My new ribbon hybrid mic

Marik

Pro Microphone Design
Lady and Gentlemen,

Please let me introduce my new creature. The world first ribbon--omni hybrid microphone. Well, probably not the first--remember WE-Altec 639A, but in this configuration--first. The omni part is based on WM61 Panasonic capsule and schematics found in ECM8000 thread. The ribbon part built around neodymium 10mmx10mmx36mm magnets. For now I put it in an old EV enclosure. Later, I will probably do something else.
 

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Here is a close up of the ribbon capsule. The ribbon itself is made out of 1.5 micron aluminum foil.
 

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Never seen one of those before!

I'm very curious to hear your results with that one!

Will you keep us posted?
 
Very cool. Now add a remote box with a polarity reverse switch on the ribbon and a level control on the omni, and you have a completely variable multi-pattern mic. If you can add a pivot to turn the omni 90°, you have a complete M-S setup.
 
Harvey Gerst said:
Very cool. Now add a remote box with a polarity reverse switch on the ribbon and a level control on the omni, and you have a completely variable multi-pattern mic. If you can add a pivot to turn the omni 90°, you have a complete M-S setup.

An omni won't care which direction it points. While some suggest the use of an omni mid, that results, after the M/S matrix, in two virtual cardiods pointing directly to the sides.

For a more traditional M/S I'd recommend the use of a WM55A cardiod capsule for the mid. The relative gains of it and the ribbon must be closely matched.

Marik, you'll get a much stronger field across the ribbon if you complete the magnetic circuit around the outside of the magnets with a U shaped piece of highly permeable metal.


Bob
 
Thank you Gentlemen,

It is too early to say something about sound, as I just finished it and have not tryed in real situation yet. From the first tests (on my voice) I can tell that the output of the ribbon section is very hot. The overall sound is very special. I was comparing it to different mics, and definitely this one has very unique qualities. If someone has a ribbon mic, try it with ECM8000--you will get same effect.

<Very cool. Now add a remote box with a polarity reverse switch on the ribbon and a level control on the omni, and you have a completely variable multi-pattern mic. If you can add a pivot to turn the omni 90°, you have a complete M-S setup.>

Harvey,

My idea was to use the omni as a 'fill in' for HF roll off of the ribbon and nice cardioid pattern.
You got it! Yes, I made it for MS recording, however, I will be using THIS one as a mid, however, I made a third channel in my pre with the reverse polarity and independant level adjustments for different patterns.

<For a more traditional M/S I'd recommend the use of a WM55A cardiod capsule for the mid. The relative gains of it and the ribbon must be closely matched.>

For the Side I will be using whether another ribbon, or KK87 capsule based tube mic. When I use MS, usually I record mid and side on different channels, and then matrix them during mastering.

<Marik, you'll get a much stronger field across the ribbon if you complete the magnetic circuit around the outside of the magnets with a U shaped piece of highly permeable metal.>

I made this way for three reasons:

1) Simplicity of the construction
2) The magnets are pretty darn strong (I used N48 grade), and output is pretty hot, and won't get much higher with magnetic return circuit.
3) The thickness of this metal piece will increase lenght of signal path between front and rear and thus, will reduce high frequency cut off point.
 
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Marik said:

<Marik, you'll get a much stronger field across the ribbon if you complete the magnetic circuit around the outside of the magnets with a U shaped piece of highly permeable metal.>

I made this way for three reasons:

1) Simplicity of the construction
2) The magnets are pretty darn strong (I used N48 grade), and output is pretty hot, and won't get much higher with magnetic return circuit.
It will get a lot stronger with a return path. Consider that you have two gaps in series, that in which the ribbon resides and the other going around between the other poles of the pieces.

That is like having two resistors in series. The return path, being longer is of much higher "resistance" than the gap so that the drop in the field strength will be predominantly due to that return path. Think of it as a resistive divider.

3) The thickness of this metal piece will increase lenght of signal path between front and rear and thus, will reduce high frequency cut off point.
It need not be very thick at all to make a big difference. Actually, I'm rather surprised that you report it as hot. Those must be some intense magnets. :-)

Very nice job, BTW. I don't want you to think I am unimpressed, I just don't know how to shut off the engineer in me.


