DIY snare mic

What's the mic on top of the 57? (I'm figuring a condenser of some sort?) IIRC, Audio Technica make a combo dual transducer mic along these lines.

I've yet to hear one, or otherwise employ this method, but I've always been curious, and pondered whether it would work better with a crossover inserted on the mic channels.
 
It has a very open sound and a extremely linear on and off-axis frequency response.

It's highly directional, so it's a bit "focused" in the sound with excellent transient response.

Transient sources (drums, percussion etc) is where it absolutely shines, you should give it a try if you have the opportunity.