aye. its for bassdrum sound leveling, etc. cool little toy to have, but really useless for live performances since most people use a mic in a mic hole on your bass drum and the soundman does the rest...
It's called a woofer..Don't worry about micing--you can cut a hole in the main bass drum head-then put the mic inside, either on a stand or a pillow..It hides the mic and keeps it out of sight...I have one, adds hella Bass boom!
Woof Woof...I've used them before to much delight! I usually mic my mian kick and the woofer both using the may micing system. Extra low end rumble.
Lots of dw guys use them live and in the studio. Watch Billy Wards Modern Drummer Festival weekend video.