Inside a Ribbon Tweeter ?

[GRollins]

The Magneplanar planar drivers are not and were never meant to be ribbons. I was referring to their ribbon tweeters.
Jim Winey is the one who received a patent on the direct drive ribbon--i.e. no transformer. They sound very good, indeed. He is directly responsible for the current popularity of ribbon tweeters. They had been exceedingly rare devices prior to the early '80s when he released the Tympani IV. Now they're everywhere.

Grey

[Joules]

The Magneplanar planar direct drive ribbon--i.e. no transformer. They sound very good, indeed.

I would be vey much interested in seeing the design of these Magneplanar direct drive ribbon tweeters.

[dhenryp]

Great pictures Linesource. Do you know what the copper covered block in the back of the Raven is? I might guess it's another big magnet but I don't know why it would be covered with copper. Also, you wouldn't happen to have a picture of the Raven transformer would you? I can just get a peek at it in the picture. I'm wondering if it's EI or torroid.

PS

I got you aluminium samples - THANKS!. I hope to try them this weekend.

Denis

[gl]

The copper covering appears to be a flux band. It's wrapped around either a magnet or steel spacer that's located right behind the transformer. Perhaps they found that there was too much flux leaking from the transformer circuit into the main field circuit. It's interesting that they would have chosen to wrap the adjoining magnetic structure instead of the transformer. I'll bet there was a lot of experimenting before the design was final.

Graeme

[Joules]

Wow ! Great pics, Linesourse. Thanks allot - just what the doctor ordered.
It's interesting to see how othe poeple solve the same problems I've been strugling with. If you got any more keep them coming.

After many many runs with FEMM I come up with a good design of a ribbon tweeter simular to raven and arum cantus high end designs. I've soursed all the materials including the ribbon alum. and the x-former core material. It's not cheep but still considerlbly cheeper than the store bought units. It will be awhile be for I build so there's plenty of time to tweek the design.

As an alternate,I designed a line sourse ribbon that looks interesting on paper. A 40-60 inch long x .25 wide closed back ribbon unit. The ribbon would have a resistance of about 1-2 ohms with enough effiency to put a 2-3 ohm resister in series with it and still have92-96 dB/w eff - no transformer. This is all just vaper at this point but would be interesting to try some day.

[tvi]

You might find this patent of interest
4580014



Regards James

[dhenryp]

Originally posted by gl
The copper covering appears to be a flux band. It's wrapped around either a magnet or steel spacer that's located right behind the transformer. Perhaps they found that there was too much flux leaking from the transformer circuit into the main field circuit. It's interesting that they would have chosen to wrap the adjoining magnetic structure instead of the transformer. I'll bet there was a lot of experimenting before the design was final.

Graeme

I thought it might be some kind of shorting ring like they put in coli driven drivers but I can't understand it in this context. The shorting ring only helps in a varying magnetic field. In the ribbon core the, magnetic field is constant. The only thing I can think of is that it's intended to shield the trasnformer from the varying magnetic field around the ribbon itself. If that's the case, it would seem to be more effective around the transformer, as you said.

[gl]

Hi Denis,

I believe that the flux band here is meant to absorb the stray audio frequency flux from the transformer and keep it from modulating the the magnetic field of the field magnet which, as you say, needs to stay constant. The ribbon itself is too far away and too short to cause a problem. The transformer on the other hand is right up against the metal block. I have a sneaking suspicion that a flux band on a small toriod running at high audio frequencies would cause frequency and phase problems. But that's just a gut feeling.

By the way I second the person who said that the patent office was a great source of info. The patent number for the Winey/Magnepan tweeter referred to in other posts here is 4,319,096.

Graeme

[LineSource]

I've attached a diagram of the Magnepan dipole ribbon. I believe it is about 72" tall and 0.2" wide, built from corrugated 2.5 micron thick aluminum foil. The ribbon is very narrow and very, very thin, and this allows conventional ferrite magnets to create adequate efficiency, plus a high enough resistive impedance for direct drive without a transformer using standard amplifiers. The modest size allows a slotted steel frame construction which gives a complete magnetic circuit around the back plus adequate open gaps for the rear sound waves to create a dipole. Seems like a very nice low cost, mass production design.


The copper ring on the Raven is mainly to isolate the magnetic fields from the transformer, as the currents can be very high on the ribbon side, but it would also provide some shielding of the stray magnetic flux between the sides and back iron pieces, thus increasing the total gap flux plus minimizing how this stray flux might bias the rear movement of the ribbon.

[sam9]

I would be vey much interested in seeing the design of these Magneplanar direct drive ribbon tweeters.

There is a whole section on nothing but over at www.audioasylum.com

One of the patents has the name "Nelson Pass" on it as well.

A major part of why they sound as they do relates to the essential nature of dipoles regardless of how they are otherwise constructed. Siegfried Linkwitz (www,linkwitzlab.com) has info on this. The basic factor is that all dipoles create a "null" orthagonal to the axis of radiation. I'vee seen a demo computer simulation of this. What it means is that there is very little interaction with side walls, floor or cieling. If you ever get a chance just walk past one that is playing. As you reach the point where you are exactly 90 deg to the side, the sound suddenly drops away and almost dissapears -- very wierd sensation.