Suggestions for aluminium ribbon damping?
here are two pictures of my wide range ribbons. The ribbons are 70mm wide and made of 11um thick aluminium kitchen foil. Backing film is clear packing tape, because it happened to be thinner than 1mil Kapton tape.
Amplification is done by diy direct drive class A SE Mosfet amps and MiniDSP.
The question is about aluminium ribbon damping.
My limited experience is that pure aluminum has a lot of resonances and the best way to damp the resonances is to use plastic backing material and to divide the ribbon to narrow vertical slices.
However there are still annoying resonances in the upper midrange.
Based on internet info I have understood that Apogee Full Range speakers had 50mm wide pure aluminium midrange ribbons with about 15um foil thickness and without any Kapton backing? How did they manage to succeed with pure aluminium without severe resonances?
Is ordinary kitchen foil totally wrong alloy to be used in a ribbon transducer or should I try to treat it somehow e.g. annealing?
you might experiment with embossed bumps on your foil rather than folding the foil. you can make the bumps any size you like. You will need a sheet of perforated metal or plastic with the hole size and pattern you want for the foil. rubbing the foil over the perforated surface will generate bumps in the foil. Best regards Moray James.
Thanks for your reply Moray James.
Here are some samples of different style corrugations I have tried. Almost all are pure aluminium without any backing material.
The diamond pattern is closest to your suggestion of embossed bumps.
Maybe I should try diamond pattern with plastic film backing.
And yes, all the different corrugations sound different from each other.
I received a question about more detailed construction info.
So here are a couple more pictures.
The ribbon frame is made of 30mm square steel tube. Some horizontal structural braces are welded behind the frame.
The bottom baseplate is screwed to steel frame (steel tubes have welded nuts inside).
Neodymium magnets are 50mm x 25mm x 3mm. Magnets don't need any glue to hold in place.
Ribbon frame height is of course from floor to ceiling. :)
Any chance you could create a "Making a Ribbon Loudpseaker for Dummies" tutorial?
I have enthusiasm but, better, a friend with a factory that can makes lots of things.
He has tools, CNC devices, space, etc.
What we need is cookbook instructions/suggestions/etc/description of parts to buy (that are available)
I guess I should point out that my ribbons are pushing the limits of ribbon design. 70mm wide ribbon combined with reasonably priced neodymium magnets leads to low efficiency due to low magnetic flux density.
I have attached couple FEMM modelling pictures to show the low flux.
This doesn't matter in my active system with my listening levels.
Ribbon high pass filter is LR4 at 140Hz.
A more standard wide range ribbon design would be 50mm wide ribbon with 200Hz LR4 high pass filter. It has higher efficiency if built with the same magnets I'm using. (My previous ribbons were like that.)
And for anyone reading this thread, please feel free to criticize my opinions. I'm no expert in this area and I would love to learn more.
pink noise playback at low level will reveal any problem with ribbon resonances (use high pass filter for small and medium sized ribbons) ... even flat ribbons/magnetostatics are sometimes not free from this kind of distortion , a rattling sound , very easy to hear with pink noise
not if there is ANY kind of flat foil driver out there that can do pink noise (smaller bandwith like 1/3octave does not help) without distortion artifacts
by playing music most of this artifacts are masked if the transducer is well constructed
I think a precisely corrugated 1-strip ribbon (your ribbons are too much warped, locally and globally) of 20mm width in a homogenous field will not produce hearable distortions with pink noise applied , but the mechanical suspension at both ends can play a major role here
on the net you will find several sources for downloading of pink noise as a test signal , just make sure you get WAV file format
go here an look at what Apogee did with there ribbons...it a brace page 4...goodluck
Thanks Marveloudio for pointing out the pink noise test. I will definitely do that.
You also pointed out that precisely corrugated 1-strip ribbon shold be the way to go. I would love to learn how to succeed with that for the simple reason that 1-strip pure aluminium ribbon is easier to diy than multitrack Kapton backed ribbon.
Thanks Tyu for the Apogee ribbon replacement link. That instruction has two interesting details:
1: Correct ribbon tension
2. The use of a glued flexible plastic ribbon support close to center of the ribbon length
I would like to hear comments how much these two details affect to ribbon resonances?
Or are they there just to protect the ribbon from over excursion and prevent low frequency flutter that sometimes occurs when using low order HP crossover slopes?
You might find the following of interest.
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