My studio is sealed off for the winter. How cold is too cold for microphones? At what point does it become dangerous for a capsule?
Gunnar Hellquist wrote a nice summary of major points to consider when stroring mics in cold climates:
I have a bit of experience of cold climates as I live in Sweden which can at times be a bit on the cold side.
First and most, moisture is your largest enemy. As the temperature goes down, air progressively loses the ability to hold water as a vapor. And what water there is has to condense out somewhere. This condensation can lead to several problems, rust is one of them. It may also directly affect a microphone if it condenses out in the wrong places. As it goes below freezing any water will turn into ice, and as ice has a larger volume than the same amount of water it will expand.
So in order to prepare for low temperatures, keep things as dry as possible and then gradually lower the temperature, while keeping things ventilated.
Water becomes a worse enemy if the temperature goes up and down fast. You can try this easily by putting a glass in the ice box. Wait a few hours and take it out, watching the water condensing on the glass. This will happen to your equipment when it goes from cold to hot air.
In sum, a dry room, which you keep at least a few degrees above freezing would be a good thing for mics. A closed locker with ventilation may help. It might be a good thing to invest in air drying if there is a large investment in equipment. Air dryers come in several variations. Some of them do work even in sub-freezing temperatures. You may look at the following link for desiccant dehumidifiers. That kind of equipment is used among other things for long time storage of military equipment in non-heated spaces (going well below freezing).http://www.munters.com/
A crucial temperature limit to look out for is freezing (0 C or 32F). At this temperature, or perhaps a few degrees above or below, water freezes. Dry equipment will not be effected, but condensed moisture may create problems. Repeatedly cycling temperatures above and below freezing is generally not a good thing as the warm air carries moisture into the equipment where it later condenses. Below zero storage should be less of a problem.
Here in Sweden, I store my mics in boxes, together with some moisture catching silica bags (see Klaus Heyne's Stickies article: "How to Keep a Condenser Capsule clean and dry")
The boxes go into a larger wooden box with some foam (not really for isolation, mostly for mechanical protection). This box is stored in a storage room which does not change temperature too often. It may stay in the car booth even on a really cold day (down to about -30C or -22F), but I take great care to let things warm up very very gradually, before opening the box- to avoid getting condensation on cold equipment (any person wearing glasses knows what I am talking about). Putting the really well dried equipment in sealed plastic bags before going out in the cold helps when later "defrosting" things.