A somewhat different Ribbon Microphone - issues?

Hi groupdiy'ers,

I'm considering a somewhat different ribbon microphone which looks like the image attached to this post. Hope it's clear what the idea is ... 

One of the thoughts in doing it in this way is that summing the input from the range of conductors will give a higher output. However, before venturing into actually buying the magnets and foil I'd appreciate if one of you who knows about the intricacies of ribbon microphones can say whether or not the signal will sum - and to what extent.

A comment to the attached imagemodel:

- Between the conductors there will be a mylar like film so that the microphone conductor+film is fully attached to the structure behind, i.e. it will be a "closed" or "vented" design à la a condenser omni microphone.

- The conductors may either be connected in parallel or in series (very low resistance or somewhat higher resistance).


??? ... would the signals in the various conductors sum or does something else happen?


Cheers & thanks for any insights you may have 

Jesper

Don't you expect phase shifts between the different transducers? (Especially at HF)

Hi RuudNL,

Thank for your question & yes, I would expect some phase shift between the  conductors  but as I write it's basically one membrane as the individual conductors are connected with a thin film. Also, it won't look exactly like what I've illustrated although close ...

What I hope to achieve by choosing a hopefully sensible diameter is something like this in terms of the HF frequency response (see attachment) combined with an - again hopefully - somewhat higher output.

And I'm just not quite sure how much the output increases in practice ..? Can I just "more or less" add the output from the various conductors or will something like phase shift or ?? cause the output to be lower?

Thanks again for replying 

Jesper

Where /how do the magnetic poles arrange?

Is the motor movement linear 'up and down' coupled to the hemisperic diaphragm?

Is it an array of convensional motors arranged in a circle?
If so consider the various interference patterns between elements when combined--phase issues do come to mind

I think the best thing to do is try it and see how it works and sounds.
Keep us posted about the results!

gentlevoice1 said:

One of the thoughts in doing it in this way is that summing the input from the range of conductors will give a higher output.
...

- The conductors may either be connected in parallel or in series (very low resistance or somewhat higher resistance).
??? ... would the signals in the various conductors sum or does something else happen?

Click to expand...

It is summing if you connect all of the ribbons in series, but then you have much higher source resistance, so will be forced to keep the transformer ratio down, so you won't get much benefit there for amount of complication. If you connect them in parallel then you get the source resistance down and can increase transformer ratio to get signal increase. Your main enemy will be inevitable loss in the clamps, so actual benefit won't be as large as the math might suggests.

gentlevoice1 said:

- Between the conductors there will be a mylar like film so that the microphone conductor+film is fully attached to the structure behind, i.e. it will be a "closed" or "vented" design à la a condenser omni microphone.

Click to expand...

You will need to corrugate the ribbon to be able to tune it to the low frequencies to make it work as a mass controlled system. Otherwise you get a "nice-n'-honky" type of sound. Also, to get a flat response in the mass controlled system you will need to load the back of that structure with acoustical labyrinth. Ideally, it should be of infinite length, or of finite length with very carefully matched acoustical impedance. Not the easiest task--believe me--RCA were trying to do it in their ribbon mics and never fully succeeded.

In principle, you could make it work as a resistant controlled system, but then we have such a low output that cannot afford to accept any additional losses...

Best, M

Jesper, I don't think you have thought this through.

How are the foil strips moving?  Up & down?  In and out?  Do the top & bottom domes move?  How?

Where are the magnetic flux lines?  Where are the magnet poles?

Are the foil strips cutting the flux lines when they move?  If they don't .. you have no output.

Hi Marik,

Thanks for replying to my questions here   

It is very helpful and your comments and suggestions cast some more light on what may be the challenges in such a design. As it is my aim in doing it in this way is to "let go" of the transformer by providing more output to a active circuitry. I remember that in one of your previous answers to me you said that the output of a ribbon microphone was about 2 mV (95 dB SPL I suppose) so by summing more ribbons I would hope to achieve an output that resembles a ½" condenser microphone ... However, as I read your reply there are other "challenges" to observe ... Fine to know up front!

Thanks also to shabtek & ruudNL for your comments and questions 

Best regards,

Jesper

Hi ricardo,

Jesper, I don't think you have thought this through.

How are the foil strips moving?  Up & down?  In and out?  Do the top & bottom domes move?  How?

Where are the magnetic flux lines?  Where are the magnet poles?

