3D-printed device splits white noise into an acoustic rainbow without power(phys.org)
phys.org
3D-printed device splits white noise into an acoustic rainbow without power
https://phys.org/news/2025-06-3d-device-white-noise-acoustic.html
64 comments
In the late 80s I worked in a low cluster of buildings, each of which was topped with a band of vertical ridges spaced about 4" apart (sort of like a corrugated roof, but with vertical corrugations). One day a thunderstorm came through, and we discovered that the pulses of thunder, when they hit the corrugations, reflected as a quickly falling tone. The corrugations were working as an acoustic diffraction grating, with different frequencies reflecting in different directions.
I love corregated concrete! Those highly ordered early reflections can make a cool sound if you stand about a few feet away and clap your hands. I've wondered if it was possible to vary the bands to encode a designed sound in the reflection. Probably.
Wait, so you could encode a forrests-leaves-swaying in the wind sound- into corrugated concrete?
Not sure about that, but more like using Impulse Response techniques like in convolution reverb, to craft a short sound that reflects back given a burst of sound like a clap.
For long sustained sounds using evenly space round rods can create sound with wind, like an Aeolean harp.
For long sustained sounds using evenly space round rods can create sound with wind, like an Aeolean harp.
Very neat, this reminds me of the organic shapes of passive demultiplexers in photonics such as https://pubs.acs.org/doi/10.1021/acsphotonics.7b00987
That is a very wild shape indeed. I wonder if there is some analytical way to derive these or if some type of search algorithm will remain the best way.
Given the elegance of the wave equation, I like to imagine there are solutions with some sort of symmetry and structure. We are unfortunately missing the tools and knowledge to find these solutions today!
Thats crazy ! Thanks for sharing
The linked original paper is readable and answered many questions. They simply embrace the idea that some "crazy shape" will work, and then do "machine learning" in a simulation to find it.
It's not really machine learning, it's just optimization (optimize the space of shapes to create the desired filter). The paper doesn't call it ML either
Cool, but I'd rather see a nicer shape, like a human cochlea, which also splits sounds into frequencies.
Perhaps if they added some more constraints (e.g. on smoothness) they would end up with a shape like that.
Perhaps if they added some more constraints (e.g. on smoothness) they would end up with a shape like that.
It seems plausible that Mother Nature had to make some compromises when designing the cochlea, like how much easier it is to grow a (rather symmetric) cochlea than the weird shape from the article and maybe optimizing more for certain sounds than for others.
3d printers and search algorithms don't have that restriction and can directly optimize for optimal splitting and minimal acoustic losses.
3d printers and search algorithms don't have that restriction and can directly optimize for optimal splitting and minimal acoustic losses.
A cochlea doesn't really spatially disperse the frequencies, though, right? Rather, the isolated frequencies are extremely localized within the coil, and the hearing receptors are each located at the one point where they need to be.
This object is sort of an eversion of a cochlea. Perhaps it could be made with a "nice" shape, but I wouldn't assume so.
This object is sort of an eversion of a cochlea. Perhaps it could be made with a "nice" shape, but I wouldn't assume so.
IIRC it is an array of cilia of different sizes that filters sound into different frequencies in the human ear.
What sort of ML method would do shape optimization?
Quite a lot could probably do it. Have it adjust positions/shapes of blocks placed in a virtual setting, have its fitness function be based off how split apart the frequencies are, press train and make a coffee. Sort of like this https://rednuht.org/genetic_cars_2/
Brainstorming applications of knowing your angle relative to a point source:
- adaptive sports for visually impaired players like beep baseball?
- robot swarm members knowing their relative 2d position with a single microphone? (frequency for angle, amplitude for distance)
- a cheap, durable way for human workers to track the rotation cadence of slowly rotating machinery?
- adaptive sports for visually impaired players like beep baseball?
