Date : 2024-09-14 14:59 UTC (8 hours ago)
(HTM) web link (10maurycy10.github.io)
(TXT) w3m dump (10maurycy10.github.io)
| slicktux wrote:
| Pretty 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 wrote:
| Fwiw lrad is regular speakers. Not ultrasound. Just tweeters.
| jamal-kumar wrote:
| Those 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 wrote:
| Is this dangerous in terms of hearing damage due to the perceived
| low sound level alongside inaudible louder ultrasound?
| RadiozRadioz wrote:
| This 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.
| nihzm wrote:
| I 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 wrote:
| I was thinking about how the air itself must be contributing
| to the construction of the (standing?) sound wave as a
| resonator.
| nihzm wrote:
| Not 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...
| nothacking_ wrote:
| I'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 wrote:
| No, 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 wrote:
| Awesome - very cool project!
| tomcam wrote:
| The 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 wrote:
| Surely waterproof headphones would be far easier and sound far
| better
| tomcam wrote:
| You 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.
| dylan604 wrote:
| They 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 wrote:
| so, basically, beamforming but for sound ?
| graycat wrote:
| Lasers? 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 wrote:
| So 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 wrote:
| As far as I understand yes, I would also guess that it is
| analogous to a phased array antenna, but with sound waves
| jamal-kumar wrote:
| It'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/Sound_amplification_by_stimula...
|
| https://www.youtube.com/watch?v=aBdVfUnS-pM
|
| https://en.wikipedia.org/wiki/Sound_from_ultrasound
| aidenn0 wrote:
| This 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 wrote:
| What'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.instructables.com/Acoustic-Levitator/
|
| https://pubs.aip.org/aip/rsi/article/88/8/085105/962938/Tiny...
|
| 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
| klysm wrote:
| The novelty fog fountains are typically a piezo micro mesh with
| tiny holes, which is similar but distinct from ultrasonic
| atomization
| dylan604 wrote:
| "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
| 180deg and pretty much scatter up reflection?
| TeMPOraL wrote:
| That 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 wrote:
| some 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_ wrote:
| With 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. So 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
| sphere). 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 sphere).
| Now push it up against a wall: quarter sphere. And finally,
| put it in the corner of the room: eighth sphere. 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 and acoustically transparent.
|
| The next time you are deciding where to position your
| bluetooth speaker, if it's lacking in bass, boundary-load it.
| jonway wrote:
| I 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.
| andoando wrote:
| Should put these random places in the streets and have them play
| at random times
| Lammy wrote:
| The security state decrees that this is not a good idea
| https://en.wikipedia.org/wiki/2007_Boston_Mooninite_panic
| joezydeco wrote:
| I want a compact version I can point out a car window at the
| glass of another car and turn it into a voice speaker.
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