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Author Topic: Dirty Capsules: Do-It-Yourself Cleaning?  (Read 9306 times)

Offline klaus

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Dirty Capsules: Do-It-Yourself Cleaning?
« on: May 05, 2015, 03:59:26 pm »
When enough dust, dried spit and other air-born contaminants have settled permanently on a 6µ or thinner diaphragm, there comes a point when the weight of that debris will affect the transient response and high frequencies: too much weight on the diaphragm slows it down.

Another issue caused by capsule contamination is break-down of capacitance. 
A condenser microphone capsule consists of 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 (usually around 5-7µ) but incredibly high isolation resistance: ten-thousand million (10gig) ohms  or more. Close distance and high isolation between the two capacitor plates makes it imperative to keep both components meticulously clean.

If the isolation resistance is reduced through dirt accumulation caused by spit, aided by the electrostatic attraction of airborne particles to the charged capsule, the capacitance formed by the two capacitor plates (condenser is another word for capacitance) is suddenly reduced or shorted completely.

Capacitance collapse will render the capsule inoperative, i.e. sound will fade in and out, or lots of discharge sounds, from thunder to whistling noises ensue. The process of deterioration is accelerated when moisture or humidity is present: moisture helps to conduct electricity between individual dirt particles, and thus forms a conductive path. And as soon as conductivity between diaphragm and backplate is created, the capacitance between the plates discharges, and renders the capsule inoperative. Some capsule designs are structurally 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, all dirt and moisture must be removed, to regain the super-high impedance between the relevant capsule parts.

I have always been reluctant to self-promote on my forum, and continue to try to resist it. But I am passionate about correct capsule cleaning, and its many amateurish, destructive attempts continue to irritate me. The frequent mentioning of distilled water as cleaning agent is fraught with peril: contaminants floated through water can easily penetrate the minute gap between the plates and permanently settle there. Mechanical contact with the gold sputtering of the diaphragm by means of brushing a liquid over it has further the disadvantage of scraping dirt particles into the angstrom-thin layer of gold.

Capsule cleaning is an art, based on science, and I continue to warn mic owners to not try to use mechanical means in attempting to clean a diaphragm, backplate, and its associated high-impedance components. There are methods to restore a capsule back to factory specifications that do not involved mechanical rubbing. I have developed such method, and others may have as well. It is vitally important that any microphone owner who suspects capsule contamination interviews service providers as to the method they use to remove the contaminants. In case of doubt, I recommend to buy a new or used, but clean capsule, rather than turn the defective capsule over to an amateurish cleaning attempt.

My aversion to "reskinning" (re-diaphragming) capsules, including heavily contaminated ones, will be subject of another sticky. But I have not found many that could not be restored to factory specification through proper cleaning.
« Last Edit: July 12, 2017, 09:56:56 am by klaus »
Klaus Heyne
German Masterworks®