- robot swarm members knowing their relative 2d position with a single microphone? (frequency for angle, amplitude for distance)
- a cheap, durable way for human workers to track the rotation cadence of slowly rotating machinery?
Reminds me of Ben Underwood, the blind kid who used echo location around the house, playing basketball, riding his bike around the neighborhood, etc: https://www.youtube.com/watch?v=fnH7AIwhpik https://en.wikipedia.org/wiki/Human_echolocation#Ben_Underwo...
https://en.wikipedia.org/wiki/Human_echolocation
Bloody hell, I can't do all that...
I wonder how they discovered that "clicking" works, seems so counterintuitive to discover. Though it's fair that I don't spend anywhere near that much time listening carefully and noticing how sharp sounds reflect.
Bloody hell, I can't do all that...
I wonder how they discovered that "clicking" works, seems so counterintuitive to discover. Though it's fair that I don't spend anywhere near that much time listening carefully and noticing how sharp sounds reflect.
> I wonder how they discovered that "clicking" works
I won't think it's they unexpected - have a walk a forest with loud insects. You'll hear a lot of interesting noises shaped a lot by what you stand near to. Large trees especially change how you hear things quite a lot.
I won't think it's they unexpected - have a walk a forest with loud insects. You'll hear a lot of interesting noises shaped a lot by what you stand near to. Large trees especially change how you hear things quite a lot.
Before practical applications, my first thought was a grade-school science fair entry. It’s novel enough for judges not to have seen it for a couple of years.
okay who wants to build a musical instrument that works by beaming white noise at a bunch of these things, with some way for the user to rotate them quickly and accurately
I’m game to do some heavy lifting if you’re serious.
I’m wondering if you can change the shape in such a way that rotating one would produce an arpeggio.
I'm in.
Although I think this also has applications as a mechanical control mechanism, replacing expensive potentiometers with relatively cheaper 3D-printed parts. I've dreamed-up an optical/laser variant in my head a hundred times, fun to look at it in the audio domain.
Although I think this also has applications as a mechanical control mechanism, replacing expensive potentiometers with relatively cheaper 3D-printed parts. I've dreamed-up an optical/laser variant in my head a hundred times, fun to look at it in the audio domain.
Kef has a "metamaterial" they add to their speaker drivers to absorb specific frequencies in order to modify the frequency response curve of the drivers themselves, as opposed to only trying to correct via the cabinet. https://us.kef.com/pages/metamaterial
I can't find it now, but there was a youtube video of a guy building a fence to block road noise by building interlocking pottery 'bricks' with cavities that would absorb certain frequencies
Yes! That’s the one
helmholtz resonators, well known in acoustical engineering, also known as beer bottles and people, enough of which can significantly alter an acoustical signal.
the idea of useing specific shapes to redirect sound is new to me, but parralels how reflected coulor can work in birds and insects, where two mechanisms are employed, pigments that simply absorb(heat up) with some frequencys and reflect others, and then mechanical structures that are tuned to capture some frequencys and reflect others, producing the iridesent effects that are so attractive.
recent work has revealed that silk and artificial cloth's, can convert sound into heat quite effectivly, and other work where transparent plastic is put as an extra sound absorbing layer in windows
Neat method. However, the frequency range for the device is 7600-13600 Hz: less than an octave.
This is the first device of that kind. It's a research paper. The method described works. They weren't going for the limits of the technology here, but proving that it works. Others with different requirements of frequency ranges can create their own versions.
Terrible! I was expecting at least a 7599-13601 Hz split.
This is the kind of thing that keeps me coming back to HN more often than I should. So cool.
I used to think you had to rely on circuits or resonance chambers to split sound frequencies, so seeing this done with a 3D-printed structure really changed how I think about it.
It made me realize how little design attention we actually give to sound. Most of the time we just passively listen, without thinking about shaping the path of sound. If structures like this can be made smaller and more portable, I can see a lot of interesting use cases in phones or compact voice-controlled systems.
