Diaphragm tensioning for a 34mm capsule?

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frobozz

Member
Joined
Mar 12, 2021
Messages
15
Location
Italy
Hi everybody, I found this machine I got many years ago from a friend, and I started investigating how these 34mm capsule are made. First Thank you to this wonderful forum and people posting here for all great suggestion I read ! But many questions still need an answer after I tried to Reskin a broken K78 with a simple Mylar from my kitchen (I don't know its thickness... I only wanted to check I could make it :) )
In the pictures you can see what I did. First I tightened the Mylar to the tensioning ring with its 6 screws,
Next I put the ring on the plate over the loudspeaker. I played a sinusoidal wave of 440Hz and turned the tensioning ring (a threaded ring pushing the mylar out of the plate allows tension adjusting) until I could clearly listen to a resonance in the diaphragm.
Next I put the tensioned Mylar and its ring on the capsule leaving the silver spacer under the mylar and screwed. Final cut and it is done. See pictures for reference.
But I have some questions:
1. I know that the tension of the Mylar affects the bandpass of the capsule, but the question is: in this K87 or in a K47 which is the right resonance frequency?
2. Is there any place where I can buy the Mylar already sputtered with gold? I have many broken diaphragms K47, K67,K87 in my lab and I would like to try Reskin by myself. (The sputtered Mylar you can see in the pictures is broken too)
Thank you in advance!
 

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soliloqueen

Well-known member
GDIY Supporter
Joined
Oct 5, 2020
Messages
234
generally they're tuned about 980hzish I think. Really all around 1khz in every direction depending on the manufacturer, but that's after the size decrease post-clamping. if you want to do it the rode way (with a speaker tuning) you may need to do some drumhead math to figure out what tuning in the jig will get you 980 on the final capsule
 

frobozz

Member
Joined
Mar 12, 2021
Messages
15
Location
Italy
Thank you for your answer! I got the point. Some additional test are needed because the tension will be different after the new Mylar is fastened to the capsule and cut.

Any chance to buy the Mylar with sputtered gold for 34mm capsules?

Please help :)
 

rmburrow

Well-known member
Joined
Oct 8, 2013
Messages
199
Sputtered gold on Mylar is hard to get and expensive to make. I use 1 micron nickel. Somewhat harder to work with but stable once in place. Tolerates tension. Be careful, depending on the manufacturer and model, some of those capsules used 40 volt polarization.
 

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