Linesource:
Can you describe the method of making those "bumper stops" so that the ribbon will not leave the magnetic field from wind movement?
Can you describe the method of making those "bumper stops" so that the ribbon will not leave the magnetic field from wind movement?
gl said:
Where did you get your 5 micron foil from???? I can't PM you or email so I hope you look at this page
Audiophilenoob said:
For a tweeter, the Magnepan replacement information in post #94 does a good job of explaining how to use shims to establish a uniform ribbon-to-pole spacing, and how to use a few drops of a goo like silicone or latex rubber at slightly irregularly spaced intervals along the pole pieces to maintain the gap, reduce resonances, and guard against excessive air puffs.
Different techniques would be used for a midrange ribbon.
When you stack several small magnets together you will have about a 10% lower flux than one single magnet due to fringing fields, air gaps, and the metal coatings. Hence, your simulations may be optimistic.
LineSource said:
ok... I figured there would be some loss... but 10% seems like a lot
the actual flux gap would be closer to .75 T with that in mind...
So with the shims... you would do a 4-6 mm gap like this
<shim>
ribbon
<shim>
????
that way it would allow for full excursion while playing but stop movement that's not controlled?
I'm assuming this is it's purpose
Hi Audiophilenoob,
Your question is answered in post #80. I realize that it's a pretty lame answer for your purposes.
Your best bet is unrolling a selection of film and foil capacitors.
Graeme
Your question is answered in post #80. I realize that it's a pretty lame answer for your purposes.
Your best bet is unrolling a selection of film and foil capacitors.
Graeme
Whacky Femm Results
Excellent work Denis !!
I am going to follow your lead and build my own ribbon. I downloaded Femm v.3.4.2 and started playing around with different frame layouts with disappointing results. I then decided to step back and try to replicate your reults shown here...
http://www.diyaudio.com/forums/attachment.php?s=&postid=558595&stamp=1106510686
This is what I get instead....
...around .5 B in the gap..hmmm.
Here's a shot of the editor window...
...and I've also attached the Femm file if anybody would care to look at it.
Clearly I must be doing somthing wrong, and I would greatly appreciate it if someone could point out what exactly.
Thanx,
Casey
Excellent work Denis !!
I am going to follow your lead and build my own ribbon. I downloaded Femm v.3.4.2 and started playing around with different frame layouts with disappointing results. I then decided to step back and try to replicate your reults shown here...
http://www.diyaudio.com/forums/attachment.php?s=&postid=558595&stamp=1106510686
This is what I get instead....
An externally hosted image should be here but it was not working when we last tested it.
...around .5 B in the gap..hmmm.
Here's a shot of the editor window...
An externally hosted image should be here but it was not working when we last tested it.
...and I've also attached the Femm file if anybody would care to look at it.
Clearly I must be doing somthing wrong, and I would greatly appreciate it if someone could point out what exactly.
Thanx,
Casey
I just looked at the pictures of the femm results side by side on a different monitor (the one hooked to the pc to post) and they look a lot closer than I originally thought... is .5 correct then ?
Thanx,
Casey
Thanx,
Casey
valveitude
The steel cross pieces at the top and bottom are flux saturated, and the air flux path is the center is much weaker. Try adding 2 or 3 pole-to-pole steel cross supports in the back of the ribbon to create additional flux paths. You can also model significantly wider steel at the top and bottom for comparison.
If you are not committed to a dipole, you can create a full steel "U" section and stuff the cavity with absorption material.
The steel cross pieces at the top and bottom are flux saturated, and the air flux path is the center is much weaker. Try adding 2 or 3 pole-to-pole steel cross supports in the back of the ribbon to create additional flux paths. You can also model significantly wider steel at the top and bottom for comparison.
If you are not committed to a dipole, you can create a full steel "U" section and stuff the cavity with absorption material.
Hello Linesource...
True enough, but the pole pieces in dhenryp's simulation I linked above are as well. Thats not to say thats ok, I plan on a 1"x1" cross bar every 3" inches or so. I just want to make sure I'm running Femm right.
This might have been answered in this thread, but what flux density can I expect in the gap?
Thanx,
Casey
True enough, but the pole pieces in dhenryp's simulation I linked above are as well. Thats not to say thats ok, I plan on a 1"x1" cross bar every 3" inches or so. I just want to make sure I'm running Femm right.
This might have been answered in this thread, but what flux density can I expect in the gap?
Thanx,
Casey
valveitude - I got ~ .67 tesla which seems to be what you got. The peak in the steel is ~ 1.95 which is approaching saturation for 1018 steel (the knee of the saturation curve is ~ 2 tesla). If you made the frame thicker, or added additional crosspieces as linesource suggested, you could pick up ~.15 tesla, based on a quick femm run I just made. I should have made the frame thicker but I doubt the result would be much more than a db of extra output
I have some concerns about adding cross pieces in back of the ribbon. Unless you make it a pretty deep "U" shape, I think you would have a pretty big reflecting surface right next to the ribbon - the destructive interference might lose you the db you pick up with extra field strength. FYI: I'm running my ribbon as a monopole by putting it in a box. The back of the box is ~5" from the ribbon which gives me plenty of room (I hope) for felt and foam to absorb the back wave.
Regards,
Denis
I have some concerns about adding cross pieces in back of the ribbon. Unless you make it a pretty deep "U" shape, I think you would have a pretty big reflecting surface right next to the ribbon - the destructive interference might lose you the db you pick up with extra field strength. FYI: I'm running my ribbon as a monopole by putting it in a box. The back of the box is ~5" from the ribbon which gives me plenty of room (I hope) for felt and foam to absorb the back wave.
