Suggestions for aluminium ribbon damping?

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Adding resistors in series can present an easier load to the amplifier, but it also dissipates energy as heat instead of sound. You end up throwing away watts (energy/time). If you have watts to burn that's fine. If not, maybe there are more elegant solutions.

The studies I've seen suggest that ribbon corrugations don't improve harmonic distortion performance. Of course some say harmonic distortion isn't a meaningful indicator of speaker performance so you can decide for yourself whether that information is useful.

I would expect that damping the *ends* of a ribbon would reduce the magnitude of its low frequency resonances but would likely have less effect on the higher frequency ones---the ones you're most likely to hear with the suggested pink noise test. Using felt to control resonances will probably have more effect at low rather than high frequencies as well. I think other approaches will be more effective if you have "crinkling" sounds to eliminate.

Few
 
Thanks for all tips guys. Based on the replies, I started thinking that maybe my ribbons are too wide. The idea behind my 70mm wide ribbons was to get some bass extension.
Now I'm a bit more experienced and I know that narrow ribbons without a wide baffle are no real bass transducers.

So I brought back my 40mm wide ribbons. The side by side comparison with 70mm ribbons showed that 40mm wide had more pleasant sound (both foil only ribbons).

Then I started experimenting with adding series resistor with 40mm wide ribbon. I added 0.1Ohm at a time and the sound cleaned up the more I added resistance.
So maybe my SE amp was not so good after all. The simulations showed low distortion numbers, but I haven't done any real measurements. Or it might be so that speaker cable inductance had too big role with 0.2Ohm ribbon resistance. I don't really know.

With 1Ohm series resistor the sound was much more clear than before. The downside was that about 80% of amplifier power was lost to resistor and SPL was low. I realized that it's not possible to continue with class A SE amp anymore. So I wired up my Hypex UCD amp (the specs say 1Ohm load impedance is ok). Side by side comparison showed that UCD amp had different sound compared with class A amp. I couldn't agree with my self which one was better, because both amps needed a bit different ribbon equalization to sound more similar with each other.
Oh well, maybe it's time to order a pair of Hypex Ncore modules..
 
Adding resistors in series can present an easier load to the amplifier, but it also dissipates energy as heat instead of sound. You end up throwing away watts (energy/time). If you have watts to burn that's fine. If not, maybe there are more elegant solutions.

The studies I've seen suggest that ribbon corrugations don't improve harmonic distortion performance. Of course some say harmonic distortion isn't a meaningful indicator of speaker performance so you can decide for yourself whether that information is useful.

I would expect that damping the *ends* of a ribbon would reduce the magnitude of its low frequency resonances but would likely have less effect on the higher frequency ones---the ones you're most likely to hear with the suggested pink noise test. Using felt to control resonances will probably have more effect at low rather than high frequencies as well. I think other approaches will be more effective if you have "crinkling" sounds to eliminate.

Few
So can crossovers, even more so. Full range planars are the way to go for the easiest way to get the full range of music.Simple as well.:)
 
Thanks for all tips guys. Based on the replies, I started thinking that maybe my ribbons are too wide. The idea behind my 70mm wide ribbons was to get some bass extension.
Now I'm a bit more experienced and I know that narrow ribbons without a wide baffle are no real bass transducers.

So I brought back my 40mm wide ribbons. The side by side comparison with 70mm ribbons showed that 40mm wide had more pleasant sound (both foil only ribbons).

Then I started experimenting with adding series resistor with 40mm wide ribbon. I added 0.1Ohm at a time and the sound cleaned up the more I added resistance.
So maybe my SE amp was not so good after all. The simulations showed low distortion numbers, but I haven't done any real measurements. Or it might be so that speaker cable inductance had too big role with 0.2Ohm ribbon resistance. I don't really know.

