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Old 10th September 2012, 11:31 AM   #11
hanski is offline hanski  Finland
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Thanks Tvi for the links.One of the patents is about ribbon end damping.
This picture shows Apogee Full Range midrange ribbon end clamping:
http://i818.photobucket.com/albums/z...Range_Fig5.jpg
The ribbon end clamping doesn't have any special damping. To me it sounds like it should be possible to make a good ribbon without any special ribbon end damping.

However this picture shows, if I see correctly, several foam pads along the length of the ribbon:
http://i818.photobucket.com/albums/z...Range_Fig3.jpg

Does anyone have a better picture of those foam pads?
Or perhaps comments about them?
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Old 11th September 2012, 05:59 AM   #12
hanski is offline hanski  Finland
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Last night I took Marveloudio advice and did pink noise testing. The ribbon under test was pure aluminium ribbon without plastic backing and with corrugation style closest to Apogee Full Range and Scintilla corrugation pictures found from the web.

The extra noise caused by ribbon resonances was very easy to hear. In my case it was a bit like wind blowing into metallic pipe.
I started by adding foam pads here and there along the length or ribbon, but their effect was marginal. I even tried foam pads glued with silicone to the ribbon, but no help.

Then I tested increasing ribbon tension. Increasing tension decreased noise frequency and also decreased noise amplitude. The end result was a bit more pleasant sound than with my plastic backed multitrack ribbon. Before adding the tension the fine pitch corrugation pure aluminium ribbon was my worst sounding ribbon.

What a learning experience!
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Old 12th September 2012, 02:39 AM   #13
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Hi Hanski. A few of the electrostatic threads spoke of using a felt sheet suspended immediately behind the speaker to damp resonances. I think in some cases, it was glued to the rear stator. I know there is no rear stator here but perhaps carefully chosen material might offer some damping if attached to the frame?
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Old 12th September 2012, 07:43 AM   #14
a.wayne is offline a.wayne  United States
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Your ribbon is too wide , better to break up into two ribbon drive units using the same 4 elements . The resonances you guys are suffering from is because you are corrugating the full length , corrugating is ok If you plan to run for bass or frequency below 1k , flat ribbon with Mylar backing will have less Resonance issues , corrugating the ends only for suspension and household foil has no memory doesn't do well in retaining tension ..
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Old 12th September 2012, 10:55 AM   #15
hanski is offline hanski  Finland
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Thanks guys for the responses,
I know I don't have the required experience/intelligence to design a good ribbon.
So my best bet is try to copy an existing design. I would be very happy achieve even small part of the performance of the original Apogee speakers.

Here are two pictures of Apogee Full Range and Apogee Scintilla midrange ribbons. My understanding is that they are about 50mm wide and 15um and 12um thick pure aluminium:
http://www.abload.de/img/dscn0263w14.jpg

https://lh4.googleusercontent.com/-t...0/IMG_1614.JPG

Based on the pictures, would it be bold to guess that they both have been run through the same corrugation machine?
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Old 12th September 2012, 12:51 PM   #16
a.wayne is offline a.wayne  United States
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The corrugations are very shallow , are you able to duplicate along with the same foil ..? How are you driving the foil directly , even with 4 your impedance will be in 1 ohm range ..
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Old 13th September 2012, 06:15 AM   #17
hanski is offline hanski  Finland
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I could try to duplicate Apogee corrugation if I knew how many corrugations/pleats they used per inch or cm.

Would somebody be so kind and measure how many corrugations per cm/inch does Apogee Scintilla or Full Range have?

I have attached a picture of my finest pitch corrugation (the pure aluminium one).
I guess one difference is that my corrugation is triangle wave and Apogee used sine wave style corrugation? Any comments to this?

And the amplifier is diy single ended Mosfet source follower without feedback.
My 70mm wide single trace ribbon is about 0.125 Ohm and amplifier bias current is 10A with 8V supply voltage.
My 70mm wide 4 trace ribbon is about 2 Ohm and used amplifier bias current was then 4A with 18V supply voltage.
Attached Images
File Type: jpg ribbon.jpg (113.1 KB, 385 views)
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Old 13th September 2012, 08:12 AM   #18
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Why don't you use resistors to get the impedance to where you want it. I use resistors to get to 4, 8, 16 ohms, so you can use any amp and the different outputs on your amps as well! Have built many full range planars and I never corrugate my aluminium foil, stuck on 12um mylar C. Have built from A4 size up to 7' x 2' and am in the process of building 2 headphone designs. Resonance is usually caused by a loose diaphragm, which must be very tight like a drum skin.
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Old 14th September 2012, 09:50 PM   #19
hanski is offline hanski  Finland
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Thanks for the tips Jamesbos. Resistor padding is always a possibility, I have to keep that in mind.
My ribbons are supported at their small ends only, so tightening them to drum skin tension is not possible.
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Old 18th September 2012, 08:50 AM   #20
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I have built some A4 size full range planars with 5.25 x 9 inch diaphragm which sounded good, so I don't see the point of building ribbon tweeters, which need other mid range etc. and complicated crossovers. When you can build a full range one !! You can make the resistance what you want with resistors in series or if too much tape in parallel.
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