Sennheiser MD21 / 421 / 441 / 409 etc. family // capsule tuning tricks

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raketenmann

Active member
Joined
Oct 20, 2021
Messages
39
Location
Switzerland
Dear DIY-community

In the last couple of years I learned a lot from repairing microphones. There was a lot of try and error - but over the years I gathered a lot of experience and also know how of the design of dynamic microphones. But still I am not an expert.

I experienced a lot of problems related to the physical condition of the diaphragm and resulting in coil rub or altered midrange etc.. I also found out that AKG mics (e.g. D12, D19, D1000, D2000 etc) tend to have way more problems with deformed diaphragms than Sennheiser mics.

In most MD-family mics I find the diaphragms in very good condition, sometimes dirty, sometimes cleaned, but almost never there seems to be deformation or physical damage. Still, sometimes I run into capsules that seem to have a tiny bit more high end than others, just in the range above 10k, shortly before the response of most dynamis end. I did a lot of experiments with different foam and windshield, especially on MD409 capsule with no significant differences. From all I know, the amount of High end in a dynamic capsule is altered by the following factors:

- mass of the diaphragm (altered by dirt & magnetic dust on vintage mics)
- resonator plate under the diaphragm (altered with sag on old mics)
- resonator plate on top of the diaphragm (altered with sag of the diaphragm)

These informations are based on this article here:

https://www.audiotechnology.com/tutorials/dynamic-microphones
So, based on these information and my experience with lacking response in the range above 10kHz, I assume that there could be some improvements by repositioning the resonator disc. So I wonder: What would be the goal? Does the gap between the dome of the diaphragm and the resonator disc need to be smaller or bigger? If the dip in the high end has tod o with some diaphragm sag, this would result in a bigger gap between the dome and the resonator disc. So therefore probably the disc would need to sit a little closer to the diaphragm.

What are your thoughts about these matters?
 
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