Build A Twisted XLR Y Cable
In a normal Y cable, each of the three connectors is wired to the same pin on the other two. The Twist is that in one of the two male XLR connectors, the pin 2 and 3 connections are swapped.



As a result, the polarity of this connector is the opposite of the other connectors. This makes the following experiment possible.
First, put a couple of mikes on a snare drum, one just above the top head, the other the same distance beneath the bottom head. Listen to them both Individually, then listen to them both panned to the center at roughly equal levels.
When the two mikes are combined, the sound should be much thinner than when either mike is heard alone.
This is because the drums top head is moving away from the top mike at the same time the bottom head is moving towards the bottom mic.
When the two mikes are mixed together, this electronically cancels the main motion of the drum heads (where the low-frequency sounds are)
While its a safe bet you'll want to reverse polarity on the bottom mike, the same experiment is vaulable any time you have two mikes picking up some of the same sounds. Theres no right answer! Use your ears to decide whether you want to reverse polarity on a case by case basis.

Heres another worthwhile experiment to try: If you have a microphone that can be set to a "figure 8" or "bidirectional" pickup pattern, use it along with a second "Omni" or "Cardoid" pattern mike.
The polarity-reversing Y cable is connected to the output of the figure 8 mike and brought into a pair of channels that are both turned up, but panned to the extreme left and right. Connect the Omni or cardoid mike to a channel panned to the center.

The Omni or cardoid mic will create a strong "center" image and bringing up the two channels of the figure 8 equally will add a startling natural stereo "width" to the blend. This miking technique, called "M/S" for "Middle/Side" can be very effective on acoustic guitar, drum overheads, group vocals and even entire ensembles.

Many Thanks To the Author!