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Re: Physics of moisture-induced mic noise (was MS-stereo and figure-

Subject: Re: Physics of moisture-induced mic noise (was MS-stereo and figure-
From: "Rob Danielson" danielson_audio
Date: Mon Jan 4, 2010 8:29 am ((PST))
At 10:06 PM -0800 1/3/10, Gregory O'Drobinak wrote:
>There are way too many variables to pin down here without lots of
>time and a full lab to work in.

Hi Greg--
Since the moisture problems go away or greatly lessen when the mics
are powered-up and outside, this is a significant _constant_ and one
we can apply and base improvements on. Planning to set-up and power
the mics well in advance is doable if the recording opportunity is

>With regards to some previous emails on this subject:: replacing a
>mic capsule with a capacitor may be very difficult to do quickly
>unless you have a de-mountable capsule such as the Oktavas. Even
>then, how do you get a good stable contact to the center pin and
>ground without making a special machined head to take the place of
>the capsule. And be sure to have all of this stuff ready exactly
>when the "noise event" starts, then keep the environmental variables
>that provoked the event stable. Maybe the noise is caused by a bad
>("cold") solder joint somewhere within the preamp that acts up under
>certain conditions. How do you test this? That effect can be very
>sporadic. BTW, I once had some noise events caused by a bad battery
>contact in the phantom power supply.
>My advice is for those of us who have had these problems is to put
>together a database of the model of mics, noise events, conditions,
>time, age of mic, etc., to see if there is any type of correlation
>that can be gleaned form this data. Perhaps a pattern will never be
>found. But at least we can perhaps get some idea of what mics have
>what problem under what conditions.

You and Dan are right that it will help a lot to become more
methodical in our efforts to track the variables. A few years ago, it
was thought that the only work-around was to buy RF mics. Now we know
that the problems and solutions do have patterns and that much less
expensive and equally reliable options exist.

I recently created a folder on my computer where I place mic noise
recordings and include the mic serial number, time and weather info.
I wish I had started this obvious practice two years ago! Right, its
best not to keep the records in our heads or clog-up the list with
reports of single events.

As for associated weather conditions, in the US, NWS has charts and
spread sheets which one can download and save with the sound
recording to get the conditions hours before the event.  Choose the nearest citizen or gov weather
station to you.  (This link seems to have a quick redirect today. I
hope they are not in the process of restricting access. Might be a
good idea to get some local links in your browser bookmarks)

>Mics that perform well and that don't make it to the "event list"
>would probably be good candidates for field work.

I think the list is a lot longer than we thought in prior years if
precautions are taken. :-) It might also help the cause to think less
about "bad" and "good" mic models because we suspect that this is an
incomplete and misleading way to look for better solutions. Rob D.

>Peace & Happy New Year!
>From: Rob Danielson <<>>
>Cc: Richard Lee <<>>
>Sent: Sun, January 3, 2010 9:23:01 PM
>Subject: RE: [Nature Recordists] Physics of moisture-induced mic
>noise (was MS-stereo and figure-8 mics)
>At 11:06 AM +0000 1/4/10, Richard Lee wrote the below to me (Rob D.)
>He attempted to post it to the natrec list.
>Rob D. asked initially:
>>>AT-3203.." fixed-charge back plate permanently polarized condenser."
>>>is this an
>>>electret mic capsule, not a "true" condenser?
>Richard replied:
>>This is a back electret. Some of the best mikes in the world including th=
>>Shure SM81 & DPAs are back electrets.
>Richard wrote (trimmed):
>>...The most stringent condition most studio mikes face is being
>>taken from the
>>boot of a cold car into a warm & humid room. Moisture condensing on the m=
>>backplate & other bits forms a leakage path.
>Yes, moving from cold to hot and vice versa greatly increases the
>chances but the examples of several types of mics with almost perfect
>immunity to all types of moisture induced noise have stayed outdoors
>2-3 months. A few have taken a couple of months longer to completely
>Richard wrote (trimmed):
>>...Cleanliness is a major factor. If you bring a scrupulously clean but c=
>>backplate into a warm humid environment, a very fine mist of
>>condensation will
>>form & go away quickly as the capsule warms. If there is the slightest
>>contamination, the condensation will bead & form much bigger drops.
>>These will
>>carry contaminants into the gap & other places they shouldn't go
>I and the other recordists used no special covering/protection from
>airborne materials other than typical wind screens. It has been dry
>and dusty at times too. After being out for months, the capsules
>appear quite a bit dirtier. I don't know what to say except that more
>dirt doesn't seem to be the cause of more noise, because the noise
>lessens as the dirt accumulates.
>Rob wrote initially:
>>>...I've observed 6 or more condenser mics make transitions from
>>>fizzing to sputtering to regular popping to very rare popping over
>>>the course of 2-3 months of continuous, outdoor use.
>>I don't know what this is. Never (have) come across it.
>We discussed it on the miclist a little over a year ago.
>>What mikes have done this for you? Electrets? RF mikes? I still
>>think its an electrical phenomena.
>Rob :
>NT2000's, NT1-A's AT3203's and MKH's.
>Rob wrote initially:
>>>Maybe one could "see" the discharges with the right tools?
>>At the voltages involved, there really isn't a "discharge".
>Rob wrote initially:
>>>.. outdoors to condition them with the imperfections of air ..
>>It may be the mike has simply achieved thermal equilibrium with its
>>surroundings. It's sudden changes in temperature/ humidity which leads to
>Thanks for the input. Maybe there's a form of "equilibrium" that
>takes months to fully achieve?" Rob D.


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