TOSLINK was developed in the early 1980s as a simple interface for sending digital audio over fiber optic cables, and despite its age, is still featured on plenty of modern home entertainment devices. As demonstrated by [DIY Perks], this old tech can even be taught some new tricks — namely, transmitting surround sound wirelessly.
Often, a TOSLINK stream is transmitted with a simple LED. [DIY Perks] realized that the TOSLINK signal could instead be used to modulate a cheap red laser diode. This would allow the audio signal to be sent wirelessly through the open air for quite some distance, assuming you could accurately aim it at a TOSLINK receiver. The first test was successful, with the aid of a nifty trick, [DIY Perks] filled the open TOSLINK port with a translucent plastic diffuser to make a larger target to aim at.
The rest of the video demonstrates how this technique can be used for surround sound transmission without cables. [DIY Perks] whipped up a series of 3D printed ceiling mirror mounts that could tidily bounce laser light for each surround channel to each individual satellite speaker.
It’s a very innovative way to do surround sound. It’s not a complete solution to wiring issues—you still need a way to power each speaker. Ultimately, though, it’s a super cool way to run your home theater setup that will surely be a talking point when your guests notice the laser mirrors on the ceiling.
We’ve seen some other stealthy surround sound setups before, too.
[Thanks to jenningsthecat for the tip!]
Hope that pretty lights it won’t atract JDAMs.
And why you didn’t mention the hobbit house where you can use those speakers?
9 months old video…
Hello!
I know but I choosed to make fun instead of compaining (just saying, not complaining about your complaining). Also did you get the answer to my question? Hint: read again the first paragraph. ;)
One downside of long transmission line speakers: building up the resonance to get the sound pressure takes time, which creates lag, which is the very thing that he’s trying to avoid, and it kills the transient response (e.g. drum hits).
It’s great for those movie effects with a long bellowing bass, because you don’t care whether the constant droning comes 300 ms late, but for listening to music it’s just going to muddle it completely.
Also, killing the resonance takes time, so when the speaker stops vibrating the entire tube is still ringing with the sound for tens of cycles before the sound goes away. You could mitigate that effect by adding dampers, but then the resonance won’t build up as strongly and the bass becomes muted.
In other words, making a tiny driver sound big by adding a huge resonating volume to it is a gimmick.
For the sound to reach the speakers with a 300ms delay, the source had to be around a hundred thousand km away…
You will need a pretty powerful laser, and play from (or to) somewhere in space. A third of the distance to the moon, give or take.
Elon’s working on it.
That was in terms of the resonance. At 30 Hz one cycle takes 33 ms and if it takes 10 cycles to build up the resonance, then the sound pressure is going to reach peak 330 ms later.
And consider, one stomp of a bass drum decays in couple cycles, so it’s not long enough to build much of a resonance in the tube, but for what it does, the sound keeps vibrating for much longer than the actual drum hit.
What you’re getting is essentially this (Blue Man Group):
https://youtu.be/zHcM7H44XCw?t=41
Note how long it takes for the note to actually change when one of the guys suddenly extends the tube. The video might be out of sync, but that’s not inconsistent with the physics of it.
Though sound travels at 340 m/s so technically just 102 m away would be consistent for 300 ms.
So the effect is like a big stadium. The mid and high range speakers are right in front of you, and the subwoofer, at least in terms of peak sound pressure, is a football field away from you.
Theyre talking about the speaker box resonance, not the laser transmission system.
haha you shoulda summarized the video for us before telling this comment, because Lewin Day failed to do that, and most of us who read the comments don’t watch the videos :)
i had no idea the attached video was about a novel cabinet design, so i thought you were way off topic at first
I thought the video was actually about selling ratcheting screwdrivers.
The rest of it is just faffing about with gimmicky means of transmitting audio and building speakers. As if there’s no delay or error, or general loss of fidelity in those multiple chained DA/AD/DA/AD/DA conversions involving the converters, transmitters, and DSPs the guy puts in.
I think you missed a few conversions.
HDMI to analog: DA
DSP in: AD
DSP out: DA
SPDIF transmitter: AD
SPDIF receiver: DA
DSP in: AD
DSP out: DA
and if this is a class D amplifier: AD
Forget what I said. It doesn’t make sense for the DSP in the center speaker to process the signals for the other speakers.
