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Quasi-Ribbon Experiment, take 1
Quasi-Ribbon Experiment, take 1
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Old 18th June 2018, 12:35 AM   #11
DampedAndDriven is offline DampedAndDriven  United States
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Thanks for your thoughts, woofertester. I'm going to keep tinkering but 'downgrading' from neos and better measurement gear both make sense. Tricky business!
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Old 18th June 2018, 05:28 AM   #12
solhaga is offline solhaga  Sweden
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Note that you can only use conventional field intensity measurement tools up to a certain level of flux.
Generally speaking, it can be used with ceramic magnets but not with neodyms.
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Old 18th June 2018, 01:11 PM   #13
lowmass is offline lowmass  United States
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There is very little to gain with the flux manipulation from the Mu ribbon AND there is a HUGE loss from its mass and resistance.

The ideal practical metal is aluminum.

Transformers for ribbons are far easier than most realize. All the hype about Amorphous metals and exotic winding goes out the window in these designs.

To experiment I would just order some ferrite cores from Digi Key similar to this..

ETD59/31/22-3C97 Ferroxcube | Magnetics - Transformer, Inductor Components | DigiKey

and get some magnet wire from similar places, and wind your own by hand. Keep leads to ribbon short ( and or close together), and use foil .0007 inch thick or less on ribbon and you can easily get response to 20 K hz.
Good place to start is 24-20 gauge primary wire and just parallel 4-6 of those for your secondary or use copper foil ( about .005 to .008 in thick). Many ribbon transformers have about 50- 70 turns pri and 3-5 turns secondary. Dont fuss too much here. That last statement will start a fire with some . Perhaps they have special ears but Ive been doing this for 30 years and have all the different transformer designs at my disposal. The standard simple winds and silicon iron or even cheap ferrite cores stand toe to toe with the exotics in low resistance ribbon design. The ribbon diaphragm design MUCH more important

There is nothing special going on in commercial ribbon transformers. Dont get swayed by the hype, roll your own

THE issue with a good ribbon is 90% in the ribbon diaphragms design/build. This is where the hard work is. Getting a smooth glitch free response all the way out with a low crossover point in a design that can put up with abuse is a very rare thing.

Small narrow ribbons are easier to accomplish this ( but with higher crossover point ) BUT IMO the gold is getting a wider larger surface area ribbon ( not more than 1 inch wide) to do it so that a lower crossover point can be used.

Last edited by lowmass; 18th June 2018 at 01:22 PM.
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Old 18th June 2018, 09:44 PM   #14
DampedAndDriven is offline DampedAndDriven  United States
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Thanks Solhaga for the gear tip, and lowmass for the transformer encouragement! I was hoping somebody would chime in with that. Ok sure, I've already got magnet wire; for $6 why not have a go at winding a transformer.

I respect the many voices of experience saying the mu metal concept is a red herring, but I've got to go through the process of seeing for myself. Should be able to report empirical confirmation or disconfirmation of the FEMM results in 7-10 days.
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Old 19th June 2018, 05:39 PM   #15
lowmass is offline lowmass  United States
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"but I've got to go through the process of seeing for myself."

thats the spirit . much is learned this way
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Old 2nd July 2018, 04:14 AM   #16
DampedAndDriven is offline DampedAndDriven  United States
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Default conventional wisdom seems upheld...

So, built a test bed and ribbons and got to measuring. The initial plan of mounting mu metal strips on Mylar to provide a greater Sd created too many variables to sort out the issues immediately, so I backed off to just looking at similarly sized ribbons of AL, Cu, and Mu metal at various magnetic air gap widths. And, long story short, so far it seems you all were right: "little to be gained by manipulating the flux", and greater mass and resistivity are killers. Resistivity may be more the problem with these Fe-Ni alloys than mass density, as it is worse by a factor of 20 compared to AL, versus "only" a factor of 3 for density. From looking at the transfer functions, M and R appear to be equally the enemy of SPL.

Specifically, the mu metal ribbons did not display the FEMM-promised insensitivity to gap width, except maybe they did not suffer quite as much loss in the move from 4" to 8" gap width as did AL. (I didn't repeat that one for copper.) Moot, because even the 4" output was not useable. Moving from almost no separation to 4" separation with the mu metal ribbon dropped the output level significantly (-30 dB or so IIRC), which means the idea is not working as hoped. I was surprised that AL made noise at all at 8" separation; but there was some signal to be heard even so, with the amp cranked.

A few test bench pics and measurements are attached. I'm left wondering about the 1.7kHz 2nd HD peak the Mu metal and Cu ribbons display. The AL is just kind of ratty everywhere. Any 2HD diagnosis tips?

My other interpretation question is about the "baffle step" looking rise from 1k to 5k. But it's 20 dB not 6, and dipole roll off wouldn't plateau on the low end like that. Right?

The ribbons were all flat (uncorrugated), 0.5" x 4" (moving part between the clamps). AL was the thinner grocery store foil, 0.6 mil says Reynold's website, although it was the store's generic version. Copper was an adhesive conductive tape not much thicker than the AL, but folded in half from 1" to the 0.5" width, doubling thickness. Mu metal was 50 micron, thinnest I could source. Measurements were on-axis horizontally, maybe an inch below axis vertically, at 10" distance. In the pics, the AL ribbon (blue edges) is shown in the minimal gap, magnets to the inside configuration; the mu metal ribbon is shown in a whimsical, magnets turned to the outside of the 'narrow gap' post position. The other two sets of holes in the crosspieces are the 4" and 8" widths.

I may keep playing around with variations, since the overhead of building the test bed is already done. And correlating measurements to math model to better understand expected performance. Wish I understood in detail why FEMM results were misleading. The adventure continues.

Cheers,
-P
Attached Images
File Type: png ALRibbon_smallGap.png (293.1 KB, 107 views)
File Type: png CuRibbon_smallGap.png (243.5 KB, 105 views)
File Type: png MuMetalRibbon_smallGap.png (242.2 KB, 106 views)
File Type: jpg IMG_20180630_130322.jpg (585.7 KB, 107 views)
File Type: jpg IMG_20180701_221851.jpg (977.5 KB, 104 views)
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Old 2nd July 2018, 01:30 PM   #17
lowmass is offline lowmass  United States
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could be a number of things going on

1- to get accurate comparisons of HD you will need to use the exact same setup for each ribbon AND adjust amp so that you have the same loudness for each at around 1 Khz. This means the heavyer ribbons will need a lot more watts to keep up with the AL ribbon.
2- Peaks in distortion plots are usually resonances in the ribbon. The heavyer ribbon look better damped BUT have issues at certain areas. However again u will need to get their volume matched to the AL ribbon to really know.
3- To see the peaks change just grab one end of the ribbon and change its tension. Or corrugate and see where the peaks are. Also pull on corrugated version and watch the peaks change position as the corrugations size is changed by pulling ribbon.
4- the rise in responses is typical low mass diaphragm response.
5- also the different ribbon resistances, IF all used with same transformer wil yeald very different resistance to your amp wich may or may not give some change in high freq response. Some times to see actual response of a ribbon I will get rid of transformer and just run a resistor making all the ribbons same resistance.
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Old 2nd July 2018, 09:47 PM   #18
DampedAndDriven is offline DampedAndDriven  United States
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Quote:
Originally Posted by lowmass View Post
could be a number of things going on
Wow, thank you lowmass, that's all great intel!
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