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Microphone inside a hermetic capsule...


Advanced Member level 2
Jan 29, 2004
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What material would attenuate/alter the least a dynamic microphone performance if put to work inside a capsule to protect it from corrosive splashes?
A capsule made of flexible film like silicone, cellophane, or polyethylene,... or a rigid like aluminium foil; something else you would dare to use/try/suggest ? :unsure:
Are you looking at one specific fluid or trying to make something

Dynamic elements I've seen are all polymers in the front, only
exposed metal is the magnet butt and the solder tabs generally.
So this might survive caustic and acid splash fine if you just
potted the backside to suit.

A taut light membrane would be best for fidelity, you might find
a resonant peak from it that wants special correction downstream
(kettle drum style).

A condenser mic could be made by putting a plate behind a
membrane as above, biased and fed to a JFET buffer. That is
what a condenser mic is only not with rugged / resistant
materials. You could pick and choose.

A piezo element is yet another unique material system that might
survive certain chemicals. It could also be bonded to any flat wall
and pick up case microphonics pretty well (for better or worse).
Any film/foil thicker than a few micrometer must be expected to affect microphone operation, particularly attenuate high frequency sound. In so far it's a compromise between intended sound quality and protection effect.

PE cling film would be my first option.
Thank you, gentlemen.
Being the desired intended 'capsule' evolved from a loose wrapper; I had done before a simple perceptive-only test, not measuring attenuation or distortion or frequency response yet. 'Capsule' may be interpreted as rigid.

Put my head inside an usual supermarket plastic bag, elastic held tight only around the neck, and could not discern any difference in volume or intelligibility. I do not understand the lack of sounds degradation to my ears. Repeated with a thinner bag of the same, equally acceptable like if a non-existent barrier. So for a wrapper, a loose non-taut polymer film should work. (to be sealed tight at the microphone cable)
Is there any explanation of the minimal or non-degradation of sounds through a plain bag ? 🤔 Have not tried thicker materials.

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