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Old 31st January 2008, 11:37 PM   #1
fperra is offline fperra  United States
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Default The start of another large ribbon speaker

I didn't want to add on to dhenryp's thread, as it is long enough already so I thought I would start a new one. I just ordered sixty 4" x 1/2" x 1/2" thick, Grade N42 magnets from Applied Magnets for $322 which included shipping. I've also ordered a 10 pound roll of 5" wide by .00035" aluminum foil for $50 plus shipping and some type W ferrite toroidal cores for the transformers. I'll be ordering the steel pole pieces in the next few days as soon a I finalize the design. It will be basically the same as dhenryp's with the following exceptions. I will be using aluminum as the back spacers instead of steel and the gap will be slighty wider to accomidate a ribbon that is 5/8" wide. The only thing left for me to determine is the length. So far I am leaning towards 56" long. That will give me 4 spare magnets in case I have any breakage. The ribbon will be one continuous length instead of a segmented one. The final speaker will consist of the ribbon line source along side of a line source of eight TB W5-704D midranges and two HI VI 10.8 woofers which will be mounted on oposing sides of the enclosure. I already have all the 16 midranges and four woofers and I'm only lacking the ribbon tweeter. I don't expect fast progress on this project, but a I move along I will keep posting with pictures.
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Old 2nd February 2008, 06:18 AM   #2
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Floor to ceiling, 84" - 92" high looks nice.
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File Type: jpg perfect8.jpg (29.7 KB, 634 views)
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Old 2nd February 2008, 02:20 PM   #3
fperra is offline fperra  United States
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Very nice indeed. I see $$$$$$ when I look at those.
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Old 3rd February 2008, 03:19 AM   #4
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fperra,

If you can get steel locally, you may want to consider purchasing the standard 96" long rectangles and using the extra height to make a simple floor mount to a flat plate of aluminum or wood with a rubber base. You can always add magnets later.

Since you mentioned aluminum cross braces, it sounds like you are building a dipole ribbon, which reduces the size of the steel pole pieces from what Valveitude used. If you run a FEMM, you will see strong stray fields, much greater than with iron cross braces completing the circuit. For a dipole ribbon, it is probably best to purchase 0.5" wide steel to match your magnets. The iron will saturate first at ~ 1.1T, so magnet-to-magnet gaps are the most efficient for NdFeB. The Lister Patent is out of date.

Valveitude and dhenryp went to some effort to mount their ribbons in strong wooden frames. A full height ribbon might simplify this construction. I found it important to avoid direct physical contact between speakers and ribbon, like the Perfect_8 photo I attached. I also toe-out my woofer speaker line source to get a longer reflection delay and less wind hitting the 5.8u ribbon.

You can also calculate the resistance of a 56" and 90" ribbon to see if a direct drive amp is feasible. You can use a small series resistance of say 0.5 ohms to pad up to where a DIY low voltage output Krell Klone can direct drive.

Oh......and floor to ceiling does look nice!

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Old 3rd February 2008, 03:58 PM   #5
fperra is offline fperra  United States
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Thanks for the info LineSource. Although I would love to build a taller speaker, my current setup limits what i can do, and that's a speaker about 6 ft. tall. So I've decided to make the ribbon 52" tall. With the batch of 60 magnets I've ordered, that will leave me with 8 spares for breakage, I've already ordered the steel and aluminum from Metals Express. The steel is 5/8" square. By using aluminum instead of steel for the back pieces I would think the field within the gap will be more uniform for one continuous ribbon. Also, since the magnets are N42 vs. N40, and are twice as thick as the ones dhenryp is using, the efficiency should be sufficiently high. If not, I can always add the Iron cross braces later. Are my thoughts regarding iron cross braces vs. aluminum in regards to the mag field uniformity along its length correct?
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Old 4th February 2008, 12:34 PM   #6
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fperra-

Quote:
By using aluminum instead of steel for the back pieces I would think the field within the gap will be more uniform for one continuous ribbon.
That would depend on how saturated the side rails get at the contact point of the back pieces. You need to look at is as a circuit where the flux is current and the steel is wire. As long as you don't exceed saturation of the steel, the magnetic field will be surprisingly uniform. If you haven't already, I would download FEMM and model it. It will work of course the way you have planned it, but as LineSource said, you will have a lot of free floating flux in your room..no TV's anywhere near them .

Where did you source your foil from? I would be interested in buying some.

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Old 5th February 2008, 01:20 AM   #7
fperra is offline fperra  United States
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Only a 65" Plasma. But I don't think Plasma's are affected like CRT's. I got the foil from Comet Metals. They were doing a run for someone else and had leftovers. Thats why I got a great price of $50 for a 10 lb roll. I can't imagine how many feet there will be on that roll, but certainly more than I will ever use.

On another point, I have a number of gear sets for pleating the ribbon. Would you recommend gears with deep teeth or shallow? I have both.
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Old 6th February 2008, 07:57 PM   #8
fperra is offline fperra  United States
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UPS delivered my magnets today; 4"X1/2"X1/2" N42. I knew these would be strong, but man, I gained some new respect for these things. I should have fun taking the bundle apart. I think I'll pull one off at a time as I glue them to the pole pieces.
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Old 7th February 2008, 01:01 AM   #9
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Quote:
I knew these would be strong, but man, I gained some new respect for these things.
Spooky huh . Keep in mind that if you let them slap together they can hit with enough force to shatter..sending shards at high velocity (don't ask me how I know ).

Casey
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Old 7th February 2008, 01:33 AM   #10
fperra is offline fperra  United States
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Next time I'll plan on doing twice the gluing with 1/2 the magnet length.
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