[Top] [All Lists]

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: Sun Jan 3, 2010 6:45 pm ((PST))
At 4:16 PM -0800 1/3/10, Dan Dugan wrote:
>  > (1) Audio Technica describes the AT-3032's element as,
>"fixed-charge back plate
>>  permanently polarized condenser." I asked this
>>  before and I don't recall an answer, is this an
>>  electret mic capsule, not a "true" condenser? I
>>  think the Sennhesier ME series mics might fall
>>  into this category too.
>I think when people say "true condensor" they mean "high-voltage
>externally-polarized condensor." Such mics can be quieter and have
>higher sensitivity. Typically a manufacturer's top line will be
>high-voltage condensors, and their mid- and low-priced lines
>electrets. Yes, the ME-series is electret.
>You know how sometimes a piece of plastic can get charged, you keep
>wiping dust off it and it keeps attracting it back? That's the
>principle of the electret.

Thanks for helping me clear that up.

But, if we assume that small electrets and then larger electrets are
fundamentally more immune because of their design, its inconsistent
with the fact that much larger, non-electrets tend to become just as
immune, if not more.  Rich Peet has four 3032's that are outside most
of the time and none of them exhibit noise issues. I know its hard
for people to get a handle on, but it seems that outside exposure is
a more common trait of moisture immunity than capsule design.

>>  If so, its
>>  well-documented that recordists can get moisture
>>  related issues with all of these mics--
>>  especially in the first several hours of
>>  operation under provoking humid conditions.
>In my experience electrets are a lot less sensitive to humidity, but
>one or two of my 3032s have been screwing up while left out
>overnight--last expedition I had to get out of the sack just before
>dawn chorus to swap one that was motorboating. Brrr. But three of
>the four were fine!
>>  Its rare for recordists to
>>  leave mics on and outdoors continuously, but it
>>  occurs to me that one could actually study the
>>  duration-induced phenomenon, maybe with a
>>  microscope of some capsules, to find out what is
>>  producing the physical change and build this
>>  "change" into the mic at the outset. Maybe one
>>  could "see" the discharges with the right tools?
>>  I have no idea about the science that would be
>>  involved but I thought it might be worth
>>  mentioning again.
>My easy test is to pop them into the refrigerator (not the freezer)
>at around 40 degrees F and listen. It can be only a few minutes
>before a susceptible mic can start making noises. BTW when you have
>sets of identical things it's important to label them all so the
>individuals have identity.

Good trick and much easier than waiting on the the weather. How about
cranking the frig temp down for an hour or too before things start

Swapping capsules and electronics is another way to start isolating
the factors. There is quite a bit of erratic behavior to contend
with. One capsule can show total immunity for months and then act-up
two times in a row under "ripe" conditions and then stop again for
many months. But still, there seems to be huge change that happens
over the first 2-3 months compared to the erratic behavior one
typically gets with mics that have not yet been subjected to long

>It seems obvious but I didn't know till recently that the 3032
>capsules unscrew. I think when I tried to unscrew my first one and
>it didn't budge I assumed that they didn't. Now I have to label both
>the capsules and the bodies.

That's very interesting. Can you post a photo of the capsule and how
it got liberated? I think you may be the first consumer to achieve
this and witness the insides. I recall that Mike Feldman and some
other folks were stymied. Rob D.

>-Dan Dugan


<Prev in Thread] Current Thread [Next in Thread>

The University of NSW School of Computer and Engineering takes no responsibility for the contents of this archive. It is purely a compilation of material sent by many people to the naturerecordists mailing list. It has not been checked for accuracy nor its content verified in any way. If you wish to get material removed from the archive or have other queries about the archive e-mail Andrew Taylor at this address: andrewt@cse.unsw.EDU.AU