Could aluminum foil (like cooking foil) be used as a transducer? I mean since most ribbons and magneplanars use aluminum strips attached to a mylar or similar membrane. So could use just forgo the mylar and use the foil since the entire surface is aluminum. Although you wouldn't be able to stretch it like mylar thats for sure.
Anyways any ideas on this. Oh ya one question, a fundamental one I suppose. Since aluminum isn't magnetic, how do ribbons and stuff work exactly? Does the electromagnet affect aluminum differently than a earth magnet?
Anyways any ideas on this. Oh ya one question, a fundamental one I suppose. Since aluminum isn't magnetic, how do ribbons and stuff work exactly? Does the electromagnet affect aluminum differently than a earth magnet?
The simple answer is yes it can. It is available in various
thicknesses, obviously usually the thinner the better.
Aluminium is a non-magnetic conductor similar to copper.
Copper is a a good conductor, but conductance/weight aluminium
wins out. So Aluminium is used in speaker voice coils when light
weight is required and is the general choice of conductor for
panel and ribbon drivers.
Even with a stepdown transformer working at low resistances
can be a nightmare due to contact resistances . So commonly
the foil is slitted and mylar or similar backing added.
Either to create a higher resistance diaphragm and / or to
control the current directions in a magneplanar type driver.
sreten.
thicknesses, obviously usually the thinner the better.
Aluminium is a non-magnetic conductor similar to copper.
Copper is a a good conductor, but conductance/weight aluminium
wins out. So Aluminium is used in speaker voice coils when light
weight is required and is the general choice of conductor for
panel and ribbon drivers.
Even with a stepdown transformer working at low resistances
can be a nightmare due to contact resistances . So commonly
the foil is slitted and mylar or similar backing added.
Either to create a higher resistance diaphragm and / or to
control the current directions in a magneplanar type driver.
sreten.What's less known is that aluminium has much worse mechanical yield and fatigue properties than copper. As well as that, to get the same conductivity with aluminium as with copper, the aluminium foil has to be much thicker and that compounds the problem.
Whatever the material, the conductivity has to be good because the amount of current flowing through the magnetic field is a major factor that determines how loud the speaker's gonna be. And the magnetic gap is extremely wide and often requires massive neodymium magnets. Because of the super-low resistance of those solid metal ribbons they generally have big transformers hanging off the back so you can operate them with ordinary amplifiers.
CM
Whatever the material, the conductivity has to be good because the amount of current flowing through the magnetic field is a major factor that determines how loud the speaker's gonna be. And the magnetic gap is extremely wide and often requires massive neodymium magnets. Because of the super-low resistance of those solid metal ribbons they generally have big transformers hanging off the back so you can operate them with ordinary amplifiers.
CM
Yes, aluminum foil can be used as a membrane. Your problem will be getting enough resistance. Ordinary kitchen foil is too thick and too wide. Narrower and thinner is the ticket. You'll need to think in terms of a transformer if you can't get the resistance up high enough.
You'll need strong magnets and they'll need to be close together so that the flux lines are reasonably straight, otherwise you'll get high distortion from the driver itself. It also increases the field strength, making the driver more efficient. Having the magnets close together goes hand in hand with having a narrow tweeter element, but doesn't work too well for midranges and very poorly for woofers. This is why you keep hearing about ribbon tweeters, but not ribbon subwoofers.
In the Magneplanar ribbon tweeter there is no Mylar or other plastic, just the aluminum. The aluminum is run through a machine that crimps it so that the actual element has tiny ridges in it; they run across the element, not down the length.
Other drivers do use various plastic backings.
True, aluminum isn't magnetic, but it doesn't need to be for the same reason that copper voice coil wires don't need to be. The driving force comes from the magnetic field created by the audio signal. This interacts with the fixed magnets' field to move the ribbon. In fact, using a ferro-magnetic wire (or ribbon elements) would create distortion, since the wire would magnetize and hold the field through hysteresis, giving the signal a hangover effect.
For what it's worth, I have made drivers out of the aluminized plastic from an old Wondercap. Yes it worked. It wasn't very efficient, but then I was using a relatively wide element (about an inch, as I recall). The aluminum coating is very thin indeed and has a fairly high resistance.
Oddly enough, one of your biggest problems will be getting the signal into the aluminum. The easiest method is to clamp something to the aluminum. It's not as though you can solder it and by the time it gets thin enough to do you any good, it's really, really delicate.
Grey
You'll need strong magnets and they'll need to be close together so that the flux lines are reasonably straight, otherwise you'll get high distortion from the driver itself. It also increases the field strength, making the driver more efficient. Having the magnets close together goes hand in hand with having a narrow tweeter element, but doesn't work too well for midranges and very poorly for woofers. This is why you keep hearing about ribbon tweeters, but not ribbon subwoofers.
In the Magneplanar ribbon tweeter there is no Mylar or other plastic, just the aluminum. The aluminum is run through a machine that crimps it so that the actual element has tiny ridges in it; they run across the element, not down the length.
Other drivers do use various plastic backings.
True, aluminum isn't magnetic, but it doesn't need to be for the same reason that copper voice coil wires don't need to be. The driving force comes from the magnetic field created by the audio signal. This interacts with the fixed magnets' field to move the ribbon. In fact, using a ferro-magnetic wire (or ribbon elements) would create distortion, since the wire would magnetize and hold the field through hysteresis, giving the signal a hangover effect.
For what it's worth, I have made drivers out of the aluminized plastic from an old Wondercap. Yes it worked. It wasn't very efficient, but then I was using a relatively wide element (about an inch, as I recall). The aluminum coating is very thin indeed and has a fairly high resistance.
Oddly enough, one of your biggest problems will be getting the signal into the aluminum. The easiest method is to clamp something to the aluminum. It's not as though you can solder it and by the time it gets thin enough to do you any good, it's really, really delicate.
