Maybe you were reading about taking a relatively small loudspeaker and "reversing" it's role....using it as a kick drum mic instead of a loudspeaker. There were several posts talking about using the 7" woofer from a Yamaha NS10 monitor, hooking it up to a suitable transformer, and running it out into a mixer channel. You mount the speaker to a board to place it in front of the kick. It certainly picks up the low end, and has been a trick LA engineers did way back in the days of Stevie Wonders' "Songs in the Key of Life". Yamaha now makes a commercially-marketed version of that "mic"...I made one in the 80s using an 8" Utah hi-fi speaker. didn't even need a transformer to get it to work...

That's very interesting but not what I'm looking for. But what would a suitable transformer be and would you have to power it. I have heard of this method. thanks for the reply

I had a mediocre Sescom passive DI box as the transformer. Doesn't look right on paper, but it worked OK. This design is passive, so there is no power to worry about. I would definitely have the phantom power to that input of your board OFF, though.
The only other time I've seen a board with a mic on it for the kick was actually a Shure boundary mic mounted to a small piece of plywood (about a 6"x6" piece of 3/4") that was laid inside the drum, on top of a folded blanklet....