Circular ribbon microphone capsule

[Arbolito]

Hello everyone,

I'm going to diy a ribbon microphone, and got the idea to buy arc shaped magnets instead of cilinder, to accomodate a round aluminium foil diaphragm, instead of the typical slice. Do you think this would work? Picture attached

I'm asking beforehand because I'm going on a tight budget and don't want to buy things that won't work

 

[soliloqueen]

If you have a 2d surface like this, it's called a planar magnetic driver and it has different properties than a linear ribbon. Uncommon (non-existent?) in microphones but popular in boutique headphones. I don't believe you can arrange the magnets and diaphragm this way and have it work efficiently. I'm not aware of any microphone that functions this way, despite how common it is in headphone drivers. More than likely, it's because it sucks somehow. Marik would probably know more about precisely why nobody does this. Not my area of expertise. The engineering is totally different than a ribbon. They function differently electrically and in the air, so engineering has diverged profoundly and high end planar and ribbon drivers barely resemble each other now, despite starting from this basic idea.

If you want to do this, I would suggest looking at some headphone drivers for inspiration on how to arrange the vents and magnets. Maybe find a cheap fostex set on eBay and take it apart.

 

[shabtek]

looks mechanically unstable

lower mass is a benefit

front to back path is longer; not desired in a conventional ribbon

where are the lines of flux in those curved magnets?
maybe they could be oriented in a novel way with a linear ribbon

 

[Arbolito]

interesting answers; what makes a round shape ideal for standard dynamic/condenser/else microphone diaphragms, but a rectangular shape is used in ribbons? Hard to find an answer on google

 

[Barry Hufker]

I'm not sure a circular shape is "ideal" for standard microphones. It is one approach. You'll find rectangular diaphragms from Milab. Products - Milab & Pearl Microphones
And triangular diaphragms from Ehrlund Ehrlund EHR-M

I like the idea you propose, but I think there is a need for refinement. Frankly, and I'm not the one to do it because I'm not clever enough, I'd love to see someone come up with a transducer that doesn't involve a diaphragm or ribbon...

 

[k brown]

I'm not sure a circular shape is "ideal" for standard microphones. It is one approach. You'll find rectangular diaphragms from Milab. Products - Milab & Pearl Microphones
And triangular diaphragms from Ehrlund Ehrlund EHR-M

I like the idea you propose, but I think there is a need for refinement. Frankly, and I'm not the one to do it because I'm not clever enough, I'd love to see someone come up with a transducer that doesn't involve a diaphragm or ribbon...

Such as an inverse ionophone, perhaps?
https://massless.info/Mics.html

 

[Barry Hufker]

While I was aware of a plasma speaker, I hadn't heard of a plasma microphone until your link. Thank you! I don't know if it is plasma that is a new direction, but I'm confident something else is "out there" to be found... But again, I admire you're thinking differently.

 

[kingkorg]

Hello everyone,

I'm going to diy a ribbon microphone, and got the idea to buy arc shaped magnets instead of cilinder, to accomodate a round aluminium foil diaphragm, instead of the typical slice. Do you think this would work? Picture attached

I'm asking beforehand because I'm going on a tight budget and don't want to buy things that won't work

Have you made a ribbon before? I don't think that flaps would hold. Material is couple of microns thick, they would just fly around with first puff of air. You want least mass possible with these, that's why they are built as thin, light ribbons. All the extra mass would kill the high end, and unnecessarily boost low end, and low end is not something ribbons struggle with.

 

[k brown]

Have you made a ribbon before? I don't think that flaps would hold. Material is couple of microns thick, they would just fly around with first puff of air. You want least mass possible with these, that's why they are built as thin, light ribbons. All the extra mass would kill the high end, and unnecessarily boost low end, and low end is not something ribbons struggle with.

Even if it worked, I can't imagine what the advantage would be.

It wouldn't be anything like a planar transducer, just a ribbon with 'flaps' that would make it unstable, and probably prone to early failure.

 

[JohnnyM]

My instinct is that these two areas would just fold backwards.


I’m also assuming that the strength of the magnetic field in the very centre would be different than centrally at the top or bottom, as the distance from the magnet is further?

If you weren’t on a tight budget I’d say go for it and do the experiment for us, but if you need it to work as expected, maybe don’t.

 

[Latie]

Hello everyone,

I'm going to diy a ribbon microphone, and got the idea to buy arc shaped magnets instead of cilinder, to accomodate a round aluminium foil diaphragm, instead of the typical slice. Do you think this would work? Picture attached

I'm asking beforehand because I'm going on a tight budget and don't want to buy things that won't work

Sorry it looks counterintuitive for me.. just my impression: The condenser and standard dynamic capsules have "all their points" closest to (and evenly distributed with respect to) the clamping and transduction area with circular or quasi-circular shapes, presenting the best proportion and equality of transfer of movement captured to transduction. in a "ribbon mic", held at the ends, that is obtained with... a ribbon. - I don't see the point of your innovation. Try the most standard forms. copy! Again, just my thought. greetings! Have a good year, and a good mic

 

[soapfoot]

In addition to all the others said, my first reaction is that it risks becoming a “sail.”

