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Gear / Technical Help => Microphones & Setup => Topic started by: Vurki on May 29, 2010, 10:40:21 AM
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It's obvious that humidity effects on condenser mics - everyone says that. But what there really happens? I have been searching information from this site and with google but I can't get answers to two main questions: 1) is the effect permanent or temporary, I mean, does the humidity only cause some malfunction to the recording or does it cause some permanent damage to the microphone and 2) how much does the humidity effect? Is it dangerous in general to record outdoors with large diaphgram mic after a rainy day, if the current day is sunny? I'd like to know how these things are, because otherwise I won't dare to make field recordings at all!
Thank you.
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I can't really answer your first question scientifically but I can tell you that in anecdotal experience the effects are temporary. If you dry out your mics (under a light bulb or some other gently warm and dry place for a day or two) there are generally no after effects.
The only mics I ever heard from someone I know having humidity problems were Jim Williams modified AKG 460s. I had a pair and read up on it but never had that problem myself. People claimed that it came from "cracking the case" do do the modifications but I can't really tell you why.
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IIRC the effect is a crackling sound in the audio and it is not permanent if the mics are dried out with an anti-dessicant or put in a dry room. Check with DSatz for the real story.
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Thanks. I searched for DSatz and found a lot of information. It seems like it really isn't permanent and that it's not that exact at all, but I'll still continue searcing to be sure. Of course, you can share your knowledge here too :)
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It's obvious that humidity effects on condenser mics - everyone says that. But what there really happens? I have been searching information from this site and with google but I can't get answers to two main questions: 1) is the effect permanent or temporary, I mean, does the humidity only cause some malfunction to the recording or does it cause some permanent damage to the microphone and 2) how much does the humidity effect? Is it dangerous in general to record outdoors with large diaphragm mic after a rainy day, if the current day is sunny? I'd like to know how these things are, because otherwise I won't dare to make field recordings at all!
Thank you.
OK - here is the blurb I normally give when asked this question:
Basically, AF capacitor microphones use the capsule as a capacitor to store charge. With one fixed plate and the other free to vibrate in sympathy with the sound, the capacitance varies, and the charge moves in or out of the capsule accordingly. This is measured by the head pre-amplifier and an audio signal results. All well and good, but the capsule is inherently in a high impedance circuit (over 1GigaW) – it has to sit there with stored charge until the diaphragm moves and any changes in the charge are perceived as audio. In a humid atmosphere the stored charge finds it easier to escape on water molecules in the air rather than through the input of the pre-amplifier, hence noisy and reduced output, and misery all round. The high biasing voltage also attracts dust particles to the diaphragm, reducing its efficiency and linearity.
The RF system (as used in Sennheiser MKH microphones) uses the capsule (a low impedance capsule) in a completely different way: as a tuning capacitor for an RF oscillator – which inherently employs it in a low impedance circuit where a high frequency signal is being passed through the capacitor all the time. Changes in capacitance (caused by sound moving the diaphragm) alter the resonant frequency of the circuit (circa 8MHz) and so its frequency becomes proportional to the audio signal. A simple RF demodulator restores the output to a conventional audio signal. More complex and sophisticated (but still very rugged), this system is highly immune to the effects of humidity and is thus the preferred design to be used out of doors (or when moving from outside to inside on a cold day!).
The effects show up as noise or crackles - but it does not permanently damage the mic. Left in an airing cupboard (for example) to dry out and it will be back to normal again.
I hope this helps.
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Thank you John Willet. A late reply but who cares, I don't need any further information anymore.
Ty for all of you :)
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Thank you John Willet. A late reply but who cares, I don't need any further information anymore.
Ty for all of you :)
Your reply actually sounds kind of rude. You might want to rethink it. "A late reply but who cares, I don't need further information anymore" Sounds very rude. You might want to say "Thank you John Willett, I appreciate it."
Chris
Actually, although I read it as you did from the first reading. Looking a second time I then read it as *his* reply was late - my original reply was the day after he posted.
I also understood it to read that my reply was comprehensive enough so that he didn't need any more answers.
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I'm pretty sure I had an issue with this during Max Creek's sets at Strangecreek last weekend. I ran every other set that weekend with no issues but during the Creek set it was super moist and muggy out. The music is there but there are these spikes you can see in the wave form where the music dips out and there is a spike in levels but not music. Ran more music a day or two after that set with no issues again. It was the only thing I could think of to cause it.
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Some operating specifications for sound equipment distinguish between "condensing" and "non-condensing" humidity. As far as I'm aware or have ever experienced, any well-made condenser microphone should have no problem as long as there's no condensation (actual water droplets being formed) within the capsule.
I've recorded outdoors a fair number of times, including a lengthy series of sound effects recordings at Walden Pond early on some foggy mornings, with no problems that I could hear, using Schoeps microphones. And if operation should be disrupted due to condensation, that won't harm any well-designed microphone--just bring it indoors, leave it powered up for ten or twenty minutes, and it should be good to go again.
But I have to confirm what John Willett says about the greater reliability of RF condenser microphones in extreme cases such as tropical rainforests; I'd be lying if I denied that.
--best regards
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I've recorded outdoors a fair number of times, including a lengthy series of sound effects recordings at Walden Pond early on some foggy mornings, with no problems that I could hear, using Schoeps microphones. And if operation should be disrupted due to condensation, that won't harm any well-designed microphone--just bring it indoors, leave it powered up for ten or twenty minutes, and it should be good to go again.
Yes, a good clean Schoeps can be good outdoors.
But remember that an AF mic does tend to attract dust and particles by electrostatic action, and if these stick to and build up on the diaphragm they can absorb moisture and then you have the problem.
I was talking with Joerg Wuttke of Schoeps a few years ago at the weekend conference of the Institute of Broadcast Sound in the UK and he advised returning them to Schoeps for cleaning occasionally to keep them working at their best - this was him talking to film and TV sound recordists who use mics outside all the time.
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I had significant problems with humidity effects in a pair of LD mics recording in summer festival environments. The cracking was enough that it was obtrusive to the recording. Although I'm not 100% positive that it was caused by humidity effects, it's the most logical explanation since the problem didn't seem to replicate during indoor shows.
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I had an LSD2 with a bad capsule... it would crackle and drop out with a much higher amplitude than the music I was recording. I sent it to be repaired, they couldn't repeat it. They are in the California desert, and I'm in a reasonably muggy environment. Eventually they did see it when they "gave it the mist test" or something like that, and replaced both capsules with new ones and it was great after that.
The way the tech explained it to me is this.... the capsule has plates a tiny distance apart and they have a voltage across them. Imagine there is a little piece of dust in there... it's supposed to be perfectly clean, but imagine it's not... if the piece of dust is bone dry it doesn't conduct any electricity, but if the piece of dust gets damp, it starts to arc out in there. Hence the way you will frequently see a giant sudden POP and then the signal decays back into normal shape as the charge builds until the next pop. Makes sense to me.
I live in Maine where it gets cold in the winter... I think the big challenge isn't so much the rainy day festivals (which everyone thinks about), it's leaving the mics in the cold car, then pulling them out in the warm club where the condensation builds on them like a cold can of beer on a summer day.
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... I think the big challenge isn't so much the rainy day festivals (which everyone thinks about), it's leaving the mics in the cold car, then pulling them out in the warm club where the condensation builds on them like a cold can of beer on a summer day.
Exactly what I said at the end of my earlier post. ;D
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"cold can of beer"... mmm...
On a slightly more serious note, great explanation, Joe and John.