At least two reasons:

(a) microphone signals are small compared with line levels, often 60dB lower. This means that any hum, noise and crosstalk injected into the microphone signals at the patchbay is 1000 times more significant than the same amount of noise injected into a line level signal.

(b) patchbays are usually equipped with jacks for the patching rather than XLRs. The action of plugging or unplugging a jack patchlead shorts out the signals momentarily. This is not a good idea if the circuits carry phantom power for the microphones.

On the other hand,
I've had my mics patchbay'd for years without incident.
They're normaled to the console, but can be broken out to go to outboard mic pre's. or cross patched to other channels.

I don't understand Boswell's [a] statement.
Mic's should never be patched to a line input. (via patchbay or otherwise) A mic source appearing at a patchbay, needs to be patched to a Mic Pre. There is no other place for it to logically go. (and the balanced signal will retain it's low noise integrity.)

As far as Boswell's statement. He might have a point there. But just like making sure that the control room vol is down when plugging things in, and all the other safety things that a good engineer does,(not only for your gear, but for your clients as well) you also make sure that your mic pre is not sending phantom until connections are made. And of course you always make patches in the direction of the signal flow. (From the mic patch TO the Mic Pre. Not the other way around.)

On the other, other hand, if you're a hobbist, or have a propensity to blowing things up, then a pro patchbay might not be for you.

Just make sure that they are soldered in (or use a punchblock bay) and you should be fine.

With my old vintage Neve console, from NBC-TV, my microphones are on the patch panels but beware! If you have microphones plugged in and you decide to route that microphone to another input, you can blow up and kill microphones while doing so. Especially a ribbon microphone! The 1/4" plug makes and breaks the circuit with a different time interval between connections. That's the killer. You don't have that problem when plugging in and unplugging XLR connections since they are made and broken at the same point in time.

Oxidized bronze patch cords can be a huge source of problems. So decide what you want to go where before plugging the microphone in, just to be safe and to prevent the explosions coming-out of your studio monitors which will assuredly blow those up as well if you do not lower/dim or mute your control room monitors first.

Indiscrepancies in 1/4" make/break contacts can also affect microphone impedance loading, so if you think something doesn't quite sound right, you are probably correct?

Use it at your own risk
Ms. Remy Ann David

Thanks for the insight! 8-)

natural wrote: I don't understand Boswell's [a] statement.
Mic's should never be patched to a line input. (via patchbay or otherwise) A mic source appearing at a patchbay, needs to be patched to a Mic Pre. There is no other place for it to logically go. (and the balanced signal will retain it's low noise integrity.

My post never suggested you connect mics to line ins. The point was that all interconnect schemes (such as patchbays) introduce noise into the signals passing through them. The noise can be crosstalk from other channels, hum, RF that gets demodulated or whatever, and the amount depends on the design of the patchbay and how it is installed. Since there is about 60dB more gain after a microphone patchbay than after a line-level patchbay, the introduced noise is more significant in a microphone circuit. That said, with care, microphone patchbays have their uses.