Whether it's on stage or in the recording studio, setting up the microphones to capture the sound of your drums can be really tricky. The problem is that every microphone you use actually hears some of the sound from every part of the kit, so you're bound to get plenty of the snare drum sound in your tom tom mics etcetera. This sonic bleeding between the microphones makes it tricky to get a clean dynamic sound.
To fix the problem, Sennheiser has invented a system that only opens up the mic channel for a particular drum, when that drum has been hit by the drum sticks. Best of all, to make that determination, they're using frikkin' lasers. A laser positioned over the drum head reflects off the surface of the drum, and this reflection is read by a sensor. When the drum vibrates from being struck, the laser reflection shifts away from the sensor, triggering something called a noise gate that turns on the microphone's signal. This way each microphone only works when it's associated drum is being struck, eliminating the confusing background noise from the other drums.
Check out the video to see the Sennheiser Element laser gating system in action. The video was made for audio professionals so it does get a bit technical, but I think you'll get the concept.
Via Pro Sound Web