Materials for pole pieces in ribbon mics

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> The multiple wires increase signal

They increase Voltage. But by having higher resistance, the available current is decreased. The Power stays the same. You can get the same effect with a transformer. You can trade voltage and current any way you need, but power is precious.

I doubt you can fit enough conductors to eliminate the transformer. As you as you need one anyway, it makes nearly no difference if it needs to be 1:5 or 1:40.

And bringing the circuits around to series the multiple conductors adds stray resistance and a lot of complication.

You want ONE conductor. You want a maximum area/mass ratio (super-thin). And you want almost all of the ribbon's mass to be conductive, to maximize the power output. And Aluminum has the best conductivity to mass ratio of any practical material. (Lithium is better but burns-up in air....)

Copper is almost twice as heavy for conductivity, and silver is heavier. Copper finds much use in wideband loudspeakers: speakers are often designed heavier than "necessary" to drop the midrage to fit the ends, so copper does not hurt, and copper is a lot easier to solder.

> an advantage to having a composite ribbon of some sort?

If you could add a damping-layer without adding much mass, that might be good. Strength is good when a mike is abused (though Al has excellent strength/mass ratio). Note that some very-fine mikes are just aluminum, so I'd suspect there is no simple "better" technique along these lines.

Loudspeakers are a little different. While you could build a big ribbon mike, the charm of the plan requires it to be smaller than a wavelength, an inch or so, if possible, to keep it neutral to high frequencies. But in a speaker, while small is good for dispersion, it is very bad for acoustic distortion and it is futile to make a teeny speaker. When scaled to many square inches, and 8Ω lines, zig-zagged conductors can make sense. (But count all the Magneplanars in your home and studio.... ribbon-principle loudspeakers have never caught-on.)
 
[quote author="Marik"]
The corrugated 2"x1/4" ribbon from a leaf (probably ~0.6um) has 0.85 Ohm, measured on my GenRad 1650A bridge. [/quote]
Yes, my ribbons (the some dimension, but may be thicker)
have 0,16 Ohms. Measured by four terminal method.
Olson have the some resistance :) :) :).

What method did use 1650 A ? am did you comparsion to 0.1
Ohm etalon.
It is hard to work correctly with small-resistancy measurement apparatus,
full of mercury ...
xvlk
 
about how to make thinner ribbon....

a lot of time ago happened to drop some etching solution over a little piece of common cooking aluminium foil. That became very thin and in some area it was quite transparent because etching produced very thin hole in it.

So, what about using a very diluted etching solution to thin the ribbon?


Alessio
 
PRR (Re: Whackamole's idea)-

I'm curious why you would still need a transformer with such a design. Seems to me that the ribbon itself would serve the same purpose, ie. increase voltage and impedance. Since you can control width, thickness and number of conductors, you should be able to have independent control of voltage and resistance. I see the elimination of the transformer as one of the major motivations to try a design like this.

Also, regarding damping, wouldn't you get some improvement here since mylar has much lower modulus than aluminum? Although, once the metal conductors are on top, this will certainly change.

This discussion is kind of funny because I've actually been working on a similar design for the past few months. I've been pulled off on other, more serious projects recently, but I made significant progress with respect to putting many fine conductors on mylar. I belive I have solved the issue of bringing the conductors around, but I'm curious as to what effect you think the "stray" resistance will have.

If I had another month or two to work on this, I could probably have a prototype ready. I have a couple pretty major manufacturing problems to overcome with respect to placing and securing the ribbon (working with this thin mylar is such a PITA!), but I'm almost there.....just wondering if it's really worth my time.
 
[quote author="Marik"]I don't think what you are proposing would work as it is impossible to corrugate a mylar. It just won't "remember" the shape. [/quote]

Actually, I think the Fostex mic has corrugation in the mylar. I have a pdf of the AES paper they published for these mics and it shows some different shapes they tried. If anybody wants this, PM me with your email. There is also an old patent by R. Gamzon that you can find if you search uspto.gov.

I've never heard the Fostex mic either, but the thing that bothers me about the design is that the shape of the diaphragm necessitates a lot of 'stuff' in the sound path. It seems to me that the simple geometry of a traditional ribbon mic is a huge part of the appeal. One of the goals I had in mind when working on my version of the printed ribbon was to retain that simple geometry - parallel magnets with the ribbon suspended in the field. Since mylar is more mechanically robust than thin aluminum, I think you could also make the ribbon width smaller, which will allow you to put the magnets closer together increasing B field and decreasing path length.

I'm still curious if you guys have more input on this.
 
I never heard the fostex mix either, but many people says fantastic things about it...

It´s called "printed" ribbon mic, so maybe it gives us some insight on how the corrugations are made :?: :? :?:
 
Here are a couple of pics..of the Ribbon mic you all want to buy ;-)

I very happy with the 2 I have..I totally dig them on Drums, Bass Guitar, Double bass..

http://img.photobucket.com/albums/v166/PSL-Design/HPIM1704.jpg

http://img.photobucket.com/albums/v166/PSL-Design/HPIM1702.jpg

http://img.photobucket.com/albums/v166/PSL-Design/HPIM1700.jpg

http://img.photobucket.com/albums/v166/PSL-Design/HPIM1697.jpg

http://img.photobucket.com/albums/v166/PSL-Design/HPIM1698.jpg

http://img.photobucket.com/albums/v166/PSL-Design/HPIM1696.jpg

http://img.photobucket.com/albums/v166/PSL-Design/HPIM1695.jpg

http://img.photobucket.com/albums/v166/PSL-Design/HPIM1693.jpg

As you can see..plenty off room for "improvements" if thats your thing :green: ...imho it pretty damm good as it is..I like the colour..a little ´ol school sounding from way back when..;-)

EDIT..!!! Sorry I just realized what a stupit Fu..!! I am..I wanted to post these pics under the "Cheap lolly pop & ribbon mics."

