DIY'ing ribbon drivers?

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fr0st

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Joined 2002
#1
Hi all
From all the comments I've seen, most people rate ribbon drivers quite highly and there apparent simpilicity makes them quite apealing to DIY.
The plan sofar is to get the left over copper copper foil (25 micron, 4mm wide) as the ribbon for starters. I also have left over mylar from some ESL making if it requires some extra strength.
I just have a few questions related to the constructions of the ribbons themselves.
Is it ok to run two ribbons down the one gap, one above the other?
or... can I use the mylar to insulate between two copper strips (effectively one ribbon)? The only problem is that the ribbon would be alot stiffer as opposed to a single. (lower effieciency?)
In order to keep up with 6.5" driver in a two way speaker, what sized driver would be best suited? (or perhaps a name of a comercial driver that can for reference)
If anyone has ony other advice please feel free to share 😀


Thanks
Matt
 
#2
Hi Matt,

I did not want your thread to go unanswered. You may have entered territory a little too strange for most of the active posters.

You also have some design challenges ahead. While ribbons are relatively easy to construct, they pose two challenges. They require extremely strong magnetic fields and they have very low impedances unless you go to a printed circuit/race track design "ribbon." The Parts Express PT2 (and the old infinity EMITs) is an example of this quasi ribbon design.

The strong magnets can be delicate and even dangerous (to fingers) to assemble, and the low impedence of the true ribbon can require transformer coupling. Both make this a much more difficult construction project.

Copper is not typically used because of its higher mass and lower heat conductivity. The heating of the ribbon will make it expand and deform. This deformation makes "slapping" and then arcing very likely in the two layer ribbon design you envisioned. I remember watching the old Gold Line ribbon speakers that actually had the vapor deposited gold conductor visably deform from 4 meters away at merely moderate listening levels. For heating problems, aluminum is still the metal of choice in ribbons. The heating also makes polymers suitable for electrostatics unsuitable for ribbons.

If you can find anyone with an old Speaker Builder magazine collection, I know they printed a couple of articles on ribbon construction. One artcle unrolled a metal foil capacitor to source the ribbon. This might help you formalize your design.

Good luck with your project and try to get to doing instead of just thinking,

Mark
 
#9
Thank you for your replies

I'm going to experiment with the ribbon (seems like noone from the diy scene had published anything about thier success and failures anywhere) but it seems like aluminium looks the most promising from your surgestions (and commercial usage).
From the pictures orca have of the Raven R3 in the datasheet, the ribbons looks about 17cm long and 1.5cm wide and is highly corrugated. One thing that is puzzling me is how they keep the corrugations if the ribbon is highly tensioned? (I'm assuming it would be to reduce the time it take to reach its rest position to retain the accuracy there renound for)
For the magnet structure, I'm going to use neodymium but i'm unsure whether to use lots of smaller magnets (10mm diameter x 3mm thickness) lined at the the edges of the ribbon (no top plate) or have four larger magnets (15mm diameter x 20mm thickness) and use a top plate.

They require extremely strong magnetic fields and they have very low impedances unless you go to a printed circuit/race track design "ribbon." The Parts Express PT2 (and the old infinity EMITs) is an example of this quasi ribbon design.
Click to expand...

I was considering a running multiple smaller ribbons but that would require the ribbon to be looped back around (from top to bottom out of the magnetic field) which would no doubt create inductance so I abbandoned the idea.

Copper is not typically used because of its higher mass and lower heat conductivity. The heating of the ribbon will make it expand and deform. This deformation makes "slapping" and then arcing very likely in the two layer ribbon design you envisioned. I remember watching the old Gold Line ribbon speakers that actually had the vapor deposited gold conductor visably deform from 4 meters away at merely moderate listening levels. For heating problems, aluminum is still the metal of choice in ribbons. The heating also makes polymers suitable for electrostatics unsuitable for ribbons.
Click to expand...

I've seen a picture of a ribbon tweeter that uses heatsinks at the top and botton of the ribbon which seemed to me like an obvious solution to the heating problem. Although the heat disapation would ultimately be limited by the thickness of the ribbon.

The plan sofar is a 17x1.5cm corrugated ribbon, a horseshoe piece of steal with the gap lined with 3mm thick neodymium & small aluminium heatsinks on the ends of the ribbon.
I have intentionly missed out the transformer for now but after electrostat transformers they don't look that hard :dead:

Thanks again for your replies
I thought the thread was doomed for a while there

Matt
 
#13
fr0st said:

One thing that is puzzling me is how they keep the corrugations if the ribbon is highly tensioned? (I'm assuming it would be to reduce the time it take to reach its rest position to retain the accuracy there renound for)
Click to expand...

Pure ribbons are not highly tensioned. They don't move much, so it doesn't take much force to move them back to the rest position.

True ribbons use a very thin and fragile diaphragm, some of these can be broken with a puff of air.

You can make a planar magnetic speaker easier than a ribbon....
 
#14
Ron E said:
True ribbons use a very thin and fragile diaphragm, some of these can be broken with a puff of air.

You can make a planar magnetic speaker easier than a ribbon.... [/B]
Click to expand...

Don’t think so 😉 Have made several times new ribbons for my DK30’s. The trickiest part is to cut the aluminium. It will tear very easily. Have good results with a cutter for photo paper. Corrugation is not difficult. Simply make two staircases from layers of cardboard and press the aluminium ribbon between, et voila.

