The world of audio has produced a variety of different loudspeaker designs over the last century, though it’s fair to say that the trusty moving coil reigns supreme. That hasn’t stopped plenty of engineers from trying new ways to make sound though, and [R.U.H] is here with a home-made version of one of them. It’s a foil tweeter, a design in which a corrugated strip of foil is held in a magnetic field, and vibrates when an audio frequency current is passed through it.
He shows a couple of takes on the design, both with neodymium magnets but with different foils and 3D printed or wooden surrounds. They both make a noise when plugged into an amplifier, and unsurprisingly the thicker foil has less of the high notes.
We can see that in there is the possibility for a high quality tweeter, but we can’t help having one concern. This device has an extremely low impedance compared to the amplifier, and thus would probably be drawing far too much current. We’d expect it to be driven through a transformer instead, if he had any care for not killing the amplifier.
Happily there are other uses for a ribbon, they are far better known as microphones.
Metallized mylar from a balloon might work better.
As far as the resistance goes, putting an 8 ohm resistor in series might help.
… and would reduce the output by A LOT. This is a copycat version of the Heil Air Motion Transformer.
True but it would help reduce the risk of amplifier damage until a better solution is found or during early testing/prototyping.
It looks like an Air Motion Transformer but it’s not acting in the same way. In an AMT, the conductive trace travels in opposite directions on each side of each pleat. This causes the pleats to open and close in response to positive and negative current, effectively squeezing air out from between the pleats.
This is acting more like a planar magnetic driver with the whole membrane moving back and forth.
That is exactly what I was thinking. Of course, I did envision the addition of a flux capacitor and a qubit collector.
Magnepan have been making foil ribbon tweeters for decades, and they sound fantastic.
https://www.magneplanar.com/about
Love the background tweeter ….and rooster :-)
Old tech. There was normally a high voltage / low current amp or transformer to run these.
This might be my favorite HaD article of 2024. So minimal, interesting, and functional. Anyone could experiment with this and get o vious results without a lot of tools. Awesome!
At 11:10 the subs says “because its true role is not bass but low frequencies”
My understanding is it should have been “because its true role is not bass but HIGH frequencies” (otherwise I did not get it)
Apart of that great build and video
Edit :
At 11:10 the subs say “because its true role is not bass but low frequencies”
My understanding is it should have been “because its true role is not bass but HIGH frequencies” (otherwise I do not get it)
Apart of that great build and video
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A tweeter is normally connected to a crossover network that keeps low frequency energy away from the delicate conductors in the driver, making it safer for both the amp and the tweeter. In this case, the conductor isn’t so delicate, and the amp in the cheesy record player probably doesn’t have enough juice to destroy itself, let alone burn through a near dead short with a thick piece of aluminum foil, but I’d hesitate to hook this thing to a good amplifier.
A Heil AMT has a conductor that snakes up and down a polyester film that is then folded at each pass of the conductor. The longer, narrower conductive path is higher resistance, so the amp is a little happier, and as it operates the folds open and close a bit “squirting” the air from between them.
As built, this thing just vibrates. In real ribbon tweeters, corrugations are used to minimize or raise the resonances frequencies in the driver.
Yes, not an a Heil, I have a pair. Watching only 2 minutes of the video I see the magnets seem to be N S end to end and the depositing of the sequence of magnets seem to make the strip alternate and when the 2 sides meet they’re off by a magnet’s size instead of inseparable and aligned. There should be nothing but N on one side and S on the other side and keeping them apart is a herculean task not for popsicle sticks.
If you took these magnets shown and stacked them ‘the right way under control they would have one big field and would want to fly apart. So the ribbon here has alternating sections out of phase with itself? Most of the flux goes right to the adjacent magnet.
Magnetic iron is most of the mass in the Heil tweeter besides 2 ceramic magnets. Today neodymium magnets would not shrink the size much of all that needed iron. It’s all about one even field of concentrated flux across a gap where the ribbon resides. Pleats alternating or or single ribbon the field is the same.
This is not new and if we are to believe the marketing it’s currently in its most sucessful implementation by the Danish loudspeaker company Raidho. They brag with the lightest foil ever made for such a tweeter. I listened to 2 of their speakers and the tweeters are exceptionally clear sounding wihout the slightest harshness. I’d they the technology is promising :))