Also note how he puts effort into explaining and mitigating the “comb-filter” problem of the middle speaker, where you get destructive interference from multiple speaker cones placed in line horizontally, so listeners who are not on the center line of the speaker will get different frequency responses out of the setup.
So, he puts the tweeter and the mid cone in-line on top of one another. Problem solved – except, he then mounts the speaker high up above the TV so the constructive and destructive interference problem re-appears for listeners who are at different heights and distances from the TV, because now the same issue is simply shifted to the vertical plane. If you want to lay down on the couch instead of sitting up, the sound is going to be different.
Selling the setup as something better is forgetting the important factor: there’s no perfect solution to sound systems – it’s all a bunch of compromises and you have to pick what you can live with.
When I was still obsessed about these sort of things, I made a simulation of my 5.1 desk setup, by plotting where each speaker was. I then placed a grayscale ripple pattern on top of each speaker and added them together to find where the interference pattern would land at 1 kHz. Turns out, shifting my head by just a foot would completely change the outcome, which was confirmed by me dancing like an Egyptian around the desk. The outcome: I learned to stop worrying and love the bomb.
To understand resonance, consider: the tube does not actually increase the power of the speaker. It collects the energy you put in and returns it back with a delay, so it can give you a higher peak pressure.
It is like an underdamped LR low-pass filter (see the second graph)
https://math.stackexchange.com/questions/1791259/how-to-differentiate-step-responses-of-1st-order-and-2nd-order-systems
So the resonant tube initially makes the sound quieter by absorbing the energy that would otherwise come out of the speaker, but then later, it adds it back to the energy that the speaker is putting out. This is not a permanent effect – if the speaker keeps working at a constant power, the output pressure will eventually stabilize to match that power.
This creates the illusion that the speaker is louder, but only for certain cases. A pulse of sound that is too short will be damped by the resonant tube, and a pulse that is too long will eventually return to its true level. In both cases, since the overall effect is a low-pass filter, the peak volume of the pulse of sound will be delayed.
And curiously enough, especially for human speech, the frequency of the sound is not the important factor: most of the information is encoded in the relative phase delays. I can’t find the research paper right now, but I remember an experiment where they scrambled the frequency contents of speech but kept the phase of sound at each original frequency band intact – and the modified speech was completely intelligible. The other way around, not so much.
What that means is, if you’re listening to a person with a low voice through a sound system with heavy delays in the bass ranges, their speech becomes roughly “wubbubbub ububbubbub hubub dubub wodubbubbub”. I’m sure many people recognize the effect.
The bandwidth still matters, though.
Children and female voices have the information encoded in the upper part of the human voice spectrum.
That’s why SSB on the amateur radio bands is a little bit sexist, also.
Because back innthe 1960s it was chosen to suit old men in suits with a tie, rather than everyone.
The typical bandwidth limit of ca. 3 KHz might be fine for old male voices (the primary democratic btw),
but it’s not ideal for young voices (including young men and teenage boys).
That’s why low-pass filtering on shortwave reception only works so far.
It removes hisses and noise and makes things sound “smoother” to the ear, but it will also make sound everything dull.
For old male voices, that might be still okay, since the brain also reconstructs missing information. It’s not an ideal solution, though.
“Allowing” a bit more bandwidth (say 6 KHz as with AM in the old days) to also include young amateurs and females and to improve overall quality would be just fair.
More information on Extended SSB:
https://www.nu9n.com/intro.html
https://www.essb.us/what_is_essb.html
2 points though. First a true TL speaker isn’t resonant, it’s just (ideally) a delay line with the line length set to 1/4 of the lowest frequency, giving it a 90deg phase shift wrt the wavefront from the front of the speaker. As the frequency increases the fixed line length imparts a greater phase shift. When it’s a full half wavelength the output at the TL end is inphase, though delayed 1 cycle, with the “front wave”. And that’s where the peak frequency response should be. So there’s no 10 cycle delay. Ideally.
