Ribbon Mic Dissection Pictures

[rodabod]

Thanks for the advice, Marik.

In return, I have an interesting mic for you guys to have a look at. It is the STC 4115, high performance commentators' microphone.

Here are some shots of the motor:









I am working on this mic at the moment. Strangely, it had electronics inside, as it was designed for use in aircraft too.

It still seemed quiet, thin, and noisy with a Beyer 200 Ohm ribbon transformer, so I will have to think about it.... Maybe the ribbon has too high resistance.... I doubt it though because it is very small. I guess the ribbon is ~2 - 3 microns thick. I will keep trying - I had a similar problem with another STC mic which magically started working after dismantling and re-assembling!

 

[SilverhammerNZ]

Hi Marik,

This prototype looks the same both sides, note the hole on the base plate in pic2, this is side two and can have a baffle attached. I think the ribbon is offset in the gap as well (fore & aft).

This being one of the prototypes I believe there are some differences to the production line model, certainly I'm told they have differences in specs.

Larry

 

[SilverhammerNZ]

Correction re above post:

The ribbon is central NOT offset in the Naked Eye. I have not actually seen the ribbon exposed, prefer to leave the grill on.

Larry

 

[Marik]

[quote author="rodabod"]

[/quote]

:shock: :shock: :shock:

One can only guess its top corner frequency :wink:

thin, and noisy with a Beyer 200 Ohm ribbon transformer, so I will have to think about it.... Maybe the ribbon has too high resistance.... I doubt it though because it is very small. I guess the ribbon is ~2 - 3 microns thick. I will keep trying - I had a similar problem with another STC mic which magically started working after dismantling and re-assembling!

I bet you, the contacts are contaminated. Clean them and everything should be OK. But first, try to tighten the clamps--might help.
Nice deep corrugation and good humbucking circuit.

[quote author="SilverhammerNZ"] Correction re above post:

The ribbon is central NOT offset in the Naked Eye. [/quote]

Yeah, it is better this way. It should not make much difference and makes the mic more symmetrical as for the sound of the mic back side. Besides, you don't have to pay royalties to Mr. Royer, who holds the patent.

Wonedering what is the purpose of tapered shape of the frame. Is it one of the ways to get around of one of the claims of aforementioned patent? :wink:

 

[BBob]

What do you think of the cool green color of Silverhammer's Naked Eye?

I'm presenting the long running dissection of the 77DX (with a second, perfect reference mic preserved, of course) at

http://microphonium.blogspot.com/

 

[andy_simpson]

I wonder whether those mics with 'wedge' shaped magnet or 'pole' pieces could be considered as HF horns? Like the beyer m160 plastic 'resonator'....?

Just a point of interest.....

Also, whilst on the subject of ribbons, myself & my mic design partner were experimenting with sign-writers silver leaf for ribbon element last week.....very very very delicate but excellent (and also delicate sounding) sound (if rather hard to corrugate!).....doesn't hold its corrugations very well though, as we had to actually fold & crease the stuff in order to get the corrugations to hold with any permanence.

BBob - if price & practicality were no object, what kind of ribbon mic would you build? ie. if you were comissioned to make the mother of all ribbons at any cost - funded by NASA, for example - what are the limits, in your view?

Andy

 

[rodabod]

Aluminium leaf can sound great with some microphones.

If I had all the money in the world to design a ribbon mic, I would give up and accept that the STC 4038 probably the best ever design.

Coles have released a new ribbon mic which looks absolutely excellent:



Seriously though, I think if I were designing a new ribbon mic (which I will do one day) then I would make it very high band-width which HF roll-off around 20KHz. This is not easy though.

 

[BBob]

I suppose the question is something like the "what would you do if you had lunch with a Neumann executive" type of question that you may have seen elsewhere.

http://proav.pubdyn.com/Tech_Apps/January2006WhatsNext.htm

is a link to an article talking about carbon nanotube ribbon microphones which may use technology from medical imaging transducers now under development. The ultimate would be to have unlimited money to spend on a team of scientists and musicians who would work together to develop, test and use a new class of recording instruments.