Are the foil strips cutting the flux lines when they move?  If they don't .. you have no output.[/quote

Thank you also for asking questions 

As it is I have simulated this concept in the FEMM 4.2 simulator (free) and the flux lines do go through the membrane conductors which go from the top to the bottom. The magnets are diametrically magnetized and potentially arranged alternately so that the magnetic field corresponds with alternating current directions (serial connection of conductors) or same direction (parallel connection). Membrane movement will be towards-and-away from the center of the hemisphere. Movement presumably will also be so small that the magnetic field is "close" to identical during movement. Bottom domes are fixed - so that the top and bottom parts constitute the structure of the microphone. However, as I mentioned above, it does not look exactly like the illustration shows.

My main issues have been/are what Marik has addressed in his reply - assuming that I haven't overlooked something (which realistically is less likely  :)

Cheers,

Jesper

Click to expand...

gentlevoice1 said:

The magnets are diametrically magnetized and potentially arranged alternately so that the magnetic field corresponds with alternating current directions (serial connection of conductors) or same direction (parallel connection). Membrane movement will be towards-and-away from the center of the hemisphere.

Click to expand...

I'll leave Marik to explain ribbon sensitivity to you but I still don't think you have a working system.

Can you sketch a horizontal cross section showing

• Magnets
• Their poles
• Flux lines from pole to pole
• Conductors and how they move.  (These will be small thin tangential rectangles in a horizontal cross section)
• Supporting Mylar film

gentlevoice1 said:

As it is my aim in doing it in this way is to "let go" of the transformer by providing more output to a active circuitry...

I remember that in one of your previous answers to me you said that the output of a ribbon microphone was about 2 mV

Click to expand...

Yes... assuming we have a 1:36 transformer. Let's see, if we are lucky (meaning you can make good low loss clamps) with large scale ribbon we can get 0.15Ω DCR (or for all practical purposes call it DCR). How many do you have? 10? But then we could do the same job with only 4 ribbons (90degrees apart)... but why? OK, say, we have 10--then you get only some 1.5Ω DCR (again, if we forget all the wiring losses). Not enough even to use with very low Rbb BJT's. Even then you will need to use a transformer. But on a practical level it is much easier to make a good 0.15Ω source transformer than 1.5Ω one.

All of that aside (indeed, all those things can be sorted out with a fair amount of careful thinking and compromises), as I mentioned earlier, the hardest part of the project will actually be (considering even RCA, with all their R&D money and genius of Harry Olson's magnitude had failed the task) acoustical part. The main problem as I see it, you probably won't get a good omni mic. I'd think, any true pressure SD would probably do much better, if anything, just because the directivity pattern of your mic would be way too weird...

Personally, I wouldn't go there as a first ribbon project... I understand, that this would be very educational, but then before tuckling it I'd suggest to make a good (or at least fair) sounding cardioid ribbon mic with a single ribbon, and then go from there. Then all that learning experience you can apply to this project.

Best, M

ricardo said:

gentlevoice1 said:

The magnets are diametrically magnetized and potentially arranged alternately so that the magnetic field corresponds with alternating current directions (serial connection of conductors) or same direction (parallel connection). Membrane movement will be towards-and-away from the center of the hemisphere.

Click to expand...

I'll leave Marik to explain ribbon sensitivity to you but I still don't think you have a working system.

Can you sketch a horizontal cross section showing

• Magnets
• Their poles
• Flux lines from pole to pole
• Conductors and how they move.  (These will be small thin tangential rectangles in a horizontal cross section)
• Supporting Mylar film

Click to expand...

Ricardo,

Our posts crossed... I just assumed and took for granted from the very beginning all of your right concerns are already solved... even then, there is still looong way to go... if anything, how to corrugate and tune a single ribbon and how to make a nice, secure, and low resistance clamp...

Best, M

Hi Marik & ricardo,

Hmmm ... I appreciate your comments and "reservations" ... very valid.

However, since I have misunderstood/misread Marik's previous PM to me about the output level of a ribbon microphone I think the output level will be too low for my purpose (at least at this point in time). The output level is not 2 mVs for a normal "raw" ribbon microphone but 2mVs/36 which is a very much different level. My mistake & apology  ???

So I'll leave it be at least for now but a thank you once again for for taking the time & effort to reply 

Jesper

While off the beaten path, check this out, and the link to the Bruno labs example.

http://groupdiy.com/index.php?topic=43507.0

Hi Doug,

Thanks for the link to another "unusual" Ribbon Microphone  I actually knew about this/these one(s), however, have considered doing it in a somewhat different way in order to get a directionality pattern both horisontally & vertically that was not too narrow or frequency  dependent. Yet, as written above I've now put in on hold as I happened to misread Marik's info on ribbon mic output levels  :-\

But thanks for linking,

Jesper

Antique take on multiple ribbon application:
http://xaudiaelektrik.blogspot.ru/2011/03/motm-shaftesbury-velodyne-supreme.html
http://www.xaudia.com/omnip/Mics/shaftesbury/GB460775A.pdf

*ok, already posted, but still