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Old 16th May 2017, 10:52 PM   #31
urmom is offline urmom  United States
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Quote:
Real hands on development work will educate. Often finding out that our presumptions of technical "correctness" are well past the point of diminished returns or even just plain wrong.
True enough but I'm obsessed with perfection and details when it comes to this stuff. I like to think things through thoroughly and reach the best theoretical conclusion before I officially build.

What do you think about clamping the ribbons down between two pieces of rubber at the bracket? If I use an aluminum or plastic bracket I can only imagine some of the vibration from the ribbon transferring to the structure which would cancel out some of the sound.

If you look back at the pictures I posted earlier you'll noticed I had a clamping piece. I'm thinking about sandwiching a similarly shaped rubber clamping piece between it and the bracket along with another rubber piece sandwiched between the bracket and the underside of the ribbon.
This would squish the ribbon between compressed rubber and keep the structure vibrationally quiet.
Along these lines I'm wondering what you meant when you spoke of ribbon with no pleat between "strange suspension". Do you know anything about this method?

Last edited by urmom; 16th May 2017 at 11:01 PM.
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Old 17th May 2017, 12:38 AM   #32
urmom is offline urmom  United States
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Here's a picture of what I mean.
I updated the structure to have no barrier between the ribbon and the magnet and added some structural support in the back to keep the ribbon slots stable which isn't visible in the picture.
I included the rubber parts I was talking about shown in black.
2017-05-16.png

The top rubber piece gets squished between the top bar and the bracket and ribbon and the bottom rubber piece slides in between the slots in the middle of the bracket serving as the "floor" for the ribbon, not counting for compression the top of the rubber "floor" would be at the magnetic midpoint.
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Old 17th May 2017, 11:10 AM   #33
lowmass is offline lowmass  United States
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some comercial ribbons use a "rubber clamp" at the ends similar to what u say. This is to provide a strain relief and maybe some damping. This helps reduce cracking of ribbon at the termination points.

With a pleated ribbon the entire ribbon is a spring of sorts so it easily moves back and forth. a straight non pleated foil is very stiff ( if its a short ribbon)so if doing bass(larger moves) it needs some compliance in the form of a springy suspension at the ends. There are probably an infinite number of ways to do this limited only by your imagination. Just think of a soft springy way to mount ribbon at ends.......

Last edited by lowmass; 17th May 2017 at 11:12 AM.
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Old 17th May 2017, 04:35 PM   #34
urmom is offline urmom  United States
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Other than an actual spring I'm not coming up with much.
Jello?
The most realistic thing I'm thinking of is maybe using a rubber clamp compressed between sponge material but it depends on how much mechanical force the ribbon actually exerts upon the structure at low frequencies.
I don't know if rubber and foam are going to be too much of a dampening force to overcome for the ribbon.

On another side of things I have a question about driver depth. The magnets in my current design will be protruding about 0.2'' above either side of the ribbon forming a sort of "channel" along the ribbon. Does this affect the sound in some way? Should I keep magnet height to a minimum?
I designed it so the magnets will lay next to each other in the position shown in the photo on this page SUNKEE 4x2/5x1/5-Inch N52 Neodymium Permanent Block Bar Magnet 2 Pieces Should I lay them flat instead?

Last edited by urmom; 17th May 2017 at 04:42 PM.
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Old 17th May 2017, 04:49 PM   #35
lowmass is offline lowmass  United States
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the slot depth will have effect. its a double edged sword in that the deeper the slot the more uniform and stronger the magnetic field, but the shallower the slot the less slot effect. Basically you get a bump in response out at higher frequency's. Many will use a trap circuit electrically to EQ the bump. Some designs are using magnets that are shaped at an angle to help lessen this effect, BUT despite their claims they have some loss of field uniformity and are limited to use above maybe 1.5 khz.Laying those magnets on side will not work well as the poles are in wrong position.

However in a headphone you are not going to drive the diaphragm nearly as hard as in a speaker, so you can get away with less uniform field at least from a reliability standpoint. Exactly how much you can get away with is found by trial and error destructive testing. Also there may not be as much trouble with a slot when the ribbon is close to ear anyway, not sure bout this but it seemed to me in my own experiments that it wasn't a big issue.

Last edited by lowmass; 17th May 2017 at 04:56 PM.
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Old 21st May 2017, 02:23 PM   #36
urmom is offline urmom  United States
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What do you think about using ribbons of different thickness within the same magnetic field? Like using two strips of kitchen foil with a much thinner layer in between. Thicker foil gives lower response right? I'm thinking maybe the two ribbon types might muck up the sound though.
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