But will carbon nanotube ribbons be the ultimate? If history tells us anything, it is that there will always be room for improvement.

We already engineer and redesign every part of the mics, one at a time, over and over. Iterative development can be incremental, but it eventually pays off. Drag racing works in a similar way - lots of tweaks, improvements and a good understanding of how it all works together is probably the tried and true method of choice. There is no magic, just a lot of work.

Fortunately, it is the most fun ever!

Is that really the inside of the Coles 4040?

Stay tuned for more at http://microphonium.blogspot.com/
the latest will be the continued deep dive into the 77DX, with some measurements and side notes.

BBob

 

[Marik]

Roddy,

Thanks for the Coles. As always, it seems like a very thoughtfull design. Interesting enough, they stay with a short ribbon arrangement, which ensures a good vertical directivity and better immunity to twisting, torsional and lateral modes. The deeper (rather than thicker) magnets ensure a good and strong flux and small distortions with high ribbon excursions.

What is the thickness of the frame? Length and width of the ribbon?
It is not quite clear if it has any pole pieces?

[quote author="rodabod"]
Seriously though, I think if I were designing a new ribbon mic (which I will do one day) then I would make it very high band-width which HF roll-off around 20KHz. This is not easy though.[/quote]

Been there...

With right magnets it is not a problem to make such HF extention. The problem begins when along with that you want to maintain a good (or at least fair) sensitivity, and that's where contradiction of output/top corner frequency comes into its ugly play.
Indeed not easy. There is one way, though... :wink:

BBob,

Thanks for the 77DX. One can like its sound or not, but along with B, C, and D it was one of the most most advanced, most ingenious, most innovative, most elaborate, and most revolutionary ribbon mic design, ever made, despite to its limitations.

 

[BBob]

Marik

What do you think are the primary limitations?

On the complexity issue:do more parts mean more uncontrolled variables? And how about the user friendliness of the 77DX? I've seen people try to use that mic and fail, in my opinion, only because they totally misunderstood the controls and how to use them. What could RCA have done to make it more intuitiive?


bbob








http://microphonium.blogspot.com

 

[rodabod]

[quote author="Marik"]
Thanks for the Coles. As always, it seems like a very thoughtfull design. Interesting enough, they stay with a short ribbon arrangement, which ensures a good vertical directivity and better immunity to twisting, torsional and lateral modes. The deeper (rather than thicker) magnets ensure a good and strong flux and small distortions with high ribbon excursions.[/quote]

Yes, you can see where they have carried on with the 4038 design with that short, wide ribbon. The main difference here is the magnet assembly.

I'd like to know what thickness of ribbon they use with that short ribbon? I tried thicker ribbon with some shorter ribbon assemblies and it sounded boomy and resonant. I wonder if they use some thing like 1 or 1.5 micron material like in the original 4038...

What is the thickness of the frame? Length and width of the ribbon?
It is not quite clear if it has any pole pieces?

Ahh.... I stole the photo. I don't know.

[quote author="rodabod"]
Seriously though, I think if I were designing a new ribbon mic (which I will do one day) then I would make it very high band-width which HF roll-off around 20KHz. This is not easy though.

Been there...[/quote]

:razz: I know!

With right magnets it is not a problem to make such HF extention. The problem begins when along with that you want to maintain a good (or at least fair) sensitivity, and that's where contradiction of output/top corner frequency comes into its ugly play.
Indeed not easy. There is one way, though... :wink:

Yes, it is the big contradiction! I quite like how ribbon design has these fairly linear relationships - it makes design easier to understand.

So... There are some methods of extending HF. You obviously have a few things up your sleeve!

Marik, what do you think of the Beyer M160 (or M130) - have you ever tried one? The M160 has a nice HF extension. I really like the sound of this mic. I sometimes think it sounds more like a dynamic than most "classic" or "large geometery" ribbon microphones.

