Ribbon Resonant Frequency Tunning/Tensioning - Ribbon Microphones

[abbey road d enfer]

I was thinking about this method, and would like to try it out.
Could you guys help me out on how to setp this.

So if I understood correctly, I should send a small audio signal directly to the ribbon, then where I connect the Oscilloscope probes? also to both sides of the ribbon? or to the mic output after the output transformer?

You need to send the generator's output to the 200r output via a large resistor (typically 100 k). The voltage across the 200r connection should be presented to one of the inputs, and the generator's output to the scope's horizontal input, and the scope must be used in X-Y mode
If you set the gen at 10V, you'll have only about 20mV across the mic, so the inputs must be set according to these very different voltages.
When the gen frequency differs from the ribbon resonant frequency, the graph is an inclined ellipse, the width of which is proportional to the difference. When the gen frequency is equal to the ribbon fequency, the graph is an inclined line.
You may want to google "Lissajous oscilloscope".

 

[Whoops]

You need to send the generator's output to the 200r output via a large resistor (typically 100 k). The voltage across the 200r connection should be presented to one of the inputs, and the generator's output to the scope's horizontal input, and the scope must be used in X-Y mode
If you set the gen at 10V, you'll have only about 20mV across the mic, so the inputs must be set according to these very different voltages.
When the gen frequency differs from the ribbon resonant frequency, the graph is an inclined ellipse, the width of which is proportional to the difference. When the gen frequency is equal to the ribbon fequency, the graph is an inclined line.
You may want to google "Lissajous oscilloscope".

Thank Abbey, I will search "Lissajous oscilloscope", learn a bit more and try to do it as you wrote

Thank you so much

 

[Tubetec]

Did you have any luck with the measurements Whoops?

Could REW be set up to measure the impedence and therefore the resonance of a ribbon motor ?
How would we go about creating a sound source to test the frequency response of a ribbon motor/transformer ?

 

[Tubetec]

I found an interesting and simple way to look at the transient response of microphones in the microphone engineering handbook , it involves creating a spark then looking at resulting impulse response,
in the example in the book they use a electrically generated spark but a simple click piezo lighter might do it.
Condenser and ribbon mics tend to have relatively low ringing after the fact ,a dynamic has oscillations and resonances that long outlive the original sound .

 

[abbey road d enfer]

Could REW be set up to measure the impedence and therefore the resonance of a ribbon motor ?

Indeed. The standard impedance measurement in REW produces both the modulus AND phase of impedance, so one has to look for max amplitude and zero-phase.

How would we go about creating a sound source to test the frequency response of a ribbon motor/transformer ?

Very difficult, because ribbon mics are velocity sensors, so the stimulus must be a constant-velocity source, which is much more difficult than a constant-pressure source.
One of the techniques use a long tube (several meters) with loudspeakers at each end working in tandem and a special treatment of the walls that minimize aerodynamic losses.
One could say almost rocket science.
There was a discussion on the micbuilders group. IIRC Les Watts was on it.

 

[abbey road d enfer]

I found an interesting and simple way to look at the transient response of microphones in the microphone engineering handbook , it involves creating a spark then looking at resulting impulse response,
in the example in the book they use a electrically generated spark but a simple click piezo lighter might do it.

Again there's been a long discussion on the micbuilders group.
Although the principle is sound, putting it in practice is more difficult.
It is true that it shows quite well the overshoots and oscillations, but those who have tried to deduce the frequency response from this transient response have been quite disappointed, mainly because of the very small LF energy that it produces.

 

[Tubetec]

Thanks for the links Abbey ,

Maybe an old plastic piezo motorola horn could be repurposed to better couple the spark to the ribbon motor .
A momentary short across a lead acid battery lets out a very sharp click the trouble is you dont want the vapourised metal splattering all over your ribbon motor .

 

[Whoops]

Did you have any luck with the measurements Whoops?

Not really unfortunately,
But I have some doubts that tunning or tensioning is precisely measured by most folks. I think most people just tension it by hand and by experience and don't measure it at all.

