From SimpsonDan@aol.com Tue Jun 05 08:10:30 2001
Subject:Re: mic wiring

I'm wiring up the 2 mics I got from from Mouser to a female XLR for the Pro3T.>

No such thing as a stupid question, Dean, and this one is actually pretty complicated.

I'm sure there are others on this board with more electronics experience who can provide a better explanation (Bruce, for sure), but I'll take a first shot.

An XLR is a three-pin connector: Pin 1 (on the upper right on the female connector, the upper left on the male connector) is the ground. Pin 2 (the other side) is the hot signal (at least in new gear) and pin 3 (at the bottom) is the cold. Most mics, though not all, are balanced, which means that Pin 2 contains the hot signal and pin 3 contains a phase-inverted copy of the same signal. The benefits are a 3dB increase in overall gain and what is called common mode rejection. Any noise that enters the cable gets canceled at the input since the phase relationships of the two signals are opposite.

It is a bad idea to try to wire two mics to a single XLR. Bruce and others can probably provide the technical rational, which is going to involve impedance problems, among others, but I can tell you that it is not going to work. A Y cable is not going to make it any better.

If you have two mics you have to connect them to 2 separate XLRs and then use the mixer to combine the signals. If you only have one inpuit on the board, then you are *FAR* better off with a single mic than trying to rig up anything with two mics into a single XLR.

Bruce, can you add (or subtract) to this cryptic explanation? You are the expert in the physics of this stuff.

Dan