"Frying hizz" from condenser microphones

[johnheath]

Hi all...

Me and a couple of friends of mine sat down to do some "living room recordings" and we used all the mics we had and after a while we could hear some strange sounds and started to track down the source.

The sound is a bit hard to describe but it sounds like something being fried in a pan... "fffrrsss - ffrr- ssssrf" and so on (I hope the description make some sense)

The preamps and compressors and EQ's are all home-brew DIY stuff so an obvious reaction was that i could be something wrong with those but after some highly irritating coupling back and forth showed that the noise came from some of the condenser mics (As we could understand).

The mics I am referring to is a "Rode NT2-A" when the "directional switch" is set to Figure 8... no noise otherwise and the other mics are the Line CM3.

It might be said that other mics like Neumann KM184 coupled to the same type of preamps and compressors worked just fine for hours without any noise what so ever.


So... I would really like some hints on what this could be to be able to solve the mystery.

Thanks


/John

 

[RuudNL]

High humidity and/or capsule pollution.

 

[johnheath]

Thank you sir

Actually we began talking about humidity because it was very warm and damp in the room after an hour or so... but then... why didn't this happen to the other mics?

And is there something I can do to prevent it from happening... yes, without being in a bigger room with excellent air conditioning?

Best regards

/John

 

[RuudNL]

It depends on the type of capsule.
Capsules with a center screw are usually more sensitive to high humidity than edge terminated capsules.
In an environment with high humidity, moisture on the capsule creates some conductivity between the gold covered part of the membrane and the tensioning ring. This leak current (we are talking about impedances of 1 G.ohm or so!) is the cause for the
"fffrrsss - ffrr- ssssrf". If the surface of the capsule is contaminated, this will occur earlier than with a 'clean' membrane. (But of course to a certain extend...) If the capsule is clean, the problem will disappear when the microphone is 'dry' again. (In an environment with low relative humidity.)

 

[johnheath]

Thank you sir

In fact the noise is not present when connecting those mics the day after so it could very possibly be the problem... with humidity.

I guess I will have to watch out for long recording sessions in small rooms with poor ventilation?  :

Best regards

/John