By the way, I received the Oktava / Electro Harmonix ribbon mic like the one you showed above. I did not realise how short each ribbon was... The original ribbon feels very thick - surely it is thicker than 3 microns?

I was thinking of maybe trying Aluminium leaf to see if I can improve the sound, but this may lead to the resistance of the motor being too high.... I can't run the ribbons in parallel as they are permanently connected together at the bottom (if I connected in parallel, then one ribbon would be out of phase). So, I may try the leaf first, and if there is noise or bass-loss then I can try 2.5 micron material...

I am a little slow with the ribbon mics because I am working on my DIY preamps at the moment!

Roddy

 

[Marik]

[quote author="BBob"]Marik

What do you think are the primary limitations?

On the complexity issue:do more parts mean more uncontrolled variables? And how about the user friendliness of the 77DX? I've seen people try to use that mic and fail, in my opinion, only because they totally misunderstood the controls and how to use them. What could RCA have done to make it more intuitiive?
[/quote]

As I see, there are three major limitations there:
1. Very dense protective silk, which is responsible for harsh and agressive sound (while you are there listen and measure the mic with it and without).
2. Narrow ribbon. While I can understand advantages, the main limitation is reduced LF response and less "natural" sound.
3. Although it has 3 polar patterns, the "true" and accurate one in fact is an omni, only. The other two are "kind of".

I am not familiar with "user friendliness" of this mic, so its hard to comment on it, but one of the reasons I could imagine, might be in either limitation I mentioned above.
To be completly honest, I believe the 77A was the best in the vari pattern mics of the 77 RCA family, mostly due to pure electrical rather than acoustical pattern control. On the other way this mic is way to scarce, though, and one could just wonder why they stopped its producing (well... ir is a,most twice as big). I had it ones for quater an hour to play with. In my opinion it beats socks off the DX. I might be wrong, though... Was checking with unfamiliar setup.

 

[Marik]

[quote author="rodabod"]
...I tried thicker ribbon with some shorter ribbon assemblies and it sounded boomy and resonant. I wonder if they use some thing like 1 or 1.5 micron material like in the original 4038....[/quote]

The original was with 0.6um. With right damping makes a big difference.

Ahh.... I stole the photo.

Liar... I mean thief... Anyway cool!!! :razz:

Marik, what do you think of the Beyer M160 (or M130) - have you ever tried one? The M160 has a nice HF extension. I really like the sound of this mic. I sometimes think it sounds more like a dynamic than most "classic" or "large geometery" ribbon microphones..

Those guys are double ribbons. I made ones (and dropped the idea) this arrangement. I think I even posted about it here... somewhere...
Even though it had much more extended high frequencies, to me it did not sound as natural as a single ribbon.
Yes, I own the M160. It is OK, but I don't find much use for it... for the same reason. Have to admit, the more narrow (as Beyers) ribbons sound better in this arrangement.

By the way, I received the Oktava / Electro Harmonix ribbon mic like the one you showed above. I did not realise how short each ribbon was... The original ribbon feels very thick - surely it is thicker than 3 microns?.

Thats what I feel and what my digital micrometer says. Never meausred it right (i.e. weight vs. area).

I was thinking of maybe trying Aluminium leaf to see if I can improve the sound, but this may lead to the resistance of the motor being too high.... I can't run the ribbons in parallel as they are permanently connected together at the bottom (if I connected in parallel, then one ribbon would be out of phase). So, I may try the leaf first, and if there is noise or bass-loss then I can try 2.5 micron material...

IMO, most likely the leaf would be waste of time and effort with this mic.
I do it with 1.8um and barely make it, meaning... the bass is still in focus, but benefits from higher loads, if you know what I mean.

 

[rodabod]

[quote author="Marik"]
The original was with 0.6um. With right damping makes a big difference.[/quote]

Yes, damping can help avoid boomy resonance - you can see this in quite a few ribbon mics (tight steel mesh across the gap, near the ribbon).

