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DIY ribbon dipole tweeter, reductio ad minimum
DIY ribbon dipole tweeter, reductio ad minimum
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Old 3rd August 2015, 05:10 PM   #11
marsupialx is offline marsupialx  United States
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You write that the magnets are custom. Where can one source such magnets? Looks like a fun build!
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Old 3rd August 2015, 05:34 PM   #12
Gerrit Boers is offline Gerrit Boers  Netherlands
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Quote:
Originally Posted by zmajz View Post
I like this very much, even I could build it. But, can You show the magnetic poles orientation (N/S or E/W) just to make it clear to me....
Here's the drawing I used to explain it to the people where I ordered them:

Magnet-50x10x4.png

Beware that these are custom magnets so there is a minimum order quantity.

Some more pictures of the construction:

magnet-no7-glued.jpg

Here you see the 7th magnet glued in place. I used a piece of 20mm wide steel strip to align the magnets. The first six magnets are relatively easy to fix, the next six are more difficult. If you're not careful the magnets will slip from your fingers, flip around, and align themselves the wrong way.
Here's a picture of magnet number 8 clamped in place:

magnet-no8-clamped.jpg

You have to really push it against the magnet already glued in place. With all magnets glued in place additional pieces of plywood are are glued at the ends:

magnets-all-glued.jpg

I used 1mm plywood mainly because I had it lying around, of course you can also use other materials.

regards,

Gerrit
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Old 3rd August 2015, 05:54 PM   #13
Gerrit Boers is offline Gerrit Boers  Netherlands
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Originally Posted by marsupialx View Post
You write that the magnets are custom. Where can one source such magnets? Looks like a fun build!
I ordered them at NEOTEXX but any shop that does custom work should be able to provide them. The minimum order quantity for custom magnets at Neotexx is 200,- so that's a bummer but it will get you 100 magnets.

My previous design uses a steel plate to close the field, this will result in a stronger field and you can use standard magnets:

connected-ribbon.jpg

This is not a true dipole but it still works pretty well, I use these for my surround speakers. I plan to make an improved version with dual magnets and a slightly smaller frame:

ribbon_motor_design.png



regards,

Gerrit
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Old 3rd August 2015, 07:08 PM   #14
zmajz is offline zmajz  Croatia
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What do You mean it's not a dipole? As I can see from the photo, it is opened on both sides (front and rear) to radiate in true dipole,or I missunderstood something...
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Old 3rd August 2015, 07:47 PM   #15
bolserst is offline bolserst  United States
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Quote:
Originally Posted by marsupialx View Post
You write that the magnets are custom. Where can one source such magnets?
Here are some regularly stocked magnets I've used for ribbon projects in the past.
They aren't the exact dimension used for this project, but they are magnetized in the desired direction for the construction configuration.

cPath_5 | products_id_360 | Neodymium Magnets N42 Long Bar 3 in x 1/8 in x 5/16 in - Applied Magnets & WindMax Wind Turbines
K&J Magnetics: BX024
K&J Magnetics: BX028
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File Type: png Magnets_for_Ribbons.png (512.2 KB, 1225 views)
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Old 3rd August 2015, 08:45 PM   #16
Gerrit Boers is offline Gerrit Boers  Netherlands
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Quote:
Originally Posted by zmajz View Post
What do You mean it's not a dipole? As I can see from the photo, it is opened on both sides (front and rear) to radiate in true dipole,or I missunderstood something...
It may be a matter of semantics but in my book a true dipole will have a 6dB/oct slope in the response due to the cancellation of the front wave by the back wave. The steel frame is too wide for that, there is no slope in the response and the polar response isn't as good.
Although the 6dB/oct slope requires serious equalisation I it's worth it because of the excellent directivity. The fact that the ribbon has prefect symmetry and excellent directivity results in a very sharp and stable stereo image, much better than the Linkwitz Orion's I had before this system.
Because the ribbon without the steel frame is smaller it can be placed closer to the mid driver which is also beneficial.

regards,

Gerrit
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Old 4th August 2015, 04:45 PM   #17
Rob Dingen is offline Rob Dingen  Netherlands
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Hi Gerrit,

Nice work, i you play al little with the tension of the ribbon you can lose or flatten the distortion peak.
I always use weight to get the same tension.

Rob
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Old 4th August 2015, 05:18 PM   #18
Gerrit Boers is offline Gerrit Boers  Netherlands
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Quote:
Originally Posted by Rob Dingen View Post
Hi Gerrit,

Nice work, i you play al little with the tension of the ribbon you can lose or flatten the distortion peak.
I always use weight to get the same tension.

Rob
Thanks
I was planning to do just that, experimenting with the tension. Don't know if a using weight would work with my design, there is very little room, but I'll keep it in mind. I was thinking of adapting my corrugation contraption so that a fixed length can be corrugated, a bit shorter than the gap height, so I can get the right tension by stretching the ribbon until the corrugation touches the clamps.
As far as the frequency response is concerned the repeatability is excellent:

six-4.6mu-ribbons.png

The graph shows the response for six different ribbons, the red and orange lines are for slightly thicker ribbons (6m vs 4.6m).

regards,

Gerrit
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Old 18th August 2015, 02:12 AM   #19
Few is offline Few  United States
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Very nice work, very well documented! I'm late to this party but wanted to say thanks for sharing your experiences. It's helpful to those of us following related paths.

Few
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Old 18th August 2015, 06:41 AM   #20
Gerrit Boers is offline Gerrit Boers  Netherlands
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Originally Posted by Few View Post
Very nice work, very well documented! I'm late to this party but wanted to say thanks for sharing your experiences. It's helpful to those of us following related paths.

Few
Thanks
That was the main reason for sharing this, so that other people might find some useful information for their own projects or perhaps even build this simple design.

One thing I would like to try is to see if it is possible to create a cardioid by applying damping to the back. This would have the advantage of a constant directivity without the dipole losses.

regards,

Gerrit
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