> My attempt to save them is to try storing them with desiccant --
> perhaps over the years moisture has diffused into the capsules, and
> perhaps a good long drying-out will restore them.
Dan,
If the moisture has penetrated over years, it may take time to get it
out. If the moisture is within the capsule it may have to evaporate
out through the diaphragm. If you have a reasonable quantity of silica
gel which you can keep activated, store the mics in a sealed box in a
warm place as standard.
Using rice is not as good as silica gel and it also has to be dried
out to be efffective. My regular alternative tip is to use wool, such
as an orphaned sock, ironed bone dry with a hot iron. Silica gel is
the dryest at about 15%, but it has only a small capacity for
absorbing moisture (see link below).
> I've tested them by putting them into a freezer and listening for
> pops. In my recent test run six of nine capsules started popping
> within 20-30 minutes. Admittedly this test may be extreme, but I'm
> trying to accelerate the effect of internal condensation.
And Phil said someone heated theirs. Not a good idea as it is likely
to spread the moisture around inside the mic let alone damage
components. What you don't want is for the electret element to get
damp and discharge.
With mics that undo, a smear of silicone grease over the capsule
connection insulators helps stop tracking especially with high voltage
non-electret capsules, but I think the cure long term drying out.
> I'm experimenting with measuring the humidity in the bags by sealing
> in my Kestrel 3000 weather station and taking a reading a couple of
> hours later. The minimum humidity I observe is around 15%. I was
> expecting it to go lower.
That's about right for silica gel at 10% absorbance (ie fresh). It's
time that's needed. See chart 2 on:
http://www.sorbentsystems.com/desiccants_charts.html
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
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