With 1Ohm series resistor the sound was much more clear than before. The downside was that about 80% of amplifier power was lost to resistor and SPL was low. I realized that it's not possible to continue with class A SE amp anymore. So I wired up my Hypex UCD amp (the specs say 1Ohm load impedance is ok). Side by side comparison showed that UCD amp had different sound compared with class A amp. I couldn't agree with my self which one was better, because both amps needed a bit different ribbon equalization to sound more similar with each other.
Oh well, maybe it's time to order a pair of Hypex Ncore modules..
My receiver goes down to 4 ohms, and my full range planar has 3.7 ohm input +7 and 15 ohm inputs. The diaphragm on its own is 3.7 ohms which is OK.It is full range and is 16" x 37" in size.I have built A4 sized full range as well.I have various valve amps which have 4 ohm outputs and they drive my planars quite well. Using 12 um mylar and 3 mm aluminium tape has increased the sensitivity as well.A taught diaphragm certainly gets rid of funny noises.
 
Hello all,
I'm designing a new corrugation gear.
I'm aiming for more corrugations per cm than my current ribbons and more sinusoidal corrugation pattern. The present ones look like a triangle wave.
Picture below..

Any suggestions what to aim for?
 

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don't bother with corrugations especially if you want a full range speaker. I NEVER DID AND I am quite happy with my full range planars. Much more inclusive than ribbons. You don't need crossovers with full range. Which only waste sensitivity and need a lot of sorting out. I think ribbons are a waste of space. Still this is only my idea other people may disagree. Each to his own . But after years and many designs, I have come to this conclusion.
 
Ribbons ...

The only book currently available about

Ribbon Loudspeakers Theory & Construction
by Justus Verhagen (Author)

published by Audio Amateur Press - was $24.95 when first published ...

Other suggestion is to use Plastic Film Capacitor Aluminum Foil - Unroll a quality cap and get a life time supply !

Jim
 
Thanks Torroid88, I ordered the book.

I noticed that this company uses different corrugation style than Apogee (fewer corrugations per cm):
Mono and Stereo: Miro Krajnc SoulSonic Wave loudspeaker

And this link says they use 8um thick foil only ribbon:
http://1pekingroad.com/zaspx/replie...subjectno=1849&sortby=updatedate&orderby=desc

I have attached a picture of my 40mm wide / 11um thick ribbons that seem closer to Soulsonic corrugation style. They also have resonances that can be heard with pink noise test and seen in measured frequency response.

Any tips where to get 40mm wide and about 8um thick alu foil?
My foil/film capacitors that have 8um foil are only 10mm wide.
 

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While waiting for the book to arrive, I took frequency response measurements from left and right channel ribbons. Below are unequalized ribbon responses.
The measurement mic was 10cm distance from ribbon.
Anyone care to comment about the ~2kHz resonance?

My differently corrugated ribbons all have this kind of high Q resonance. Only the frequency and amplitude varies. Ribbon tension affects to the resonance frequency and amplitude.
 

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I think the resonance is caused by the cavity between the two rows of magnets. It is very much like the cavity resonance of the Carver ribbon drivers (that are not true ribbons). The Carver's resonate at a higher frequency 7-8 kHz as the slot is narrower.

How did you measure the frequency response? It seems to be made at a low SPL. Are they really going that low in the bass? That will require very large excursions of the ribbon at higher SPL and probably "polute" higher frequencies.

Roger
 
I tend to agree with Roger but I'm surprised that the frequency shifts when the ribbon characteristics are changed if the resonance is a characteristic of the magnet gap. How much does it change? Small shifts might be explicable in terms of changes in the cavity but if it shifts by KHz I may have to rethink my assertion that the magnet cavity is the culprit.
Few
 
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The measurements are made with Room EQ Wizard software and the microphone is according to instructions at Linkwitzlab. Such a great site!