I found a nice video of Clarence Kane showing his ENAK operation,
you can see a ribbon installation were tension was not scientificaly tunned or measured.
I'm not saying that it's not important or that no one measures it. I understand that Royer does it and maybe some other people are equipped or have a method to do it. But I'm starting to think that most of the times it's not something really precise and if you have the experience you will install a ribbon by hand and end up in the same tunning "ballpark" (more or less) every-time, which is probably good enough.

Watch the video, it's really nice. Clarence Kane is 95 years old now, which makes him the most experience person installing ribbons in the World:

 

[soliloqueen]

Maybe it could be done by putting a speaker next to the ribbon playing the correct frequency, tightening and loosening the ribbon until it's vibrating the most?

 

[Whoops]

Maybe it could be done by putting a speaker next to the ribbon playing the correct frequency, tightening and loosening the ribbon until it's vibrating the most?

From my experience in installing ribbons you don't have much "tightening and loosening" before it breaks. when you tighten it the first time you are compressing the thin ribbon, you loose it again and the area that was tightened is weaker now...

In the ENAK video they don't seem to be doing any tunning at all...

It's a bit similar situation with the videos I posted on LDC capsule making,
different videos with people installing Diaphragms in LDC capsules and in none of them you see any tunning being made.

Seems in both cases "LDC capsules" and "Ribbons" tunning is made above all by "eyesight"

https://groupdiy.com/threads/making-a-ldc-capsule-videos.76391/

 

[Marik]

It's a bit similar situation with the videos I posted on LDC capsule making,
different videos with people installing Diaphragms in LDC capsules and in none of them you see any tunning being made.

Seems in both cases "LDC capsules" and "Ribbons" tunning is made above all by "eyesight"

Whoops,

I cannot talk for other companies, however, in our more expensive line of ribbon microphones we use a special slider, which allows a continuous tension adjustment, and then gets locked in that position. I don't see any other reliable way of tuning the ribbon with a more, or less precision. As I indicated earlier in this thread all our ribbons are tuned within +/-0.5Hz and do not require any special matching.

Best, Mark

 

[Marik]

Maybe it could be done by putting a speaker next to the ribbon playing the correct frequency, tightening and loosening the ribbon until it's vibrating the most?

Soliloqueen,

While it works very well with 'piston' corrugated ribbons, because of much more complex resonant modes it doesn't work well with the 'zig zag' corrugated ones.

Best, M

 

[Whoops]

Whoops,

I cannot talk for other companies, however, in our more expensive line of ribbon microphones we use a special slider, which allows a continuous tension adjustment, and then gets locked in that position. As I indicated earlier in this thread all our ribbons are tuned within +/-0.5Hz and do not require any special matching.

Best, Mark

Hi Mark, I don't doubt you at all and I know you make great microphones and that you are passionate in trying to achieve the best you can.

What I'm doubtful of is that other companies or other re-ribbon services use a "special slider" like the one you use. I think most people just do it by experience and "eyesight".
Saying this I don't mean it will not achieve good results, I think with enough experience you will consistently get in the "ballpark" (not +/-0.5Hz for sure) to make it work well enough for the application.

Please check the ENAK video I posted, I'm sure it's really interesting to you also.
I would love your comments on the ribbon install in the video

Thanks Mark

 

[Whoops]

Another nice video, this one from AEA, it has some talk about their tunning and show what seem to be sending a signal to the ribbon at 7m18s:

 

[Whoops]

Rode video, showing their tensioning jig,
Although I never liked their microphones (condenser) I'm always impressed when seeing Rode factory videos, they have impressive automated machines:

 

[Marik]

Hi Mark, I don't doubt you at all and I know you make great microphones and that you are passionate in trying to achieve the best you can.

What I'm doubtful of is that other companies or other re-ribbon services use a "special slider" like the one you use. I think most people just do it by experience and "eyesight".
Saying this I don't mean it will not achieve good results, I think with enough experience you will consistently get in the "ballpark" (not +/-0.5Hz for sure) to make it work well enough for the application.

Please check the ENAK video I posted, I'm sure it's really interesting to you also.
I would love your comments on the ribbon install in the video

Thanks Mark

Whoops,

There is a big difference between manufacturers and re-ribbon services, which are always stuck with a given design. Especially with vintage ribbons there is not even close concept to what we call 'tolerances'. For example, out of a dozen of RCA77 you won't be able to find even a single matched pair, even in one single pattern--they are all over the place, everything is very loose, etc.

