We’ve seen a number of people create plasma speakers over the years here at Hackaday, so at first blush, the latest Plasma Channel video from [Jay Bowles] might seem like more of the same. Even his overview of the assembly of the 555 timer circuit at the heart of the setup, as detailed as it may be, is something we’ve seen before.
But the back half of the video, where [Jay] talks about the flyback transformer used in this plasma speaker, really got our attention. You see, frustrated by the limited options on the market for AC flybacks, he set out to put together a custom transformer utilizing a 3D printed secondary former of his own design.
Armed with a spare core, [Jay] spent some time in CAD coming up with his secondary. Despite never having built a flyback before, his first attempt managed to produce some impressive sparks — that is, until it arced through the printed plastic and released the critical Magic Smoke. Inspired by this early success, he went back to the digital drawing board and cranked his way through several different iterations until he came up with one that didn’t self-destruct.
High-voltage experimenters have been using automotive ignition coils to generate impressive sparks in the home lab for decades, and why not? They’re cheap, easily obtainable, and at the end of the day, producing sparks is literally what they’re designed to do. But that doesn’t mean there isn’t room for improvement.
In his latest Plasma Channel video [Jay Bowles] revisits this classic experiment, bringing to bear the considerable high-voltage experience he’s gained over the last several years. Building on an earlier setup that used a single Honda ignition coil, this new dual-coil version can produce up to 60,000 volts and is driven by a cleaner and more reliable circuit based on the iconic 555 timer. A pair of potentiometers on the front of the driver can adjust its square wave output from 1 to 10 kilohertz manually, while a commercial Bluetooth audio receiver tied into the 555 circuit allows the output to be modulated by simply playing audio from a paired device.
We’re used to loudspeakers as circular components with a paper cone and a big magnet inside which is suspended a coil that is connected to our audio amplifier. But moving-coil speakers are not the only way to create sound from electricity, there are one or two other weapons in the audio designer’s arsenal.
One of the more spectacular and entertaining is the plasma speaker, and it’s one [Marcin Wachowiak] has been experimenting with. A continuous plasma in the form of a discharge between two electrodes is modulated with an audio signal, and the resulting rapid changes in the volume of plasma creates a sound. The value of a plasma speaker lies in the exceptionally low size and mass of the element producing the sound, meaning that while it can only effectively reproduce high frequencies it can do so from a much closer approximation to a point source than can other types of tweeter. For this reason it’s beloved of some audiophiles, and you will find a few commercially produced plasma tweeters at the high-end of the audio market.
[Marcin] isn’t in it for the audiophilia, instead he’s interested in the properties of the plasma. His plasma speaker does do the job well though, and in particular he’s put a lot of thought into the design of its drive circuit. At its heart is the ubiquitous TL494 PWM controller that you may be more familiar with in the context of switching power supplies, this one applies the audio drive as PWM to the gate of a MOSFET that switches the primary of a flyback transformer. He’s added refinements such as a gate discharge circuit and a second primary winding with a freewheel diode.
The result is an effective plasma speaker. It’s difficult to judge from his YouTube video below the break whether he’s achieved audiophile purity, but happily that’s not the point. We’ve shown you a few other plasma speakers in our time, if the subject interests you then take a look at this rotating plasma vortex, or a version using a 555 timer.
It probably won’t surprise you to know that the US military is very interested in using lasers as weapons. Directed energy weapons such as lasers have many advantages over more traditional kinetic weaponry, not least of which the fact that you don’t need to cart around ammunition for them. But somewhat surprisingly, some of the most promising laser developments have been in the field of non-lethal weaponry. While the mental image of a laser is usually a destructive one, recent demonstrations by the Joint Non-Lethal Weapons Program show lasers can do more than blow holes your target.
As reported by [Patrick Tucker] of Defense One, a radical new laser-powered sonic weapon was shown off at the “Directed Energy to DC Exhibition”. The system uses two lasers: one to generate a ball of plasma when it hits the target, and another to modulate the plasma ball in open air. The result is a variation of the classic plasma speaker demonstration, where plasma is used as a a driver for a massless speaker.
Currently the system is capable of generating a deafening crack at the target area, with a measured intensity as high as 140 dB. That’s about as loud as fireworks or a shotgun going off at close distance, and in theory is enough to drive off whoever is unlucky enough to be targeted with the beam.
In time, the researchers hope to refine their secondary modulation laser to the point that they can play audio over the plasma. This would allow the beam to be used as a directed loud speaker of sorts, which could prove useful for defensive applications. Only the target would be able to hear the audio, which could be a recording telling them they were entering a secured area. A disembodied voice telling you to turn around sounds like a extremely effective non-violent deterrent to us. The voices in our head don’t have to tell us twice.
We recently looked at the possibility of targeted sonic weapons being used in Cuba, and of course, we’ve covered many plasma speakers on Hackaday over the years. Plasma speakers have always been more or less nothing more than a fun high voltage demonstration, so to see them potentially weaponized is a crossover episode we weren’t expecting.
[Anthony Garofalo] has made a fancier plasma speaker. Not content with a simple spark, he uses a plasma vortex. To make the vortex, the spark gap is swapped out for an electrode placed in the centre of a ring magnet. The Lorentz force experienced by the arc causes it to rotate rapidly enough round the arc of the magnet’s centre to appear as a continuous sheet of plasma.
The speaker gets its power from an inverter using a flyback transformer driven through a MOSFET by a 555-based pulse width modulator. You can see the result in the video below the break, it’s very impressive to look at but probably not quite ready to sit in your hi-fi stack. The resulting sound isn’t quite as good as that from a stationary arc, but it looks a lot cooler.
The 555 can do anything. OK, that’s become a bit of a trope in our community, but there is quite a lot of truth behind it: this little timer chip is an astonishingly versatile component.
[Alexander Lang] has added another achievement to the 555’s repertoire, he’s used one in the creation of a plasma speaker. Working at Hackspace Manchester, he’s used the 555 as a pulse-width modulator that drives a flyback transformer through a MOSFET, which feeds a spark gap mounted in a lasercut enclosure. The results maybe aren’t yet hi-fi, but it works, and is very audible.
We’ve been following this project for a while, as he’s updated his progress through several iterations. From initial design idea through PCB and enclosure design, to a first working prototype and some audio refinements, and finally this latest post with the spark gap in its enclosure. He is still refining his speaker, so there is more to come
In the video below the break he demonstrates his pulse width modulator, and tests the device using a keyboard as an input.