The measurements were performed with low volume, mic was 10cm away from ribbon surface.
I have learned that narrow ribbon without a baffle can't produce the needed SPL at bass frequencies, so the equalized acoustic response is first order high pass filter at 200Hz. (I have also a steep high pass filter at 80Hz to remove the ribbon excursion)

I can make and post frequency response measurements with different corrugation styles.
That should tell if my problems are caused by cavity resonances or ribbon resonances
 
So here are two measurements (high pass filter used, measurement distance was 10cm). No other changes except ribbon tension is increased.
The normal tension measurement is performed with the pink noise test tuned ribbon tension.
And the max tension measurement is performed with even more increased tension so that the corrugations flatten out almost to a flat foil.

So it seems that the about 2KHz resonance is due to corrugation, not due to cavity resonances.
Another fact that supports this theory is that my ribbon headphones have exactly same phenomenon even though they have totally different construction and different materials.

Hopefully the book arrives soon and I will learn more..
 

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Here are some more measurements. These are from my ribbon headphones with 6um thick capacitor foil.
Measurement distance is 1cm away from ribbon surface.

Measurement graphs show the same phenomenon as my previous post. The more ribbon tension is increased, the more corrugations will be flattened and the resonance diminishes.
Graphs also show the ribbon fundamental resonance frequency that is under 20Hz.

I guess this proves that the resonance is due to corrugation?
 

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I am in the process of finishing a DIY Apogee (Duetta Signature) like speaker. Right now I am making a corrugator tool for the bass ribbon. I have got hold of 25um Kapton film and the Aluminium foil is the Danish type 9um thickness. (Paper backed with wax as the adhesive) I have the test procedure for some Apogee's. They are showing no such resonance?
Could this be taken care of by the passive crossover possibly? Can not attach the procedure PDF format here (too big). Those interested send me a PM and I will mail it to you.
 
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I have got hold of 25um Kapton film and the Aluminium foil is the Danish type 9um thickness. (Paper backed with wax as the adhesive) I have the test procedure for some Apogee's. They are showing no such resonance?
Could this be taken care of by the passive crossover possibly? Can not attach the procedure PDF format here (too big). Those interested send me a PM and I will mail it to you.

There are laminated foil too, 12µm polyester with 9µm aluminium. You will then remove the unwanted aluminium by etching.
 
There are laminated foil too, 12µm polyester with 9µm aluminium. You will then remove the unwanted aluminium by etching.

I´ll second Rogers suggestion. I used the mentioned method some 20+ years ago. If you know the exact thickness of your alu-foil then you can design the membrane so that you will get exactly the impedance you want. This is very nice since you are able to design the width of the aluminum so that it is exactly the same as your magnets.

When done properly (be very patient and careful!) you will get a very nice, even and smooth membrane without rattling at buzzing. Now comes the difficult part: Tensioning of the membrane. You need to construct a tensioning system at two of the sides so that you are able to get a perfectly smooth membrane which has exactly the "same tightness" in all four directions. This is easy if the area is a square or similar, but if two of the sides are not parallel (like in the Apogee types) this tightening procedure can be a little tricky - but not impossible at all.

Best wishes

Karsten

PS! If I remember correctly we etched the aluminum with a strong solution of NaOH. This was extremely hard to the lungs so please wear rubber gloves, safety-glasses and a filter-mask - and open windows :D. My HiFi-buddy dropped a little of the NaOH on his carpet and there was a big hole in it immediately :eek:
 
I will use the hand cutting method. Have done a prototype uncorrugated. Placing the sheet, aluminium side to aluminium side and draw the pattern on the paper backing. Cutting through both of them and taping with 3m tape afterwards to keep everything in place. I use diluted contact adhesive on both the Kapton and the aluminium side of the ready cut membrane. Afterwards I use White Spirit on the paper side of the membrane and after a few minutes the wax dissolves and the paper comes off quite easily. Clean away the rest of the wax with a soft cloth moistiured in White Spirit. Membrane ready.
Have to do a lot of test corrugations to adjust the lenght of the ready made corrugated membrane. That is, so I can stretch it to the correct size. The adjustable springs are ready waiting for the tensioning process.
 
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