Sorry for this..;-)
Kind regards

Peter
 
This is an old thread, but here are some more findings:

[quote author="PRR"]
pole pieces are almost a waste of time. Hard drives, where the magnetic system is engineered to DEATH, no longer use pole-iron. It is no longer necessary to funnel-down the flux from a big hunk of Alnico or ferrite to a small pole; the magnet is a fine pole by itself.
[/quote]

I suspected that for a long time, but wanted to try it, anyway. Lately, I made some experiments, hoping that tapered pole pieces at least to some degree will concentrate flux of the 1.5"x0.5" Neo N48 surface. The flux dropped from 8000 Gauss across 0.25" gap (no pole pieces), to 5500 Gauss (with pole pieces). The similar drop I got with smaller magnets.

I changed old, weakened Alnicos in EV V-1 with N40 1"x1"x1.5" neodymiums. It uses long and wide mild steel poles, and magnet placed underneath the frame. I read just slightly higher flux in a gap.

It seems old ribbon microphones had highly inefficient magnet structures, where most of the flux energy got dissipated in iron.

There is such a thing as "too much" flux. Too much magnet on a cone woofer raises midrange and relatively reduces output around resonance, giving "soft bass". The same can happen in a ribbon: more bass and midrange, but the top octave gets a heavy mechanical resistance loading, especially with non-infinite electrical loading.

Luckily, it is impossible to get "too much flux" in ribbon microphone in a sensible way, without going into some crazy impractical magnet sizes. Calculations show that even getting 1T across 0.2" gap, requires 2"x0.8"x0.8" N48 magnets.

I love magnets. They are... unpredictable :evil:
 
marik do you add pole peices only?
OR
do you add a magnetic return circuit and pole peices?

if you add pole peices the distance between the actual magnets increases by the thickness of the pole peices ...
with air as a MRC magnets in close proximity may behave differently.. if...pole peices are added the "air" mrc will become less efficient ... correct?
so maybe if you add pole peice AND MRC flux will increase..
this would be very interesting to know.

and since you have all that cool equipment for testing .. i look forward to hear more of your results :grin:
it is nice to see ribbon mic discussions continue ...
thanks for the info ... this is some thing i have been experimenting with too ... (as you probably already know)

what are the measurements of your pole peices?

ALSO: remember the idea i had to use razor blade for pole peices?
just about 1-1.5mm and somehow attach razor to flat plate (another razor perhaps)
i can't figure out how to attach the 2 together ( 1mm x 50mm x 0.5mm pole peice and the 0.5mm x 5mm x 50mm plate)
my theory is that : decreased ditance with tiny pole peice AND MRC will be very efficient.

looking forward to your comments
later
ts
 
[quote author="ToobieSnack"]
ALSO: remember the idea i had to use razor blade for pole peices?
[/quote]

TS, that sounds interesting.

What is the idea behind chamfered pole pieces? Does it give more magnetic flux? (I know little about magnetism).

Also, would the ribbon not swing out of the magnetic field under high SPL?

On a side note, has anyone had a bash at making (or know the theory behind the operation of) a cardioid ribbon mic?

I would imagine you would just need some suitable venting to the back, but I'm not sure.
 
[quote author="ToobieSnack"]marik do you add pole peices only?
OR
do you add a magnetic return circuit and pole peices?

if you add pole peices the distance between the actual magnets increases by the thickness of the pole peices ...
with air as a MRC magnets in close proximity may behave differently.. if...pole peices are added the "air" mrc will become less efficient ... correct?
so maybe if you add pole peice AND MRC flux will increase..
this would be very interesting to know.[/quote]

I tried pole pieces only. I don't think the air works as a MRC at all in this context. There are many other factors, such as field cancellation because of close proximity of S and N of the magnet, which are much more predominant here.
Anyway, considering that with steel on back of the magnet increases the magnet energy by only about 20%, and closing the MRC path by another couple %%, the "air" effect will be negligible, if any.


ALSO: remember the idea i had to use razor blade for pole peices?
just about 1-1.5mm and somehow attach razor to flat plate (another razor perhaps)
i can't figure out how to attach the 2 together ( 1mm x 50mm x 0.5mm pole peice and the 0.5mm x 5mm x 50mm plate)
my theory is that : decreased ditance with tiny pole peice AND MRC will be very efficient.

Sorry, I don't recall it. I think such small pieces of metal might saturate very easily, reducing efficiency even further.

[quote author="rodabod"]

On a side note, has anyone had a bash at making (or know the theory behind the operation of) a cardioid ribbon mic?

I would imagine you would just need some suitable venting to the back, but I'm not sure.[/quote]

There are two ways of getting cardioid pattern in ribbon mics:

1) Electrically, combining pressure and velocity elements. This route went many cardioid RCA models, and hybrids like multipattern Altec/Western Electric 639, American DR330.

2) Acoustically, with the venting to the back, you are describing. This way built Shure, Beyer, Fostex printed ribbon cardioids, and use pretty heavy acoustical resistance.
The RCA 77D and DX are also went this way, but completely differently, having an elaborate labyrinth, as a back chamber acoustical loading.
 
xvlk .. i would love to see American DR330 drawings .. schematics ..

rbod .. i just try and succed or fail ... and take notes :wink: ,,,lol

later
ts
 

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