Still, I wonder if it is as good as having thinner foil. I tried the "piston" method of having three or four corrugations at each end with a flat (slightly curved) centre to get rid of resonance, but it still sounded crap. I will need to experiment more...

Liar... I mean thief... Anyway cool!!! :razz:

Look here:

http://www.saturn-sound.com/find.htm

Yes, I own the M160. It is OK, but I don't find much use for it... for the same reason. Have to admit, the more narrow (as Beyers) ribbons sound better in this arrangement.

Have you tried the M160 on piano? How about te original M260? I had them on piano recently and it was really nice. They are single-ribbon,but I actually think the M160 is more accurate sounding. The M260 has a fairly soft sound which reminds me of larger ribbon mics.

IMO, most likely the leaf would be waste of time and effort with this mic.
I do it with 1.8um and barely make it, meaning... the bass is still in focus, but benefits from higher loads, if you know what I mean.

I agree - in the spec sheet it says that the impedance of the mic is around 600 Ohms + <120 Ohms.... This obviously needs a high impedance load to keep the bass happy.

If I fitted Aluminium leaf which is ~ 3 times thinner, then it would probably be terrible.

I might try a different transformer, but the motor already looks a bit crude, and I am not sure if it would be worth it. The frequency-response graph looks frightening! :razz:

I may see if I can run the motor without the two drilled plates on each side to see if it sounds any better.... I don't like the look of it just now with the cavity in-between the plates and those small holes. I realise that this is probably forming an MRC and gives strength, but I will see how the sound changes in case I can modify the plates.

 

[BBob]

Marik

Which digital micrometer do you have that measures in microns? What is your resolution, and accuracy? Do you use Jo blocks to calibrate?

bbob








http://microphonium.blogspot.com

 

[Marik]

[quote author="rodabod"]
Have you tried the M160 on piano? How about te original M260? I had them on piano recently and it was really nice. They are single-ribbon,but I actually think the M160 is more accurate sounding. The M260 has a fairly soft sound which reminds me of larger ribbon mics.
[/quote]

The problem is I record a classical piano with a distant miking, so since the output is quite low to start with, I have noise problems and whenever use ribbons always prefer higher output ones.

[quote author="BBob"]
Which digital micrometer do you have that measures in microns? What is your resolution, and accuracy? Do you use Jo blocks to calibrate?
[/quote]

I have a Mitutoyo with 1um resolution. By no means it is an accurate way, but it gives you a ballpark. The only correct way to measure those thicknesses is to weigh the foil and calculate from its area.

 

[CJ]

If you ribbon freaks still want a gaussmeter project, DIY style, let me know.

 

[BBob]

I'll bite. After spending too much on a couple of gaussmeters, I wouldn't mind looking into making some here. I did find a couple of metering schematics for use with the digikey Hall effect devices and I think we know how to calibrate.

What I'd really like is a way to visualize the magnetic field in 3D.

BTW, I have a pretty rare Charles Fisher (Cambridge Microphones) ribbon mic in the lab now. It is clearly a hand-made item but very interesting. We'll be giving it a new ribbon, and measuring the field along that unusual tapered gap. I will have more pictures later but I have one close up shot on the blog now. Youcan click on the posted image to get a higher res image if you want.

Bbob






http://microphonium.blogspot.com

 

[CJ]

http://my.execpc.com/~rhoadley/gallery/imageset.html

 

[rodabod]

[quote author="BBob"]
BTW, I have a pretty rare Charles Fisher (Cambridge Microphones) ribbon mic in the lab now. It is clearly a hand-made item but very interesting. We'll be giving it a new ribbon, and measuring the field along that unusual tapered gap. [/quote]

BBob, this microphone is interesting. I it would be nice if we could discuss it, because I was thinking about how a tapered pole-piece design would work.

I assume it will be a compromise between the HF roll-off of the thin and thicker pieces....

Also, will there be less magnetic flux at the thinner end of the pole-pieces?

And finally(!) am I correct in thinking that the ribbon width varies too?

Regards,

Roddy