When a person does it all the time whole his life (like Clarence, for example) of course, he will be getting at the correct ballpark MOST of the time. With lose tolerances of the vintage ribbons that would be probably perfectly fine for the purpose. One thing to mention (since he shows in the video B&O ribbon mics) as far as I know he does those with conventional corrugation, instead of original 'piston' one. While for somebody it sounds OK, those who know original sonics of those mics will tell that it completely changes the sound, flavor, and specs.

Best, M

 

[Whoops]

Thanks for your explanations and input Mark.

 

[ccaudle]

conventional corrugation, instead of original 'piston' one

Is what you call "conventional" corrugation what you get from using gears to corrugate?
What are you referring to as "piston" corrugation? In an earlier post above you referred to "zig zag" corrugation; is "zig zag" also the same as conventional, or gear corrugated? Or is zig zag a third style?

 

[Tubetec]

The big old BBC ribbon mic has a ribbon tensioner arrangement also .

I guess it more a 'set and forget' type thing , where after the ribbon has been clamped any attempt to adjust it will most likely result in destruction .

I think the alignment of the ribbon in the gap is do-able by eye ,assuming good tollerances in the cutting of the ribbon itself and some practice . Its not something you want to be poking with feeler gauges in any case .

Pistonic ribbons Id like to learn more about and Im sure the BBC archives will shed plenty of light on the subject . I did try making a ribbon for a Beyer M-130 once from cigarette packet alu foil that I had removed the paper from reverse side , because the foil itself is embossed it was very fragile , the experiment was a failure in the end .

Zig-zag /corrugated , same thing , gear wheels etc
Pistonic is where the ribbon is formed with a rigid structure in the middle , towards the edges there are a few corrugations so the main part of the ribbon moves pistonically in the gap , a corrugated ribbon tends to move in a slightly wobbly way which results in resonances and overshoot /decay artifacts on transients .

I'm just about to get stuck into the BBC ribbon microphones documentation after my coffee ,
The great thing about the BBC docs is the plain language explanations of every aspect of the design/opperation of their stuff , but also including other companies products that they incorporated into their equipment schedual. The Beyer M160 looks like a good place to start to learn more about the pistonic ribbon .

http://www.bbceng.info/ti/non-eqpt/TI_S2_Microphones.pdf
page 114

below is the internal BBC test report on the Beyer M160 that Maric listed , Im just getting into it now ,but it seems to detail methods of frequency response measurements , above 200 hz ,free field room responce ,
and traveling wave tube below 200 hz .

http://downloads.bbc.co.uk/rd/pubs/reports/1965-32.pdf

 

[kaltavilla]

Rode video, showing their tensioning jig,
Although I never liked their microphones (condenser) I'm always impressed when seeing Rode factory videos, they have impressive automated machines:

The rode technique of using a finely tuned tensioning jig requires that some engineer has already figured that a particular tension setting will result in the ribbon motor ,once mounted, will exhibit a particular resonant frequency. In the video they are not showing how they came up with THAT particular tension setting. No secrets being divulged here.

The old school way that I learned of was that the resonant freq should be below the threshold of hearing, and has typically been between 8 and 12 Hz. Unless you have a speaker that can produce those freq's and can use that as a source (which they di NOT have in the 30's, the easiest thing is to take a small 2 or 4 bladed fan connected to a slow variable speed motor, and adjust the speed so that pulses of air being produced are at a rate that is within the desired frequency. With one end of the ribbon fixed and attached to a meter, put the free end of the ribbon onto the other end of the meter, and while the ribbon is being put in motion by the fan or speaker pulses, adjust tension until max voltage is read on the meter, then clamp down,

Not even close to rocket science. And, I'm going to get all philosophical about things now, so gloriously analog a method that it really should be the only way ribbons are allowed to be made. Plus you need a human being and their hands involved to complete the process. Skilled labor, I think they call it. How appropriate that a technique that requires 'feel' should be involved in making a device that captures how sound 'feels'.