Capsule reskinned with a birthday balloon

[jtmotenz]

Yes, the title is correct. Does it work? No.
But I am calling today a win because now I generally know how to do this. I achieved the critical gap in between the membrane and the backplate, and the tension is close enough compared to my other capsules.
Now I want to build a rig that will let me get the same exact tension, every time, and keep things perfectly aligned throughout the whole process.

I understand that the balloon is wayyyy too thick and not even close to being the right material, but it's all I had laying around. Baby steps.
I used a few large sockets and duct tape to secure the backplate, and a thin cylinder that I covered with the balloon material, tensioned by duct tape once again. I then put the cylinder over the backplate, and used more duct tape to pull the cylinder over the backplate contraption, allowing me to keep constant tension on the membrane.

Oh and I did the unforgivable mistake of puncturing the membrane with a screwdriver... This is why I'm using a balloon and not gold sputtered mylar.

Now I have to find some suitable membrane material and see if this would even work!

ps- I wired it up into a mic, and it responds to wind and taps onto the mic body. I suspect this is only because of the thickness of the balloon material. I think if it was the proper thickness, it would be audible despite only being aluminum... Any thoughts?

 

[k brown]

Actually the balloon is exactly the right material; they are Mylar, the same used in microphones - it's just, as you say, too thick and the aluminization probably also too heavy.

I don't know if it's just me, but I can't get your images to open.

 

[jarvis]

It's kind of hard to tell from the pictures but it looks you are shorting the diaphragm to the backplate. These center terminated capsules usually don't have any metal sputtered where the clamping ring is making contact with the diaphragm to provide isolation. With how you have it set up, it seems like the clamping ring is making direct contact with the sputtered aluminium and shorting it to the backplate via the screws.

Best
Jannis

 

[OneRoomStudio]

It's kind of hard to tell from the pictures but it looks you are shorting the diaphragm to the backplate. These center terminated capsules usually don't have any metal sputtered where the clamping ring is making contact with the diaphragm to provide isolation. With how you have it set up, it seems like the clamping ring is making direct contact with the sputtered aluminium and shorting it to the backplate via the screws.

Best
Jannis

I had the same thought. You might be better off trying an edge-terminated style (you can use the same backplate).

 

[ricardo]

This is why I'm using a balloon and not gold sputtered mylar.

Now I have to find some suitable membrane material and see if this would even work!

Gold has to be sputtered onto pretensioned Mylar. If you don't do this, the gold will crack when you tension the Mylar and you WILL have intermittent & unreliable yuckiness.

Aluminium flashed Mylar is far more forgiving. Go to a model shop with a multimeter and check their Aluminised Mylar is flashed on only one side. Some products have the Aluminium sealed inside so no use to us.

https://micronwings.com/product/mylar-5-micron-aluminised/

This is useful only for edge terminated capsules of course.

I think there is a Neumann (?) youTube video which shows how they tension capsules consistently. If anyone knows where it is, please post. We used the same method at Calrec with slight different jigs.

 

[jtmotenz]

Actually the balloon is exactly the right material; they are Mylar, the same used in microphones - it's just, as you say, too thick and the aluminization probably also too heavy.

I don't know if it's just me, but I can't get your images to open.

It's kind of hard to tell from the pictures but it looks you are shorting the diaphragm to the backplate. These center terminated capsules usually don't have any metal sputtered where the clamping ring is making contact with the diaphragm to provide isolation. With how you have it set up, it seems like the clamping ring is making direct contact with the sputtered aluminium and shorting it to the backplate via the screws.

Best
Jannis

You are correct. This was only a test. I can imagine that It will be hard to get mylar with the sputtering in a focused spot, so maybe I'll have to go with an edge terminated design.

 

[jtmotenz]

Gold has to be sputtered onto pretensioned Mylar. If you don't do this, the gold will crack when you tension the Mylar and you WILL have intermittent & unreliable yuckiness.

Aluminium flashed Mylar is far more forgiving. Go to a model shop with a multimeter and check their Aluminised Mylar is flashed on only one side. Some products have the Aluminium sealed inside so no use to us.

https://micronwings.com/product/mylar-5-micron-aluminised/

This is useful only for edge terminated capsules of course.

I think there is a Neumann (?) youTube video which shows how they tension capsules consistently. If anyone knows where it is, please post. We used the same method at Calrec with slight different jigs.

Thank you. Now how does aluminum perform? It's far less conductive obviously, at what point does this affect the sound?

 

[k brown]

Many fine microphones have aluminized diaphragms; for example, the Oktava MK-012 and the Line Audio Omni1 and CM4.

