DIY ribbon dipole tweeter, reductio ad minimum

This would be a really interesting candidate for a group buy. Gerrit if you were obligated to buy far more than you need, are you interested in selling off excess. Sounds like there would be lots of takers.

I'm sorry but I already have plans for all the magnets I have. I already have the new steel plates for my surround loudspeakers and I also want to experiment with a ribbon cardioid. It will be very interesting to see how the steel plate with the double magnet motor performs and how low the ribbon can be crossed.

regards,

Gerrit
 
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:

View attachment 496984

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

regards,

Gerrit

I wonder why fountec sometimes uses 15uM membranes in their tweeters..maybe because of reliability problems...

https://www.madisoundspeakerstore.c...neox-1.0-ribbon-tweeter-with-black-faceplate/
 
I wonder why fountec sometimes uses 15uM membranes in their tweeters..maybe because of reliability problems...

https://www.madisoundspeakerstore.c...neox-1.0-ribbon-tweeter-with-black-faceplate/
According to the spec sheet they use a sandwich ribbon, probably as an alternative to corrugation. The average gap flux is 0.4 Telsa (sic) average, it would be interesting to see a graph of the flux density across the gap.
The more uneven the flux density across the gap, the more corrugation is required to prevent flexing of the ribbon.
Here's a picture of a flat ribbon where the flexing is clearly visible:

flat-ribbon-flex.jpg

This is what corrugation is supposed to prevent.

regards,

Gerrit
 
]wow, nice picture!

Do you think I can do some double magnets experiments using 10x10x50 mm normally polarized neodymium magnets?

A 1cm deep cavity will probably cause a resonance in operating range, I would advise against it if your ribbon is about the same width (19mm). It could also prove to be very difficult to glue the magnets in place, they very much like to flip around and with 10mm x 10mm x 50mm magnets this effect will only be stronger. Of course, if you have plenty of magnets lying around you could try it.

regards,

Gerrit
 
Finally found some old foil capacitor, with what i assume is 6um thick alu foil. The difference between it and kitchen foil is night and day in terms of sound quality. I just quickly built 30x2,5cm ribbon, with steel U profile that holds small 30x10x5mm neo magnets. Efficiency is still small, but sound quality is amazing.
Have to make another quasi ribbons for my 1m tall ribbons, using this thinner foil.

If anyone knows what is good source of thin alu foil, please write. I have hard time finding foil capacitors without metalized polyester (mylar).
 
Finally found some old foil capacitor, with what i assume is 6um thick alu foil. The difference between it and kitchen foil is night and day in terms of sound quality. I just quickly built 30x2,5cm ribbon, with steel U profile that holds small 30x10x5mm neo magnets. Efficiency is still small, but sound quality is amazing.
Have to make another quasi ribbons for my 1m tall ribbons, using this thinner foil.

If anyone knows what is good source of thin alu foil, please write. I have hard time finding foil capacitors without metalized polyester (mylar).

Aluminium folie ? belangrijke eigenschappen - Salomon's Metalen

Don't know if they sell to us diy:ers.

If You plan to contact them, let us know...
 
Thanks for the link! I assume they are selling foil to other businesses, like many others. I have found several similar sellers, some of them do sell foil in small quantities (sheets 20x20cm for example), but are expensive. Other sellers, for example from China, are selling 5um foil for capacitors, but we need to buy at least 50kg. (1 kg is about 4-5$). 50kg is probably few kilometers or miles of foil :) , but it is great price.
I will keep looking, and contact few of them to find out. If I find anything interesting, I will post it here.
In the meantime, if anyone knows where at least we can find new polymer foil capacitors (non metalized) that are easy to disassemble (radial ones), please write. I have only 2,5mx2cm 6um foil for now, which is enough for 1 pair of ribbons, but too little for experimenting or making mistakes. Capacitors seem to be cheapest way to getting good alu foil.
 
Etching is interesting, but I must do that carefully in well ventilated area. Only problem is equally etching the foil to get to desired thickness. I can borrow micrometer to measure thickness exactly, but making 1m long foil must be difficult. I assume you can wrap the foil but probably is best to etch straight piece of foil. I will write down your cooking recipe, maybe I would have to do etching if I don't find already made foil.

Wima FKP3 capacitors appears to have structure that we need, but are very difficult to open because they are dipped in resin that is rock hard. (tried on wima mkp which is metalized foil). http://www.wima.com/EN/WIMA_FKP_3.pdf Need to find something similar.
 
Etching is interesting, but I must do that carefully in well ventilated area. Only problem is equally etching the foil to get to desired thickness. I can borrow micrometer to measure thickness exactly, but making 1m long foil must be difficult. I assume you can wrap the foil but probably is best to etch straight piece of foil. I will write down your cooking recipe, maybe I would have to do etching if I don't find already made foil.

Wima FKP3 capacitors appears to have structure that we need, but are very difficult to open because they are dipped in resin that is rock hard. (tried on wima mkp which is metalized foil). http://www.wima.com/EN/WIMA_FKP_3.pdf Need to find something similar.

I did some calculations and in my case there's less than 0.5l hydrogen gas produced over a period of 20 minutes, I don't think that's a problem. If the foil is clean and the solution is gently moved over the foil than it should etch evenly over the whole surface. I didn't use a micrometer but a precise scale to calculate the thickness. For longer ribbon you could use a plastic tube or rain gutter and pump the solution through it.
Specialised foil under 10µm can get expensive very quickly and is hard to get, the materials needed for etching foil are cheap and readily available.

regards,

Gerrit
 
I agree, those types of materials are very easy and cheap to buy in large quantities. Tube sounds like a great solution for longer ribbons, that would be similar to etching a PCB with a pump, just through a tube. That is really a quick way to get foil in thickness that we need, and it would be easy to compare different thicknesses in same magnetic field and obtain measured differences. You gave me something to think about...

