Directional speakers - Page 1
Forum section: electronics / projects

author: moffy
author_rank: Super Contributor
timestamp: January 13, 2025, 01:16:20 am
content: Saw this video where an array of ultrasonic transducers are modulated with an audio signal and it ends up as a directional audio speaker. I expect the distortion would be terrible, but it is an interesting concept.

author: Marco
author_rank: Super Contributor
timestamp: January 13, 2025, 01:31:09 am
content: Are you sure this is a directional audio speaker and not a directional ultrasonic speaker? Usually it's the high frequency modulated signal being down-mixed which creates audio.Wonder if the commercial versions use higher frequency transducers, so they don't have to swing so much from their resonant frequency. You can probably find some data in patents, or maybe the audio engineering society journal.

author: moffy
author_rank: Super Contributor
timestamp: January 13, 2025, 02:02:41 am
content: Quote from: moffy on January 13, 2025, 01:16:20 amQuote from: Marco on January 13, 2025, 01:31:09 amNot sure of the distinction you are trying to make, as mentioned the ultrasonic signal, the 40kHz carrier is modulated with the audio signal, and appears to the listener as directional audio.

author: ledtester
author_rank: Super Contributor
timestamp: January 13, 2025, 02:52:16 am
content: You might also want to check out the SonicSurface:https://hackaday.com/2021/08/18/phased-array-levitation-is-science-in-action/https://youtu.be/vAEZvYlUnEMwhich is a 256 element ultrasonic array using an FPGA to individually control each transducer.(There is also an earlier version of the project utilizing 64 transducers under the control of an Arduino Mega:https://youtu.be/h0Mh0bIv9Fk)A main feature of this project is the PC software, Ultraino, which helps you create custom acoustic fields - for example levitation choreographies involving multiple points.You can see the software in action here:https://youtu.be/vAEZvYlUnEM?t=8m47sIt also can be used as a directional speaker with directionality controlled via software:https://youtu.be/h0Mh0bIv9Fk&t=10m53s

author: moffy
author_rank: Super Contributor
timestamp: January 13, 2025, 03:05:17 am
content: I certainly will have a look at the links.P.S.has a nice simple explanation of the physical principles involved, as well as a simple test circuit.

author: ajb
author_rank: Super Contributor
timestamp: January 13, 2025, 04:33:29 am
content: A friend had a commercially-made speaker like this, it was a lot of fun to play with. You really can 'bounce' sound quite effectively around a room with it like in the video moffy linked,At a much larger scale, there's a commercial system based on arrays of 1.3", 5", and 18" transducers:https://holoplot.com/products/systems/x1/At those sizes, they're not relying on ultrasonic conversion, but a ton of DSP to sculpt the wavefront at the array to create the desired wavefront at the listening position. According to the documentation on their website, they can even construct sound sources at a point in space between the array and the audience by creating a converging wavefront. Kind of like focusing light with a magnifying glass, at points beyond the focal plane, the light seems to emanate from a point source at the focus, except instead of a lens it's a really complicated phased array.https://docs.holoplot.com/introduction-to-holoplot/holoplot-technology#wave-field-synthesis

author: moffy
author_rank: Super Contributor
timestamp: January 13, 2025, 05:12:41 am
content: Quote from: ajb on January 13, 2025, 04:33:29 amDo you remember what the sound quality was like? It is hard to judge from the videos as the microphones, understandably, have trouble capturing the audio.

author: ajb
author_rank: Super Contributor
timestamp: January 13, 2025, 03:46:17 pm
content: Quote from: moffy on January 13, 2025, 05:12:41 amFrom memory, it wasn't too bad, but a bit on the tinny side. The quality of reflected sound depended somewhat on the reflecting surface as well, which is to be expected. Not hifi by any means, but certainly listenable.

author: ledtester
author_rank: Super Contributor
timestamp: January 14, 2025, 08:08:15 am
content: Another cool project:A Volumetric Display using an Acoustically Trapped Particle -- Dan Foisyhttps://youtu.be/hCC1C5KIeUAProject files:https://github.com/danfoisy/vdatp

author: Andy Chee
author_rank: Super Contributor
timestamp: January 14, 2025, 08:30:46 am
content: Mark Rober used an ultrasonic speaker in a Halloween prank (scroll to 6:35 for the brief technical details, 13:30 for the prank)

author: Analog Kid
author_rank: Super Contributor
timestamp: January 14, 2025, 08:42:07 am
content: Ah, the porch-pirate punisher guy. Farts in a can and all that.

author: tszaboo
author_rank: Super Contributor
timestamp: January 14, 2025, 12:07:05 pm
content: Quote from: Marco on January 13, 2025, 01:31:09 amWhat's actually demodulating the signal? I get the part that ie. a piece of cardboard would do it, but I'm just wondering how does an AM modulated ultrasonic signal turn into demodulated sound.

author: jrs45
author_rank: Regular Contributor
timestamp: January 14, 2025, 02:55:47 pm
content: The air demodulates the signal, surprisingly!

author: moffy
author_rank: Super Contributor
timestamp: January 14, 2025, 10:02:20 pm
content: Quote from: tszaboo on January 14, 2025, 12:07:05 pmMy brief understanding is that when the air contacts a surface it acts in a non linear fashion to demodulate the signal, have a look at post#5 the video links a paper.