that will change the impeadence load on the mic pre. it can work (sorta) but only do it with dynamic mics. try it and see what you get. i did it once myself with 2 57's and it worked out fine. i don't think it will work well ribbons and i know you can't do it with phantom powered condensers.

As Kurt says, you can use the technique with dynamic microphones, but they should be of the same type (e.g. both 57/58) on each input and be picking up sound sources of similar loudness.

Depending on available space and amount of sound spill, I sometimes use this method if I need closer micing of a wide instrument such as a xylophone going into a single channel. I have a small box I made many years ago that I sometimes carry with me when I'm recording at live gigs. It's got a switch to select series or parallel operation of the two microphones to give different damping factors. It's surprising what a difference switching between the two positions makes, especially if the mics are used on percussive sources such as drum kits, marimbas etc. If you just use an XLR Y-cable, you are always going to get parallel operation.

Note that Y-cables of the type you would need (2xF to M) are much less common than the other way round, as the normal splitter usage is that you send an output to two destinations.

Boswell, post: 430933, member: 29034 wrote: I have a small box I made many years ago that I sometimes carry with me when I'm recording at live gigs. It's got a switch to select series or parallel operation of the two microphones to give different damping factors.

Boswell, could you please explain how the switch is wired? This sounds like an interesting project, but I'm having a hard time envisioning how one would wire mics in series and keep them all balanced in a passive combiner. Is it still completely passive?

Think of it like a voltage-selector switch on the primary of a mains transformer that connects two windings in parallel for 120V input and puts them in series for 240V input.

The hot end of one mic goes to the output XLR hot and the cold end of the other mic goes to the output XLR cold. The cold pin of the first mic and the hot pin of the second mic go to the centre poles of a DPDT switch (slide or rotary). One end of the switch has its contacts connected together (to give series operation) and the two contacts on the other end are cross-connected to the hot and cold outputs.

In parallel mode, each mic sees the combination of the other mic (same impedance) in parallel with the pre-amp's input impedance. That means the output voltage will be about half that of using the mic on its own, but the damping factor is increased dramatically.

In series mode, each mic is driving an impedance which is the sum of the other mic and the pre-amp's input impedance. With a bridging pre-amp input, this will give approximately the same output as using a single mic, but the damping factor is reduced.

All completely passive and balanced - only the impedances are altered with corresponding effects on the output voltages and damping factors.

That's excellent, thank you. It's not nearly as complicated as I was making it.

I'm using phantom powered condensers, so I'll scratch that for now.

My audio engineering knowledge isn't at the point of knowing circuitry just yet, but it sure does sound fascinating and precise. I would probably record a xylophone like a piano to start, but I haven't done that yet so I don't know how it would sound.

Thank you kind sirs.

You can do some interesting stuff combining dynamics. If you are doing live stuff with combined 57s (and others of course). Sum and difference stuff. Two dynamics one with the polarity reversed in a crossover barrel, cancel distant sounds and let you hear things with a level difference between mics. It's weird on rack toms - spill goes down, and you get a sort of compressed thump. Interesting to play with - not really sure it's that repeatable though. I did use it once on two 58s for a vocalist who was standing right in front of a massive guitar amp. Got him to sing into one, and ignore the one taped to it. It was a bit thin sounding, but eq'd to passable.