Have a look here: http://www.xs4all.nl/~rabruil/ribbon.html

(Scroll down the page)

Cheers 😉
 
#15
Thanks for your comments

E-Speakers.com has some early info on some new ribbon drivers
that are a little different. It looks like the horseshoe magnet structure has been replaced with a round ferite magnet with
a notch cut out......
Click to expand...
Those, I believe, are the heil type Al.M made except with a round magnet like you said. The Manager looks like an interesting design... might be the next project :att'n:

Don’t think so Have made several times new ribbons for my DK30’s. The trickiest part is to cut the aluminium. It will tear very easily. Have good results with a cutter for photo paper. Corrugation is not difficult. Simply make two staircases from layers of cardboard and press the aluminium ribbon between, et voila.
Click to expand...

Thanks for the tips. Do you just use plain old aluminium kitchen foil or did you track down a more pure alternative?

To those who have Ribbons that don't mind taking a peek inside, how large are the magnets they use?
I found some picture of the Raven R3.1 in a semi exploded view and it uses quite large pieces of neodymium the length of the ribbon (17cm) and propably a few cm thick which does explain its >100db efficiency.
If anyone can surgest a good magnet structure I can order them straight away and get started on construction 😀
 
#16
fr0st said:
Thanks for the tips. Do you just use plain old aluminium kitchen foil or did you track down a more pure alternative?
Click to expand...


Hi Matt,

The original thickness of the DK30 ribbons is 10 µm. Since I am bound to the transformer ratio of the DK30’s I used kitchen foil of 10 µm thickness to get the proper speaker impedance. Plain kitchen foil works fine but it takes some effort to find it with a thickness of 10 µm, it is one of the thinnest available. Most generic kitchen foil is around 25 - 50 µm.

For the induction in the gap you need something between 0.5 and 1 Tesla, the higher the better. To get that means huge magnets and as Mark pointed out such magnets develop high mechanical forces, so you need a strong mechanical structure. I think it is best you get Justus Verhagen’s book first before you continue (although I did not read it myself) and/or get a good engineering textbook about calculating magnetic circuits. With given gap size and induction you can calculate the magnetic “power” you need. After that you can choose the right magnets.

Cheers 😉
 
#17
Volenti,

Thanks for the correction on thermal conductivity. Copper is almost twice as good at conducting heat than is aluminum. I am wrong again.

Hi all,

Just a thought...Staying within the realm of "pure" ribbon tweeters, the Decca is a proven design with an easy to fabricate horn. Perhaps a good approach would be to start with duplicating the Decca and then scale up to a taller (longer) ribbon and magnet structure.

A low leakage magnet structue should also be relatively easy to fabricate. High permeability steel is best, but is harder to find and more expensive. Instead, using what is known as soft iron (30 to 31 Rockwell scale hardness) in an "U" profile, line the open end of the "U" (along the inside lip) with neodymium magnets.

The construction challenge is how to securely hold the magnets in place. If you are using premagnetized magnets, the easiest way would be a wood jig to position the magnets, and then glue and wires to permanently attach them and complete the magnetic circuit. The pole orientation should be to face the other magnet across the open mouth of the U. The thickness of the magnet (pole to pole) will define the gap depth. The wire (used for a safety measure as a last resort to hold the gap open) should be small gauge and non magnetic.

I have not made this magnetic circuit, so I cannot personally attest to its appropriateness, but it is a classic magnetic circuit and should with properly dimensioned neodymium magnets provide a high flux density in the gap, even with soft iron.

Keep in mind that there is no problem with too high of a field strength and that not all neodymium is the same. Some formulations have higher force per unit mass than others.

Since you will be building small quantities you will have to use a lot of stock parts. Without knowing what is available to you, it would be pointless at this stage to talk about concrete numbers. For the small constructor, it is always a good idea to do a too small prototype, test and get numbers, and then scale as needed.

Please keep us posted, and if you want to build your own numbers in simulation, FEMM (Finite Element Method Magnetics) is a free download at: http://femm.foster-miller.com/index.html

Again, best of luck and have some fun with the doing,

Mark
 
#18
The La folia design looks like an Apogee copy.

As far as I know Apogee was the most succesfull in making full range ribbons. There is a lot of information on te web explaining them and you can also get spare parts that might be usable in your DIY designs.

If you want too I can send your the remainders of the ribbons from a pair Apogee Calipers, I'm installing new ribbons on them and maybe you can use pieces of the big apogee ribbons too make smaller ribbon tweeters.

Take a look here to get an idea of their construction
 
#19
A low leakage magnet structue should also be relatively easy to fabricate. High permeability steel is best, but is harder to find and more expensive. Instead, using what is known as soft iron (30 to 31 Rockwell scale hardness) in an "U" profile, line the open end of the "U" (along the inside lip) with neodymium magnets.
Click to expand...

Sounds OK, but don't worry too much about the permeability of your return circuit. Ribbon motors have wide air gaps, so the high reluctance of air is almost always the limiting factor in flux flow. Do a quick 'n dirty FEMM sim, then compare permendur, soft iron, etc. with cheap steel--surprisingly little difference in the gap field.
 
#20
Can second that Bill,

You can look for the best (expensive and hard to get) cobalt steel but you gain not much. Soft construction steel with low carbon content, like C10 or steel 37 performs pretty well, is cheap and readily available. µ starts to drop at 1 Tesla and saturation comes in at 1.5 Tesla. If you can manage to get that induction anyway with permanent magnets you are doing damn good.

Cheers 😉
 
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