Re: Two pianos, one microphone
OK, maybe I'll be third time lucky trying to reply to this thread. 
~~:smile:
The two sides of a figure-8 mic are indeed out of polarity with each other. A sound arriving at 90° off axis enters both sides equally, and is cancelled out. A ribbon mic does this mechanically. A condenser like a C-414, has two diaphragms back to back. In Figure-8 mode, the front diaphragm is polarized with +60V, the back is at -60V. A sound at 90° is cancelled electrically. For an omni pattern both sides are polarized at +60V. You can get any intermediate pattern by polarizing the back diaphragm at a voltage between -60 and +60V. Grounding the back gives you a cardioid pattern.
I've used a single C-414 in figure-8 before to mic a grand piano with decent results. It was set up above the hammers, one side facing left, and the other right. It was just a matter of finding the spot that gave the desired balance between high and low notes.
GTD
