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How To Keep A Condenser Capsule Clean and Dry [message #3225]

Fri, 07 May 2004 17:01

Klaus Heyne
Messages: 2220
Registered: April 2004

Platinum Member

Preventative maintenance of condenser mics is such an important topic and often so easy to do, that I ask you to read the following, and add to it. It may save you money over capsule restoration or replacement!

How to keep a condenser capsule clean and dry

Quote:

Wouldn't a wind-screen do the job?

It would do an excellent job to keep microphone specialists employed with capsule cleaning jobs!

Please use wind socks/screens only when nothing else will do to prevent popping or wind noise from exciting the capsule. Wind socks are made of open-cell plastic foam which starts deteriorating within 1-2 years after manufacture; thereafter its disintegration accelerates. Fine foam dust and flakes will quickly penetrate through the screen and be deposited all over the (electrostatically charged and therefore attractive) capsule area. The final stage of this material is that of a semi-liquefied goo, and then the fun begins...

Try this test with your windscreen: rub your fingers against it over a white piece of paper. If foam dust is deposited on the paper, throw the screen away. It will be harmful to the capsule, and be more costly to use than to replace.
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The best, cheapest (free) and all around easiest way to preventing a condenser capsule from deteriorating is the good old plastic bag from your supermarket's produce or cereal/candy department (you may have to look a little harder for a bag that is made of a bit thicker plastic material, but it will last longer.)

Just put the bag over the mic on the stand, if you cannot tear down the recording set up for positioning reasons. Then, after the session is finished, permanently store the mic in this bag inside its proper case. No need to seal the bag tight. You can let the mic breathe.

If humidity in the room was excessive, you would already have had moisture back- down on the capsule, so no need to worry if the bag fits too tightly. If anything, a bag over a warm tube mic will force redistribution of the higher humidity sitting on the capsule towards the drier amp region of the mic, so the bag will somewhat act as a capsule dehumidifier.

The main idea of the bag over the capsule is that of a physical barrier- to prevent the electrostatically attractive capsule from sucking in particles from as far as six feet away, and letting these contaminants act like salt crystals which catalyze fog formation: If there is any amount of a dirt layer, it becomes that much easier for moisture to form droplets and start a conductive path to short out the two plates of the condenser (diaphragm and backplate.)
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Silica-Gel bags are an excellent way of drying an overly humidified capsule, but only if you tightly restrict the volume of humid air getting to the moisture-hungry silica crystals.

Placing a silica bag next to the mic grill without otherwise restricting its access to air may be well intended, but is useless: Silica is so hygroscopic that any access to unlimited amounts of air will neutralize the silica within minutes.

So here, then, is the proper way to dehumidify a condenser capsule:

First, dry the Silica bag as directed, usually printed on its side. I place it in a conventional oven or toaster oven, set to ca. 350-400° Fahrenheit (175-200° Celsius) for 3-6 hours.

I then immediately remove the bags (I buy more than one, they are cheap) and place them in a sealable canning glass jar, until cooled to room temperature.

I then remove the bag(s), place them against the grill of the mic, and immediately enclose the mic and Silica bag in a plastic bag which I tightly seal. This forces the crystals to suck the limited amount of moist air from the capsule area of the mic head and prevents the crystals to neutralize too soon from too much exposure to ambient air. I save the unused Silica bags in the sealed container until needed.

Quote:

I want to confirm that there is no danger in using plastic bags over my condenser mics.
Wouldn't plastic trap moisture or allow for condensation to occur? Is there any advantage to using plastic versus a cloth bag with a tight weave?

There are a few issues which need to be considered when choosing between cloth or plastic:

Cloth needs to be absolutely lint-free to help in capsule protection, and will of course not prevent excess ambient moisture to enter the capsule area.

You are right: a tightly closed plastic bag will trap any amount of moisture present at the time of wrapping inside the capsule cavity, and may even cause condensation upon temperature change.

So choose your protection according to the task at hand:

If the recording environment is fairly low in ambient humidity (up to 60%) I would tightly wrap the mic in plastic before storage or shipping.

If the mic has been exposed to a lot of moisture while in use, I would either use a lint free cloth bag for storing, or use a plastic bag that is open enough to let the excess moisture inside the capsule cavity equalize with the (lower) ambient humidity in the storage area.

Klaus Heyne
German Masterworks
www.GermanMasterworks.com

Recording Engineering & Production: Making records better, not just louder and cheaper. The brightest minds from the creative and scientific world of audio discuss the elements of audio production that interest you most.

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