Grey
You may want to experiment with using a transformer from a soldering iron (one of the ones that have a U-shaped wire for the tip), but I don't know if the result would be any good as it's designed for 50-60Hz. You could try etching away at the foil with caustic soda or something like that to make it thinner. Alternatively, look for some techniques used for DIY electrostatics: such as graphite powder pressed into soft plastic foil or similar, or electroplating. How about a conductive spray or antistatic spray?
If you have a look at some commercial ribbon tweeters, you'll see that most of them have bulky transformers that are huge compared to the neodymium magnets that they use. If you go in the other direction for extreeeeeemmmeeely thin foil, you might have consistency problems and might never get a matched stereo pair.
CM
If you have a look at some commercial ribbon tweeters, you'll see that most of them have bulky transformers that are huge compared to the neodymium magnets that they use. If you go in the other direction for extreeeeeemmmeeely thin foil, you might have consistency problems and might never get a matched stereo pair.
CM
Hybrid fourdoor said:
Yes, but it's right - resistance would'nt get low enough, unless you split up the surface to a number of long small strips and connect in serial configuration - like in the tweeter you see on my apogee-clone:http://www.diyaudio.com/forums/showthread.php?s=&threadid=23208&perpage=15&pagenumber=19
Hi,
In the "Loudspeaker and Headphone Handbook" by John Borwick there is a very good description how ribbon speakers work complete with the math. There is also an investigation about what the most efficient conductor for the ribbon is. Aluminium has simply the best conductivity – weight balance of all metals for use as a ribbon.
Overheating is the biggest enemy of ribbons, they simply melt when severe overloaded. But too much low frequency content will damage the ribbon as well by irreversible stretching it. Therefore don’t use 1st order x-overs with ribbon tweeters unless the frequency is quite high ( > 5 kHz).
Cheers
In the "Loudspeaker and Headphone Handbook" by John Borwick there is a very good description how ribbon speakers work complete with the math. There is also an investigation about what the most efficient conductor for the ribbon is. Aluminium has simply the best conductivity – weight balance of all metals for use as a ribbon.
Overheating is the biggest enemy of ribbons, they simply melt when severe overloaded. But too much low frequency content will damage the ribbon as well by irreversible stretching it. Therefore don’t use 1st order x-overs with ribbon tweeters unless the frequency is quite high ( > 5 kHz).
Cheers
Pjotr said:
My "La Folia" (apogee-clones) consists of a large low-frequence panel and a long ribbon (7 serial aluminium tapes - each about 1m long and 5 mm wide - taped to a common pvc-ribbon. My cross-over is FIRST-ORDER 1kHz and I have often played with full power from my earlier power-amps. Above 1kHz often about 80W into 3 ohm - no problem and no overheating.
Only once, when my wife came to close with the vacumcleaner, the ribbon was damaged
, and I had to corrugate it once again.
I've had great results using a ferrite transformer from a 200W PC switchmode PSU. Contrary to popular belief, they work fine above 2kHz (contributing <0.1% distortion in open loop, even with >10W of power).
Use only one half of the secondary to get a ~12:1 ratio. This gives ~ 144:1 impedance transformation. My ribbons use cheap kitchen alfoil. Cheaper brands are thinner, and have less hardening (which is what you want). Initially, I used cam gears from a car engine to crinkle, but the corrugations were too big (and deep) resulting in the ribbon being too sloppy. I've found some rubber floor grip with 1mm grooves which works great for corrugating.
The thick-foil ribbons work fine until you get to 20mm, then the stiffness of the foil starts to cause some nasty resonances in the horizontal. I tamed mine with a very thin PVA coating. Thinner foil would really help here.
So technically they aren't true ribbons any more...
Soon I will have the transformer inside the feedback loop of the amplifier (like most decent valve amps).
If you dont mind super-directional sound in the vertical axis(makes it sound like you have no ceiling), ribbons offer an amazing amount of detail. The transient response is simply superb.
Oh yeah- and dont bother unless you buy some neo magnets. Check out John Whittaker's site:
http://www.snippets.org/alsr/index.php3#SIZE
Chris
Use only one half of the secondary to get a ~12:1 ratio. This gives ~ 144:1 impedance transformation. My ribbons use cheap kitchen alfoil. Cheaper brands are thinner, and have less hardening (which is what you want). Initially, I used cam gears from a car engine to crinkle, but the corrugations were too big (and deep) resulting in the ribbon being too sloppy. I've found some rubber floor grip with 1mm grooves which works great for corrugating.
The thick-foil ribbons work fine until you get to 20mm, then the stiffness of the foil starts to cause some nasty resonances in the horizontal. I tamed mine with a very thin PVA coating. Thinner foil would really help here.
So technically they aren't true ribbons any more...
Soon I will have the transformer inside the feedback loop of the amplifier (like most decent valve amps).
If you dont mind super-directional sound in the vertical axis(makes it sound like you have no ceiling), ribbons offer an amazing amount of detail. The transient response is simply superb.
Oh yeah- and dont bother unless you buy some neo magnets. Check out John Whittaker's site:
http://www.snippets.org/alsr/index.php3#SIZE
Chris
I have built several succesfull ribbon/planar drivers from scratch. Much to hard to descibe in a post. For those of you who would like to experiment I have the unobtainable..(trust me on this) .....the thinnest aluminum foil you will be able to find anywhere . 1/2, 3/4 , and 1 1/2 inches wide. I have Lots of it. Practically free for you( I'd like you to at least give me a couple bucks for shipping!). I'll be happy to help you fellows out. Simply contact me.
Ed Schilling
www.thehornshoppe.com
Ed Schilling
www.thehornshoppe.com