Second, I don’t know what to call his subwoofer. A TL has all sorts of absorbing material to remove the resonances that would also occur at the 2nd, 3rd… harmonics. I didn’t see any used in his video and if that’s true, it’ll color the sound pretty noticably. He may call it a TL design but if it’s one, it’s a pretty poor one. It will be more of a pipe organ, with a Q that I don’t know.
Precisely. That’s also why I used the Blue Man Group as an example – every bass hit is like playing their PVC pipe organ.
Which may be the point, because that can lead to a psychoacoustic effect where the missing bass note is “heard” from the harmonic series even when the actual note is missing. This is used in audio engineering to make cellphones and laptops etc. sound like they have “bass” even when they really don’t.
https://en.wikipedia.org/wiki/Missing_fundamental
So this might be a case of lucky cargo cult engineering: the guy thinks he’s making a transmission line speaker, but actually ends up making a resonant tube that creates a psychoacoustic effect that makes the bass “better” by a trick of the brain. Or, he might just be saying so and actually the speakers sound like crap.
RE: Dude – all excellent points brought forth.
Spoiler – in the past I’ve assisted with setting up, tuning and running stage equipment, obviously, back then it was all analog, mixers, amps, speakers, etc etc. All those things are learned bit by bit, by doing, and reading some literature, and doing again.
One of the challenges was always things like kick drum mikes clipping themselves at unexpected frequencies, while the booming sound, delayed, travels through the singers’ mikes, freshly combed and re-amplified, gets sent right back through the sides of the stage speakers – to resonate with the snare drum’s strings : – ] That always sounded creepy, though not unexpected, among other sudden feedbacks of unclear origins (monitor speakers beneath singers … sure they are aimed at the ceiling, and out of phase, but the cone bleeds from these usually radiate everywhere … like, try guitar amps’ reverb springs that rattle a little … the smaller the stage, the worst it gets, the stage itself, too, always has few resonant frequencies that occasionally get triggered … like, during backing dancers stomping at the wrong time/place, or some kind of loud choir singing in sudden/perfect unison the same note : – ])
IMHO, Large haul acoustics and one third science, one third art, and one third witchcraft. Large haul acoustics with shifting resonators/dampers (dancers … wandering spectators … etc) – even more so, and things like dancing hauls with marble floors and bare walls are the thing (the hall is quarter full … of half full … or packed … ceiling may factor in, too, if it is relatively low … chandeliers are known to deflect some sounds quite well, if they are sufficiently large and hang low … and tabletops, if not covered with tablecloths, too).
Then, of course, there is magic with placing of the speakers, inline, out of phase, same height, etc. I’ve also helped with the traveling shows set up places not built for anything louder than a small choir accompanied by upright piano (schools’ mess halls).
Fun times.
Could I use an IR laser diode for this setup, so my place doesn’t look like a disco?
If you’re running a fog machine constantly, it’s going to look like a disco regardless. Also, IR lasers are going to be much harder to align.
Perhaps you could replace the transmitter with a big IR diode and put an IR photodiode in the receiver, so you can just bounce the light off the ceiling like normal remotes do.
The S/PDIF signal can contain compressed 5.1 audio, so each receiver can get an identical copy and just pick whichever channel they need.
And many people have done so. Even if you need mirrors to aim the thing, the placement of the receiver becomes less critical with the wider cone of light.
https://www.jensign.com/SPDIFLink/
In the 90’s I had some wireless Beyerdynamic headphones. The transmitter simply flooded the room with almost-IR LEDs. But if I remember correctly it modulated the analog signals instead of going digital. You could see the LEDs getting brighter with loud sounds.
That’s a cool idea, but there are way too many analog to digital and digital to analog conversions. That’s going to reduce the audio quality and add a lot of latency. A lot of those conversions could be eliminated, but probably not with off the shelf hardware.
I’m surprised it worked at all. I wonder if the TOSLINK receivers have an AGC circuit? I would have expected ambient light to cause reception issues.
Nah, it’s just a photodiode with a buffer amp and a high pass filter to remove the DC offset. It relies on the fact that it’s hard to get enough light into the diode to actually saturate it. Pretty much similar to IR remotes.
Flickering ambient lights, like a strobing LED lamp nearby would cause issues because the 100/120 Hz blinking will pass through the filter. There’s nothing to guard against that, since it’s supposed to be connected by optical fiber so nothing else gets in.