I just thought that by unrolling some old capacitor that even I forgot i have laying around, and getting fantastic aluminium foil out of it, it would be easy to do again with new capacitors. But finding non-metalized foil caps in shape that is easy to work with, seems to be little harder than i thought. And they are considered "audiophile caps" these days, so prices went up considerably.

Best regards,
Mihailo
 
You gave me something to think about...

That's the reason for posting stuff like this :)

Here's the response of the whole system measured at 50cm mid ribbon with a 96kHz sampling rate.

Di3-right-50cm-midribbon-96kHz-response.png

-3dB at 21kHz and a very nice, clean roll-off without any spikes or resonances.
Here's the same measurement with the amplifier output of the tweeter amp pasted in:

Di3-right-50cm-midribbon-96kHz-both.png

The signal was measured at the NCore output as I did not dare to put alligator clips on the brass machine screws on the ribbon, if the clips snap off they will be pulled in the gap and the ribbon will be destroyed.
It's possible that the signal at the ribbon clamps is different, I will have to test this with my prototype ribbon when I have my test amp ready again.

regards,

Gerrit
 
Looks great! Definitely no resonances and very clean roll off. If i didn't know what you were building, I would say that's photoshoped. :)
Where is the crossover point, and what type of crossover do you use. (I assume 4th order)
I am still on the fence when it comes to choosing right type of ribbons. 1m tall quasi ribbon had great midrange and depth quality, but were too much directional. These shorter pure aluminium ones have faster response and clearer high frequencies. 30cm long ones have great upper midrange and good enough treble. Small and narrower ones (~10cm) have excellent treble and speed, are less directional, but need to be crossed over pretty high (~4-5kHz).
Every type has some qualities and problems. Probably combination of big quasi ribbon as midrange and small pure aluminium ones as tweeters would be the best, but then that's already made in better magnepan models.
What's your favourite type?
 
Looks great! Definitely no resonances and very clean roll off. If i didn't know what you were building, I would say that's photoshoped. :)
Where is the crossover point, and what type of crossover do you use. (I assume 4th order)
I am still on the fence when it comes to choosing right type of ribbons. 1m tall quasi ribbon had great midrange and depth quality, but were too much directional. These shorter pure aluminium ones have faster response and clearer high frequencies. 30cm long ones have great upper midrange and good enough treble. Small and narrower ones (~10cm) have excellent treble and speed, are less directional, but need to be crossed over pretty high (~4-5kHz).
Every type has some qualities and problems. Probably combination of big quasi ribbon as midrange and small pure aluminium ones as tweeters would be the best, but then that's already made in better magnepan models.
What's your favourite type?

Crossover is at 2.5kHz 24dB/oct LR. The response of the mid is a bit lower because it was measured mid-ribbon, measuring between the two results in a flat response but then there's more drop off at the top.
My first ribbon was 40cm long and 14mm wide, it is too directional and also very sensitive to draft. I have no experience with magneplanars other than the Neo10 so I cannot comment on that other than that the combination with the Neo10 works very well (Neo10 crossed at 400Hz).
You're absolutely correct that each type has it's pros and cons, for the time being I'll stick to small ribbons (10cm x 19mm or something like that) and will try to further optimise them. Applying foam wedges to increase vertical dispersion like they do at Raal is something I'd like to try. I really like the simplicity of a pure ribbon, the driving force acts on everything that moves and everything that moves is radiating sound.
The great thing about building tweeters is that you can measure them in a normal living room and get meaningful results.

regards,

Gerrit
 
Thanks for answer! 2,5kHz is great crossover point for that size of ribbon. I am too leaning on the small size of ribbons these days, but then the problem with integration between fast ribbon and slow mid/bass driver is heard. AMT speakers seem the obvious solution to radiating surface/ribbon surface area, but then again, they have much more complex movement and heavier membranes, which is heard in the end.
I never understood foam wedges, but i assume Alex did the measurements. I guess foam lets lower frequencies pass, while blocking upper ones. He works close to me, guess i should just call him someday and kindly ask for a visit. I'am ashamed to say I never heard his products. :(
I also started with 1m long ribbon, that was intended to have radiating surface near the apogee duetta/centaur speakers, which my friend had and I loved the sound of them. But that one plane in which I had to sit to hear music bothered me after a while.
I guess I have to get true measuring microphone first, because I am using just normal condenser mic in "diy look like measuring mic" housing.
I saw that you also don't use transformer for ribbon. What kind of efficiency/sensitivity are you getting?
 
Etching is interesting, but I must do that carefully in well ventilated area. Only problem is equally etching the foil to get to desired thickness. I can borrow micrometer to measure thickness exactly, but making 1m long foil must be difficult. I assume you can wrap the foil but probably is best to etch straight piece of foil. I will write down your cooking recipe, maybe I would have to do etching if I don't find already made foil.

Wima FKP3 capacitors appears to have structure that we need, but are very difficult to open because they are dipped in resin that is rock hard. (tried on wima mkp which is metalized foil). http://www.wima.com/EN/WIMA_FKP_3.pdf Need to find something similar.

Russian K40Y-9 could be useful.
 

Attachments

  • RussianPIO800.jpg
    RussianPIO800.jpg
    227.9 KB · Views: 713