DIY Graphene/Graphite diaphragm condenser capsule project

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frobozz

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Mar 12, 2021
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Hi, I am experimenting with condenser capsules. Having a small machine for tensioning the diaphragms, I am searching for a fast way to build the conductive membrane and I would like to share the process.
The idea (internet inspired) is to use conductive graphite deposited on the mylar membrane, since I don't have (yet) a vacuum machine for metal vapour deposition.
I bought:
Graphite spray (20 Euro)
20 meters 4 micron of expensive Mylar (40 Euro!) in Europe
Cheap Chinese K47 clone capsule ( it is not a good idea to dismount an original Neumann K47 ... :)) )
I already had the ring for tensioning the Mylar, but you can build one with a good SLA 3d printer or ask me for one of these rings (see picture)

In brief, the Mylar is mounted on the tensioning ring and next protected with a plastic ring exposing only the part of mylar that must be covered with graphite, then sprayed.
Second the Mylar is tensioned at desired resonance frequency.
In the end the Mylar is fastened and screwed in the donor K47 body. Measured with my capacimeter I got 120pF (the original Chinese K47 was 100pF on my capacimenter)
When tested, the sound lacks a bit of low frequencies, but it is very clear on high, no sibilant no resonances.
Any suggestion for improving the low frequencies?
Thank you for your attention!
 

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frobozz

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I tensioned using a resonance frequency of 1Khz on the membrane, maybe too much for this material or maybe the tension grows up when the diaphragm is fastened to the brass support. The deposition is very light but I don't know how it can influence the tension. I'll make one on 800hz and one on 600hz lets see..
 

frobozz

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Could be the spray itself is stiffening the Mylar?
This can be a good reason, but the layer is almost transparent... but I dont have a micrometer to measure its thickness. If this is the reason, trying relaxing the tension I guess will have no effect. I'll try next days
 

Icantthinkofaname

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Hope you get the low end figured out. I've got one of the K47s from WGT Center (so the RK47 I think), I wouldn't mind reskinning with graphite.

How's the high end compared to the usual Chinese K47?
 

Khron

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I have a few chinese capsules that could use some deburring of the backplates - no idea whether the diaphragms are glued to the rings or not though. But if this was a way to have a backup "way out", it'd be swell (y)
 

frobozz

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Hope you get the low end figured out. I've got one of the K47s from WGT Center (so the RK47 I think), I wouldn't mind reskinning with graphite.

How's the high end compared to the usual Chinese K47?
In my ears the sound is better thank Rk47 in high frequency. I will make a band pass test in the afternoon and publish results
 

frobozz

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Here the test results in my home made test box with one of my microphones. It is a a test box good enough to compare the capsules.in Blue the KK47 china and in purple the graphene I made. Both have that lack of basses I could hear clearly, and the graphene is more linear in high frequency: my ear was right! :)
 

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ZHAOMENG

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china
Using spraying to achieve the degree of conduction will deposit too thick graphite, because the evaporation of gold plating is only 20nm, this thickness will not affect the softness of the film, but your graphite engineering is too thick, and it will be harder after drying
 

ZHAOMENG

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Also, your film tension adjusting tool is almost identical to the one I use to make the capsule, hahaha
 

frobozz

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Using spraying to achieve the degree of conduction will deposit too thick graphite, because the evaporation of gold plating is only 20nm, this thickness will not affect the softness of the film, but your graphite engineering is too thick, and it will be harder after drying
But both the response test and the acoustic test are better than these predicted adverse effect of the powder deposition … maybe the tension is not so badly affected. The few db lost in bass frequency are present even in the original capsule with gold, maybe the structure of the capsule itself can be poor in low freq?
 

mhelin

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Where can you get those tensioning rings? Only one I know weights 250 g and is used in weight lifting, it's the most I can lift :) I could 3D print a ring (what are good measurements btw?) using PETG and add enough 5g car tire weights to get the total 120 g weight needed. 3D print using metal must be expensive...
E: Found these 1/4 lb disc weight which are close:
 
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frobozz

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Hi I made the tensioning rings, if you want I have one kit available: write me directly.
The outer diameter of mine is 56 and the inner 45 but these are not critical.
 

Vac11

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Hi Frobozz,

thank you for your offer. Tension ring looks fantastic!!! Hope you will solve your "gold on mylar" needings ASAP....

Best

M.
 

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Tubetec

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I have heard of people repairing electrostatic speakers with mylar film and applying powdered graphite to the surface ,apparently the graphite particals bond to the mylar automatically .
Trouble is its a high resistivity coating where the usual gold has low resistance ,
Im not sure how that might effect the sound in a microphone , maybe the charge on the capsule wouldnt be repleneshed quickly enough .
 

frobozz

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I can state that the sound is very close to the "gold" version of the K47. I am trying to improve the technique of spraying the circular spot, but I haven't reached the perfecition yet, even if it works correctly even having a not very clear aspect on the borders
 

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Murdock

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Would also like to thank Frobozz for the tension ring. Works great!

Maybe we could organize some kind of groupbuy for different diaphragm material. Seems that most of the companies only sell in quantities.
 

frobozz

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Mar 12, 2021
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Italy
This is a good idea. i am experimenting a way to grow real Graphene on a platic diaphragm.
Graphene is different from Graphite spray that I used on the capsule I posted opening this thread.
Graphene has atomic dimensions, but at present my test are unsuccesfull. The 6um layer does not survive the teatment. But now... time for vacation, don't you think? :) Thank you all for your support.
 

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