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Capacitor microphones and humidity problems

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Capacitor microphones and humidity problems

Postby ef37a » Thu Feb 14, 2019 5:34 pm

Do any of you find it a problem?

I have but 3 capacitor mics, two AKG P150s and a Sontronics STC-2 and have used them little in the last few years but they never give me any trouble even though stored in an unheated room.

However, on another forum the matter of damp is seized upon, alligator like, whenever anyone asks about an issue with a capacitor mic.
Are they really this sensitive to humidity?

Then the "CIS" idea of a bag of rice is always trotted out but I understand it doesn't work?

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Re: Capacitor microphones and humidity problems

Postby Wonks » Thu Feb 14, 2019 5:44 pm

It's normally when a mic has been somewhere cold for a while, then brought in somewhere warm but with more moisture in the air, and the mic is cold enough for the air around the mic to hit dew point and the water vapour will then condense out on the capsule and electronics.

Dirt in the air and on the mic surfaces will make the moisture conductive, so the high impedance resistor to ground's practical resistance drops, and the moisture can bridge, or partially bridge, the front and rear of the mic capsule, lowering the capacitance and messing with the signals.

Kept in the same location, certainly above 14°C you should be fine all the time, and if down to 10°C, then you should be OK unless there is very high relative humidity in the room.

Don't forget that moisture from your breath can add to the relative humidity load, and can sometimes just tip a mic over the edge when in use.
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Re: Capacitor microphones and humidity problems

Postby Hugh Robjohns » Thu Feb 14, 2019 6:20 pm

ef37a wrote:Do any of you find it a problem?

Yes, it can be a real problem... but a great deal depends on the working conditions, the construction of the mic, and how it has been stored and used previously...

Wonks has already explained the mechanisms involved, but it is really only the DC-biased (externally polarised) 'true' capacitor mics that really suffer. RF-capacitor mics (like the Sennheiser MKH range) and back-electret mics are largely immune, the former because the capsule operates in a low-impedance environment, and the latter because the electrostatic polarising charge is generated internally.

If a mic is brought in to a warm, humid environment from a colder one, condensation can form and, since water is conductive, the impedance around the capsule can be lowered dramatically which will compromise or even curtail the mic's operation. However, once the mic has reached normal room temperature any condensation should have evaporated and normal service should be resumed.

When problems persist it's usually because the capsule and/or diaphragm, has become contaminated with dust, smoke particles, or debris splattered on it from an ultra-close vocalist's mouth after consuming half an Indian take-away... :o This last mode is the predominant one, sadly, and another reason why mics should be protected behind pop-screens! Needless to say, the contaminants tend to absorb and trap water, resulting in a semi-permanent residue across the capsule which effectively breaks down the isolation, lowers the impedance, and prevents the mic capsule from working as intended... with frying noises or worse as the inevitable result.

Careful professional capsule cleaning can often restore full service, but it is tricky and it's easy to damage the diaphragm further.

Then the "CIS" idea of a bag of rice is always trotted out but I understand it doesn't work?

Dry rice will certainly absorb atmospheric moisture, but it's not as efficient as the familiar silica gel pouches. And in any case, it's not really getting to the heart o the matter when it comes to noisy capacitor mics. If a day spent in a warm airing cupboard doesn't cure the problem you're almost certainly looking at sending the mic off to be fixed or, with more cost-conscious mics... a new mic!

H
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Re: Capacitor microphones and humidity problems

Postby Wonks » Thu Feb 14, 2019 6:39 pm

Hugh Robjohns wrote:If a mic is brought in to a warm, humid environment from a colder one, condensation can form

It doesn't even need to be that humid for a cold mic to have problems. The dew point temperature for air at 23°C and 50%rH is 12°C. That's a pretty normal indoor temperature and %rH in the UK. So the mic just needs to have been waiting in an unheated warehouse and then an unheated delivery van overnight and you are very likely to get condensation the moment the package is opened.
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Re: Capacitor microphones and humidity problems

Postby Mike Stranks » Thu Feb 14, 2019 7:30 pm

I posted recently about a mic that was sent to me through the post exhibiting all the symptoms of capsule condensation. I have no reason to doubt the sender when he said that all was well when it left him.

A few years ago I sold an expensive mic that I'd owned from new and stored carefully that was working perfectly. Buyer reported it as faulty and sent it back. It was indeed hissing and spitting like a snake. Sent it to a forumite who's a whizz with mics who left it for a few days and then connected it to hear the problem for himself. Problem gone!

I keep all my mics in a purpose-built case with several large bags of silica-gel. The only mic that's always 'out' is protected with a thick foam windshield when not in use to keep any dust away from the capsule.

Capacitor mics are sensitive instruments; because of their ubiquity it's easy to forget that.
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Re: Capacitor microphones and humidity problems

Postby ConcertinaChap » Thu Feb 14, 2019 11:05 pm

A surprising number of things you buy arrive with small bags of silica gel. I always save these and put them in my mic cases. I've never had a problem with a mic in my possession. I did once have a problem with a brand new KM184 when it arrived hissing and spitting away in fine fashion, but a day or so in the airing cupboard cured that.

So in the main I don't think it's a big issue, I know how to avoid it and I know what to do if it arises. If, like Mike's mic, the problem occurs and is not amenable to the airing cupboard treatment then the cause is something else.

Mike Stranks wrote:The only mic that's always 'out' is protected with a thick foam windshield when not in use to keep any dust away from the capsule.

A cheap and easy alternative is a plastic sandwich bag.

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Re: Capacitor microphones and humidity problems

Postby Wonks » Thu Feb 14, 2019 11:24 pm

Providing you first take the sandwich out.
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Re: Capacitor microphones and humidity problems

Postby Sam Spoons » Thu Feb 14, 2019 11:42 pm

:D :D :D

My refurbed studio is proving slightly dry for my guitars (35-40% which is, obviously, brilliant for the electronics,). I cover any capacitor mics left out with a microfibre cloth as humidity is, clearly, not going to be a problem, and they don't usually go out. The mics that do go out on live gigs are in a cheap mic case which is rarely, if ever, opened before they have had time to warm up.

WRT to the guitars, I my have to get a humidifier (which is a real surprise after 15 years of running a de-humindifier 24/7 :headbang:
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Re: Capacitor microphones and humidity problems

Postby ConcertinaChap » Fri Feb 15, 2019 8:39 am

Wonks wrote:Providing you first take the sandwich out.

Ah, thanks. I knew there was something I'd missed. Explains why people kept hamming it up in front of the mics and the cheesy character of the resulting recordings even after I'd egged them on a bit.

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Re: Capacitor microphones and humidity problems

Postby Mike Stranks » Fri Feb 15, 2019 10:24 am

ConcertinaChap wrote:
Wonks wrote:Providing you first take the sandwich out.

Ah, thanks. I knew there was something I'd missed. Explains why people kept hamming it up in front of the mics and the cheesy character of the resulting recordings even after I'd egged them on a bit.

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Re: Capacitor microphones and humidity problems

Postby Wonks » Fri Feb 15, 2019 10:26 am

Crumbs!
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Re: Capacitor microphones and humidity problems

Postby Sam Spoons » Fri Feb 15, 2019 3:20 pm

Did these sessions make you any bread man?
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