In other words, the already-treacherous air blasts that represent the leading cause of ribbon death would have more surface area to catch them, leading the ribbon to tear itself apart at the termination “tabs” at the first sign of a plosive…

 

[ccaudle]

I'm going on a tight budget and don't want to buy things that won't work

Not compatible goals. Tight budget implies you should do something which is well proven and well understood.
A design which has no examples to guide you means you get to find all the pitfalls and quirks, so you should expect to build multiple prototypes to get to the point where you decide if it could be made to work with a little more effort, or is just a blind alley and should be abandoned.

 

[Arbolito]

thanks everyone for the very useful insights, I'll go with the standard design first, to me it had seen like intuitively a circle could yield better sonic results

 

[frans]

You might also have a look at the old Fostex printed ribbon microphones .. that don't have a ribbon strip, but a foil where a spiral "winding" is printed on.

 

[k brown]

You might also have a look at the old Fostex printed ribbon microphones .. that don't have a ribbon strip, but a foil where a spiral "winding" is printed on.

. . . not very DIY, though.

 

[soapfoot]

. . . not very DIY, though.

True, but what about seeing if you could unwind a metallized film capacitor, and experimenting with the metallized film in place of a ribbon?

Might be too high in mass to give good HF response, but could be educational as an experiment!

 

[AndTripp]

…to me it had seen like intuitively a circle could yield better sonic results

My understanding of circular capsules as compared to rectangular one(Pearl, Milab) is the uniformity in horizontal and vertical polar response.

In the case of the latter, I’ve found the Pearl ELM-C, for example, to be incredibly useful in orchestral recording scenarios where you find yourself attempting to mic a choir while reducing bleed from percussion, which typically lives closer in proximity to the microphone.

My instinct is that these two areas would just fold backwards.

View attachment 119550
I’m also assuming that the strength of the magnetic field in the very centre would be different than centrally at the top or bottom, as the distance from the magnet is further?

If you weren’t on a tight budget I’d say go for it and do the experiment for us, but if you need it to work as expected, maybe don’t.

My instinct here is that the figure 8 properties might be compromised without proper tensioning on those side flaps. The magnet would certainly help displace air particle movement around the ribbon element when fully off axis, but I would think that measurably less tension at those flaps would be a source of increased output (likely of the noise variety?)

 

[ElSmurf]

My 2 cents, and something soliloqueen alluded to : the ribbon in a ribbon mic uses the same principle as a guitar string. A thin, long piece of material tensioned between two points to create - or transduce - sound. The round diaphragm in a dynamic mic works like a loudspeaker in reverse, where a circular coil is held in place around a round magnet by a circular tensioned diaphragm. And the round diaphragm in a condenser works like a drum, where the diaphragm is concentrically tensioned around a ring to create - or transduce - sound. In all these cases, the parts that move with the sound waves are kept in place through tension, linear or concentric, in one or two dimensions.

Looks to me like your idea lies somewhere between a ribbon and a dynamic mic, but without taking the tension principles into account.

 

[Marik]

Hello everyone,

I'm going to diy a ribbon microphone, and got the idea to buy arc shaped magnets instead of cilinder, to accomodate a round aluminium foil diaphragm, instead of the typical slice. Do you think this would work? Picture attached

I'm asking beforehand because I'm going on a tight budget and don't want to buy things that won't work

To make a good and efficient ribbon motor we have to observe a few conditions:

1. In the air gap we need to maintain a strong, efficient, and uniform flux, so the magnets should be in quite a close proximity and in parallel to each other. We don't want to place them too close, as then the modern Neodymium magnets will saturate. On the other hand, with distance we loose the filed considerably.
2. Ribbon should be stable, with minimum torsion movements. In general, the best ribbon shape to get a good stability and efficiency (along with low impedance) is rectangular.
3. For a good top end response the front to back distances should be minimal (I posted on this some time ago in depth).
4. Low impedance (DCR).

Let's see what happens if we make proposed circled shape:

1. The rule of the field is 2:4, IOW, if we increase the distance in twice, the filed will decrease 4 times. The optimal distance is about .200"--.250" depending on the magnet size. What happens in the round one--the field in the farthest points will be very weak, producing almost no signal. Also, this is providing you will be able to find the magnets of that shape magnetized in a correct plane.

2. Any 'flaps' will increase mass (without actual reducing DCR) and torsion instability, which results in resonances and all kinds of distortions. This is besides obvious fact the DCR will be weird.

3. The round shape introduces considerable front to back distances. Say 1" round will translate into some 1.750" front to back (including magnets), which translates into -3dB @ 7.7kHz.

That is how the ribbons came to a present (rectangular) form when you optimize each of those parameters and put into a system all together. If you are on the budget I'd definitely suggest to go conventional way in this case.

Best, M

P.S. Somebody posted earlier--against of our intuition the top end is not affected by ribbon mass.