I built several of these to have around the studio. They are handy when you have a huge drum kit and only a 16 track studio!! It enables you to shrink 4 toms down to 2, or 6 down to 3.
If you have multiple guitar cabs or amps, or a stereo rig like I do and you want to mike them but only have limited inputs on your mixer these come in handy as well.
You can build it as shown with three or more into one inside a small bud box, or do as I did and make "Y" cables out of a couple of mike cables.
If you want a combiner, use multiple female XLR plugs into one XLR male. For a splitter, use multiple male XLR plus into a single female XLR. Don't forget the 330R resistors, and use shrinkwrap to cover the connections.