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Re: Physics of moisture-induced mic noise

Subject: Re: Physics of moisture-induced mic noise
From: "Rob Danielson" danielson_audio
Date: Wed Jan 6, 2010 7:15 pm ((PST))
At 1:44 AM +0100 1/7/10, Klas Strandberg wrote:
>At 20:45 2010-01-06, you wrote:
>>Richard Lee wrote that the gap in true condenser
>>mics is sealed. Does this mean that no dirt or
>>moisture can get into the gap? Rob D.
>All omnis are "sealed" between the membrane and electrode, but
>still... I mean, I have seen camera lenses with mould growing between
>two glued lenses.
>Double membrane cardioids are "sealed" too, but - as omnis - must have a
>small air-intake, a air pressure leveler," otherwise the membranes
>will blow up and crack at a high altitude, even in a airplane.
>Cardioids are "fully" open, as the sound must go through the sides of
>the mic, through the electrode and backwards at the membrane, out of
>phase. As I see it, cardioids must be the most exposed for dust and
>other pollution, unless they are double membranes.

I see. I guess another unexpected variable is the
capsule types range a lot. The NT2000's are
double diaphragm multiple-pattern capsules, the
NT1-A's are cardioid, the AT3203's are omni's and
the mkh 40-30's are cardioid/figure 8 RF's.

>I'll have a chat with my friends about your "coping to humidity" topic.
>Are you sure that the base response is the same after the "coping"?

No change in bass response or noise performance that I can detect.

>My first thought was that the membrane slacks cause of humidity and
>gets sucked against the electrode and that something happens then
>that make the mic work, in a limited way, but without clearly audible
>pops and noise.

I'm not hearing any deterioration in frequency
response, transient response or self-noise. I
juxtapose files made with the same mics over the
Message: 2.
Subject: 5 year period quite a bit. I would notice a
change pretty quickly.

>Some studio mic=B4s behave that way if you blow into them. The membrane
>gets stuck to the electrode and you must turn off the phantom power
>for a minute or two, to make it go free again from the electrode and
>get full base response.
>That was one of the reasons why Neumann put a "screw in the middle"
>of the membrane and made others follow. The one inch China mic=B4s I
>have seen has been Neumann copies in that sense, as they are much
>easier to make.
>I'll get back to you when we have discussed the "coping" matter. It
>is interesting.

Thanks! Rob D.



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