For a couple decades I've made a lot of use of a modified Crown SASS-P stereo mic that incorporates electret condenser capsules in a PZM/quasi-ORTF configuration. It is not the lowest noise option I have but has a unique and useful sound and pick up pattern that works great for drums, piano, acoustic guitar, choir, small classical, jazz, or folk ensemble, or anywhere where a natural stereo image is desired.

I'm mostly very happy with it, but I understand that electret condensers slowly loose their "permanent" charge over time. How long are we talking before a significant change can be discerned? What are the effects? Lower output? Higher noise? Is there anything that can be done to slow this process?

Thanks...

They do fail over time and there's nothing you can do to slow the aging except replace them.
That's becoming even harder as fewer 'professional' electret capsules are being made or sold.
They're supposed to be stored in aluminum pouches (the way the capsules used to be sold) when not in use.
That's becoming even harder as fewer electret capsules are being made or sold.

thanks... so what happens to them, and how long does it take to show noticeably?

I asked that question about a year ago when I was considering a ksm32. No one seems to know the lifespan although 15/20 years is sometimes generally noted for the charge on most any brand.

A couple of guys who have had ksm32s for a long time responded to my question last year that their mics were still great after ten years or so,

I asked them, "but how do you KNOW what they now really sound like compared to a new ksm32". One guy said 'oh..yeah, I guess I don't know if they are deteriorating or not".

I personally just don't want to think about it, so I'm staying away from electret types.

As usual, I think it depends on how well the manufacturer made and aged the electret capsule. A graph I recall seeing on electret charge retention showed a steep initial dropoff, then a very gradual dropoff for many years. The manufacturer can pre-age the capsule (with heat and minimal time, I think) and get to the gradual part of the curve. This may have been from Sony or B&K. We are not talking about cheap capsules.

Personally, I would have no problem buying any Shure KSM or DPA (yes, I believe all DPAs are electret) and using it for 20 years. If I had any question about it, it's easy enough to compare it to other mics, or send it in. I've seen plenty of externally biased condensers like Neumanns that need some kind of major service within that time frame, too.

thanks for your responses...

There are many AT4033 that are older than that and are working just fine...
Its a DC potential with VERY VERY low load, if any at all...