 

[gyraf]

..you can just remove the aluminum from the area you want without'it. Caustic soda? Some acid?

also, foil from unwinding axial polyester capacitors works, if the foil gets wide enough - i.e. if the axial cap started out long enough. Note that lower capacitor working voltage = thinner foil

 

[jtmotenz]

Many fine microphones have aluminized diaphragms; for example, the Oktava MK-012 and the Line Audio Omni1 and CM4.

Cool to hear, that was my next question.

 

[jtmotenz]

..you can just remove the aluminum from the area you want without'it. Caustic soda? Some acid?

also, foil from unwinding axial polyester capacitors works, if the foil gets wide enough - i.e. if the axial cap started out long enough. Note that lower capacitor working voltage = thinner foil

I've seen 47uF come up for this- maybe this is my next move.

 

[hank alrich]

I don't know if it's just me, but I can't get your images to open.

Same here. Previews look fine, but won't open into full picture.

 

[Khron]

I don't know if it's just me, but I can't get your images to open.

Same here. Previews look fine, but won't open into full picture.

Might need some waiting, the server's only got so much upload bandwidth, and three of the four photos are over 10MB in size; box-cutter one is "only" 1.5MB.

 

[RoadrunnerOZ]

For centre terminated the foil must not make contact with the outer ring/backplate, but also must make contact with the centre terminal -
1: is the foil being shorted at the outside periphery either via the screw holes or no insulator rings?
2: does the foil even make contact at the centre (or anywhere)? ie. is the aluminium an open conductive surface or sealed within the balloon material as a sandwich?
Easy to test with a meter if it’s shorting at the ring (and on a piece of scrap for surface conductivity).

 

[emrr]

I remember a blurb in an early 1930’s mag about keeping some chewing gum around because you might need the foil to re-skin your condenser mic in the field. Can’t say I ever read another mentioning a successful remote broadcast save! I found an ancient Wrigley’s wrapper that was used as book mark, much bigger than today and pure thin foil.

 

[pmfalcman]

..you can just remove the aluminum from the area you want without'it. Caustic soda? Some acid?

Yes. Caustic soda (NaOH) or hydrochloric acid (HCl) or sulfuric acid (H2SO4).

All are dangerous, highly corrosive and emit noxious fumes (and hydrogen) during reaction.
Although tiny area is to be cleared eye protection is a must and protecting gloves as a bare minimum.
Protective or old, disposable clothing is highly advised. Good ventillation too although we're talking quite minuscule amounts of bad emmisions.
These are extremely mischevious liquids (nasty litte bastards) and they always find a way to splash or at least drop themselves on something valuable. Eyes are the preferred target as well as favourite clothes or shoes.
Oh! And nice wooden tables! They just love them!
Super expensive exotic wood floors...

 

[jtmotenz]

For centre terminated the foil must not make contact with the outer ring/backplate, but also must make contact with the centre terminal -
1: is the foil being shorted at the outside periphery either via the screw holes or no insulator rings?
2: does the foil even make contact at the centre (or anywhere)? ie. is the aluminium an open conductive surface or sealed within the balloon material as a sandwich?
Easy to test with a meter if it’s shorting at the ring (and on a piece of scrap for surface conductivity).

So the requirement is that the diaphragm and the backplate must be insulated from each other regardless of the design (since they’re both charged with opposite polarity)…

Meaning for center terminated, you have a diaphragm that is insulated from the retaining ring, which terminates to the backplate via screws, right?

And for edge terminated, the retaining ring is conductive to the diaphragm, which means you’d need isolate BOTH the ring and diaphragm combo from the backplate… I’d imagine the screws are isolated then? Is there some kind of rubber on the backplate of these capsules that allows this insulation?

 

[RoadrunnerOZ]

So the requirement is that the diaphragm and the backplate must be insulated from each other regardless of the design (since they’re both charged with opposite polarity)…

Meaning for center terminated, you have a diaphragm that is insulated from the retaining ring, which terminates to the backplate via screws, right?

And for edge terminated, the retaining ring is conductive to the diaphragm, which means you’d need isolate BOTH the ring and diaphragm combo from the backplate… I’d imagine the screws are isolated then? Is there some kind of rubber on the backplate of these capsules that allows this insulation?

As for single diaphragm or dual diaphragm capsules no matter whether edge or centre terminated, the diaphragm is always insulated from the backplate - look at the components of the capsule you’ve dismantled and you will see the insulation method used - if the edge of the Mylar disk has no gold then there is no need for insulating ring washers, clearance holes for screws etc. as the outer periphery is non conductive - all electrical contact comes from the centre post and screw/washer - the post itself will be isolated from the backplate.
Edit: or there will be a screw clearance hole in the Mylar and insulation washer above the terminal tag washer

In one of your photos you have the components laid out - one of the rings looks like plastic - I hope you tracked the order of disassembly. Check the ring compositions, inner diameter of the terminal ring vs the other rings and screw hole sizes in each ring to work out how it all connects and clears.