It made me realize how little design attention we actually give to sound. Most of the time we just passively listen, without thinking about shaping the path of sound. If structures like this can be made smaller and more portable, I can see a lot of interesting use cases in phones or compact voice-controlled systems.
>Unlike nature, which utilizes passive structures to shape sound, most artificial sound control systems require active devices or resonance-based systems.
What's wrong with resonance-based systems? I have to wonder if their side lobes and frequency range would be better if they used resonance
What's wrong with resonance-based systems? I have to wonder if their side lobes and frequency range would be better if they used resonance
I'd like to passively divert annoying or redundant airport announcements down the drain.
More seriously, great concepts for architects to scale up and control noise?
More seriously, great concepts for architects to scale up and control noise?
Could you build this in to a decoder? A hidden message within the white noise and this filters to one or more frequencies?
Is this similar to how the human ear turns signals into frequencies?
I suppose the thing is linear? So it behaves like a Fourier transform?
I suppose the thing is linear? So it behaves like a Fourier transform?
I think the ear relies more on resonance (unrolled it's like a stretched rubber triangle). The higher you go, the more it reacts on higher frequencies. This one here seems to just use passive reflection to get the effect.
I’m from the future and we use this technique with digitally planted corn seed to build 100000 km^2 diffractive concentrators to more effectively image near the center of the Earth.
How the heck do you arrive at such a crazy shape wow this is amazing.
1. Start with a non-crazy shape that sort of does the same thing but worse (ie non-linearly or with big power fluctuations for different frequencies). Almost all shapes will interact with a sound wave in a frequency dependent manner so you can quickly scan through many initial options.
2. Define a goal function describing the desired outcome (like the "rainbow" shape of the linked article)
3. Permute the shape you started with iteratively with algorithms like simulated annealing, using the goal function from 2 as a means of defining the quality of the current solution.
The actual scientific paper (https://www.science.org/doi/10.1126/sciadv.ads7497) is worth reading. The goal function is the "Figure Of Merit" (FOM), described in equation 1. They also make a two-prong version they call the "lambda emitter" that takes in a mix of sound frequencies and directs low and high-frequency sound waves in different directions.
2. Define a goal function describing the desired outcome (like the "rainbow" shape of the linked article)
3. Permute the shape you started with iteratively with algorithms like simulated annealing, using the goal function from 2 as a means of defining the quality of the current solution.
The actual scientific paper (https://www.science.org/doi/10.1126/sciadv.ads7497) is worth reading. The goal function is the "Figure Of Merit" (FOM), described in equation 1. They also make a two-prong version they call the "lambda emitter" that takes in a mix of sound frequencies and directs low and high-frequency sound waves in different directions.
There are various algorithms for finding approximate optima to messy fitness landscapes.
Genetic algorithm would be one approach. You map the printable shape space onto a bit vector and define a fitness function (optimization objective function) to guide the search. Hardest part is coming up with a fitness function that gives you what you want, this gets tricky when you are trying to balance multiple constraints.
Genetic algorithm would be one approach. You map the printable shape space onto a bit vector and define a fitness function (optimization objective function) to guide the search. Hardest part is coming up with a fitness function that gives you what you want, this gets tricky when you are trying to balance multiple constraints.
Can it be scaled up and done in reverse to create a point source of coherent audio from multiple speaker components covering different frequency ranges?
One more step toward building the pyramids.
I mean we already built the pyramids...
Yeah I'm not sure what the grandparent refers to. They're not mysteries or impossible to build, just labor intensive and expensive. Humanity has built bigger structures since then; skyscrapers, dams, underground complexes like the LHC, stadiums, bridges, cities (non-organically grown), etc.
There are fringe theories that the pyramids were built using sounds to levitate the stone blocks, which are backed up with footage of ultrasonic acoustic levitation of polystyrene balls, and these days probably ai generated video too. Instead of using the Nile to transport them and ramps and rollers to lift them
Whoa it's like an ear but for light!