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Author Topic: Dirty Capsules: Do-It-Yourself Cleaning?  (Read 20694 times)

klaus

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Dirty Capsules: Do-It-Yourself Cleaning?
« on: May 05, 2015, 03:59:26 PM »

When enough dust, spit and other airborne contaminants have settled permanently on a 6µ or thinner diaphragm, the debris will affect transient response, high frequencies and ultimately the capsule's functionality.

The biggest problem caused by capsule contamination is break-down of capacitance. 
The capsule of a condenser microphone has two functional parts: a diaphragm (or two, in case of multi-pattern mics) and a backplate (or two), against which the diaphragm is mounted at very close proximity, but with an incredibly high isolation resistance: ten-thousand million (10gig) ohms or more.
Such close distance and high isolation resistance requires meticulously clean surfaces.

Once the isolation resistance is reduced, through accumulation of dirt, aided by the electrostatic attraction and settlement of airborne particles on the charged capsule, the capacitance formed by the two capacitor plates (condenser is another word for capacitance) becomes unstable, and the plates eventually short out.

At that point you will hear audio fading in and out, often accompanied by discharge sounds-from whistling noises to loud thunder.

The process of deterioration is accelerated when moisture or humidity is present (for example from a singer's breath). Because moisture forms an electrically conductive path between contaminated diaphragm and backplate, the capacitance between the plates discharges, and renders the capsule inoperative.
Some capsule designs are more resistant than others to that phenomenon, but ultimately, all conventional condenser mic capsules are prone to be affected by dirt accumulation.

To restore the capsule to its original uncontaminated state and super-high impedance, all dirt and moisture must be removed.

Correct Capsule cleaning is an art, based on science. The many amateurish, destructive instructions by self-help advocates and DIY'ers continue to irritate me.

Two examples: using distilled water to clean surfaces is frequently mentioned, but is fraught with peril. Contaminants dislodged and floated through water can easily penetrate the minute gap between the plates and permanently settle there.

Another peril: mechanically brushing a liquid over the mere angstrom-thin layer of gold deposited on the diaphragm often scrapes dirt particles into the gold, removing some of its conductivity and affecting capacitance.

I continue to warn mic owners to not try using primitive means in attempt to clean diaphragms, backplate, and associated high-impedance components. There are methods to restore most capsules back to factory specifications that involve little or no mechanical contact with the diaphragm surface. I have developed such methods, and others may have as well.

It is vitally important that any microphone owner who suspects capsule contamination interviews service providers about the methods used to remove the contaminants. In case of doubt, I recommend to buy a new or used (but clean) capsule, rather than lose the defective capsule to an amateurish cleaning attempt.

Very few capsules, I found, are beyond restoring to factory specification through proper cleaning. My aversion to "reskinning" (re-diaphragming) capsules, especially those heavily contaminated and seemingly beyond hope, is subject of another post.
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com
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