Sennheiser MKH capsule question

zebra50 · Nov 5, 2022

Hi there

Does anyone know if the old Sennheiser MKH 405 series capsules will tolerate normal DC polarisation or will they be pulled into the backplate? I know these MKH mics are RF types.

I have a couple of salvaged capsules to play with but am getting some odd results when used in 'normal' mic circuits.

Thanks for your thoughts.

Stewart

rogs · Nov 5, 2022

I have always assumed that all the Sennheiser MKH RF mics probably use low tension capsules?...
The later (post 1985) MKH mics use symmetrical low tension capsules, but the earlier models (404,405, 415 etc ) used more conventional capsules. As they were never likely to encounter high voltage DC polarisation, I would guess they did not use high tension membranes?
Certainly the description of the earlier models here: Sennheiser Electronics Corporation MKH 415 T | RecordingHacks.com specifically mention low tension capsules.
If the capacitive value of the 405 capsules are within the 65pF - 85pF range you might consider trying them out with the RF circuitry I used for my RF project? (www.amx.jp137.com ). As you're in the UK the IF coils should be easy to obtain .
Just a thought...

zebra50 · Nov 6, 2022

Hi Rogs

Thanks for sharing your thoughts. Your suggestion of low tension matches my experience here with the capsule under DC conditions. It seems to oscillate as it sticks to the back plate and then releases again. I will try to lower the voltage and see what happens.

Your RF project looks excellent - very well done.

Cheers
Stewart

jarvis · Nov 6, 2022

Hey,

as Rogs said, if they're anything like the later models (MKH 40 etc.), they'll have a pretty low tension as well as a pretty small spacing between the membrane and backplate(s), which is an unfortunate combination for "usual" polarization voltages.

Another problem with using them in a conventional circuit (i.e. Schoeps) is that the membrane is not damped very much and, in conjunction with the low tension, that leads to a pretty peaky response in the midband, which they make up for with an equalization stage in the preamp. Thus at least the newer model's capsules will not sound very good with a flat preamp.

I'm not sure about the older models but some of these aspects might be true for those capsules as well, so using them in an RF-circuit might be your best bet.

Best
Jannis