Regards,
Denis
Hello Denis,
Where are you measuing this ? When I click on the gap center,an equal distance from both magnets, I get about .5. Are you looking at the magnet surface ? The flux varies across the gap, I don't know where the "proper" measuring point is.
This is very exciting to me. I got the ribbon bug about 20 years ago, and actually got as far as a 24" prototype using ceramic magnets saturating steel pole pieces. It was very promising, but a combination of not being willing to use a tranformer, and my son's birth shifting my priority's, I dropped the project. Well my kid is almost grown, and I have had a paradigm shift in my attitude towards transformers. Add to that a ready supply of rare earth magnets and tools like Femm, and its time to finally follow through 😀
Casey
Where are you measuing this ? When I click on the gap center,an equal distance from both magnets, I get about .5. Are you looking at the magnet surface ? The flux varies across the gap, I don't know where the "proper" measuring point is.
This is very exciting to me. I got the ribbon bug about 20 years ago, and actually got as far as a 24" prototype using ceramic magnets saturating steel pole pieces. It was very promising, but a combination of not being willing to use a tranformer, and my son's birth shifting my priority's, I dropped the project. Well my kid is almost grown, and I have had a paradigm shift in my attitude towards transformers. Add to that a ready supply of rare earth magnets and tools like Femm, and its time to finally follow through 😀
Casey
Hi Casey,
I was measuring at the center of the gap, which is the worst case measurement. I downloaded your file and tried it at work and got ~.53 tesla. I'll try it again at home tonight and also post my file. I might have messed up last night.
Regards,
Denis
I was measuring at the center of the gap, which is the worst case measurement. I downloaded your file and tried it at work and got ~.53 tesla. I'll try it again at home tonight and also post my file. I might have messed up last night.
Regards,
Denis
Hi Denis,
Yep..thats what I get. If you get a different result at home, it might be worthwhile checking the version number of Femm to see if its different. I had a comparable discrepency with an unrelated program, and it turned out my "better" results was from an older version...just a thought.
Thanx for the effort,
Casey
P.S. I was surfing your site and was curious...do you still follow family tradition and carve the poulty dental implements, or have you given in to modern manufacturing ? Either way, I'm sure the family fortune is in good hands.
Yep..thats what I get. If you get a different result at home, it might be worthwhile checking the version number of Femm to see if its different. I had a comparable discrepency with an unrelated program, and it turned out my "better" results was from an older version...just a thought.
Thanx for the effort,
Casey
P.S. I was surfing your site and was curious...do you still follow family tradition and carve the poulty dental implements, or have you given in to modern manufacturing ? Either way, I'm sure the family fortune is in good hands.
Someone once mentioned aluminum leaf as ribbon foil
http://216.105.59.114/index.asp?PageAction=VIEWPROD&ProdID=252
It's called "compositon" I would call first and see what that means 😉
http://216.105.59.114/index.asp?PageAction=VIEWPROD&ProdID=252
It's called "compositon" I would call first and see what that means 😉
Variac - I have a package of that Aluminum leaf from Constantines and it is much to thin to use as a speaker ribbon. Just touching it with you fingers is enough to tear it.
Casey - I had changed the file I had at home so it no longer represents the ribbon I built. Your femm file is correct.
PS
I am still hand carving domestic fowl oral appliances although that now takes a back seat to my speaker "work". It's just as well, I haven't sold sold a set of hen dentures since 1978.
Casey - I had changed the file I had at home so it no longer represents the ribbon I built. Your femm file is correct.
PS
I am still hand carving domestic fowl oral appliances although that now takes a back seat to my speaker "work". It's just as well, I haven't sold sold a set of hen dentures since 1978.
Transfomer Calc
Denis,
How does the transformer perform now, are you happy with it.
Did you thought of using a POT core?
Denis,
How does the transformer perform now, are you happy with it.
Did you thought of using a POT core?
Now that I think of it, the alu leaf was recommended for ribbon microphones, not tweeters. Might even be impossible to use for mics...
Variac - I've seen web pages were they show how to make ribbons for microphones so I believe that works - much less excursion than a driver and practically no current in a microphone.
Mallickarjuna - I've only tried the toroidal core. I am happy with it but I've had no additional experience since my earlier posts.I've spent the last couple months on enclosures for the ribbons and a line array. I'm nearly done and hope to have it together to try out next week.
Regards,
Denis
Mallickarjuna - I've only tried the toroidal core. I am happy with it but I've had no additional experience since my earlier posts.I've spent the last couple months on enclosures for the ribbons and a line array. I'm nearly done and hope to have it together to try out next week.
Regards,
Denis
Some of the best ribbon microphones I have read about use 2 micron pure aluminum foil. A typical microphone ribbon is 0.2 inches wide and between 2 and 4 inches long. A local JFET amplifier is sometimes used on place of a step up transformer on a microphone.
The Magnapan tweeter ribbon is 2.5u thick, 0.2" wide and 72" long. You can break the foil with a strong, close puff of air. Several small dots of adhesive are used between the ribbon edges and pole piieces to keep the ribbon from sagging and twisting in the SPL.
5.8u aluminum foil is the thinnest I find robust enough for normal use and abuse.
The Magnapan tweeter ribbon is 2.5u thick, 0.2" wide and 72" long. You can break the foil with a strong, close puff of air. Several small dots of adhesive are used between the ribbon edges and pole piieces to keep the ribbon from sagging and twisting in the SPL.
5.8u aluminum foil is the thinnest I find robust enough for normal use and abuse.
Finished Line Arrays!
See this thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=60373
See this thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=60373