Bob
 
Arcanemethodes,

<It will get a lot stronger with a return path.....
It need not be very thick at all to make a big difference.>

In theory it sounds right. The magnetic gauss is a directly proprtional to the mic sensitivity. Today I finished a new mic found in the picture below. I made it using neodymium magnets in return path between iron bars. And you want to know something? It did not make much noticable difference. These neodymium magnets are amazingly strong. How many times I pinched my fingers to blood... It is probably my speculation, but I suspect that there is a saturation point where the gauss is no longer so important. Remember Lowther speakers--neodymium magnets, air gap brought to the minimum, but still, sensitivity is around 103db--many vintage alnico magnet speakers have that.
Actually, now I think I should have built it without these iron bars for sake of HF response. BTW, the high sensitivity besides of strong magnets is due to very light ribbon.

Yeah, it is already my sixth ribbon mic I built so far.
 

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Marik said:
Here is a close up of the ribbon capsule. The ribbon itself is made out of 1.5 micron aluminum foil.
Wow! Great job (as usual)! Where did you end up getting the 1.5 micron stuff?

I thought about getting one of those old busted EV ribbons and use the case for the ribbon in my Oktava. Last time I checked, one that didn't even work went on eBay for $125-$150. Where did you get yours?
 
Marik said:
Arcanemethodes,

<It will get a lot stronger with a return path.....
It need not be very thick at all to make a big difference.>

In theory it sounds right. The magnetic gauss is a directly proprtional to the mic sensitivity. Today I finished a new mic found in the picture below. I made it using neodymium magnets in return path between iron bars. And you want to know something? It did not make much noticable difference.

Marik, did you compare the sensitivity of the assembly you show with and without the return path? You are right that theory predicts a big difference and I can't think of a reason why theory would fail in this case. I'd sure like to understand, though.

To say it isn't different is to say that you can increase the width of the gap without any reduction in field strength and I don't understand a mechanism that would allow for that behavior.

I'm fairly new around here, have you explained before your source and method for making the ribbons?


Thanks,

Bob
 
<Marik, did you compare the sensitivity of the assembly you show with and without the return path?>

Naturlicht!
Yep, when once I used ceramics, it made a lot of difference, now--nope.

<To say it isn't different is to say that you can increase the width of the gap without any reduction in field strength and I don't understand a mechanism that would allow for that behavior.>

The gap width increase is square proportional to magnetic guass. That is probably the most I can say in this case. We need somebody here who understands in magnetism.

<Where did you end up getting the 1.5 micron stuff?
I thought about getting one of those old busted EV ribbons and use the case for the ribbon in my Oktava. Last time I checked, one that didn't even work went on eBay for $125-$150. Where did you get yours?>

Stephen Sank kindly sent me a little sheet of original RCA stuff. I have left for probably 2-3 more ribbons. I found a source in UK for 2.5 and even 0.6 micron. It is expensive to buy only one, and price break is for little quantities. If somebody wants to join me to buy, please let me know. Before I was using foil from old paper in oil caps. The thinnest I could find was 2.5 micron, which is still good.

Yeah Flatpicker, you bet. I got EV busted on ebay a couple years ago. It was around $120, I think.
 
How are you guys measuring the micron film... are you using a precision micrometer, and if so, which one? Thanks

PS... great thread. :)
 
<DJL How are you guys measuring the micron film... are you using a precision micrometer, and if so, which one? Thanks>

I am using usual micrometer, but stack 10 layers of foil and then divide the measurement by this number. I saw digital micrometers in jewelry supply stores with 1 micron resolution--pretty expensive stuff. You can also find the thickness of the aluminum foil from it's mass.
 
Wow, Marik, you continue to amaze me! A while back I tried to build a ribbon element, but it was no more than a proof of principle. You could hear the rattle, when the ribbon moved. But then again I just used ordinary aluminum foil found in the kitchen and a couple of reed magnets I bought to buid guitar pickups. The transformer was ultra-cheapo too.

I'm really amazed you managed to build a real usable ribbon microphone from scratch.
 
Marik said:
<DJL How are you guys measuring the micron film... are you using a precision micrometer, and if so, which one? Thanks>

I am using usual micrometer, but stack 10 layers of foil and then divide the measurement by this number. I saw digital micrometers in jewelry supply stores with 1 micron resolution--pretty expensive stuff. You can also find the thickness of the aluminum foil from it's mass.
Thank you Marik. :)
 
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