Have any of you ever recorded a grand piano from underneath it? The reason I'm asking is that I want to record a recital in which the lid to the piano has to be shut (for balance purposes in the room).
I've heard of this technique; I've done it once, but I didn't like the results.
If the lid HAS to be closed, maybe you can get a PZM mic and mount it on the underside of the lid.
Micing the underside of a piano is often done to suppliment the sound of the top mic(s) - by itself the underside mic will sound like crap. Like MJ said, a PZM taped to the lid will work, or a couple of SD condensers carefully mounted so they don't rattle against anything. It won't be an ideal situation, but better than just an underside mic.