First of all, please note that different pianos sound different, have different shapes, and microphone placement will also depend on the style of music.
You are right to mic a concert grand in stereo.
Put the lid of the piano on the long stick. Place one microphone about 12 inches above the bass (longer) strings, aiming it at the string in the middle of the bass range, at a point halfway down the string (between the wrest block and the rear end of the frame).
Place another microphone about 12 inches above the treble (shorter) strings, aligning it with the string in the middle of the treble range, again at a point halfway down the string.
This technique gives a very natural, well-balanced piano sound. Do not point the microphones at the middle of the instrument as you would lose some of the high and low end sound. We have found that the C 535 is an excellent choice for this miking technique.
In live situations where you may have to fight bleeding from other instruments or feedback problems, you can place the mics closer to the strings. Note that you will get a different sound with the microphones at closer range.
On a noisy stage, you may even need to close the lid of the grand piano, but again this will change the sound dramatically and you should experiment with microphone placement. While the C 411 gives good results in this application, the C 516 or C 519 will provide an even better sound.
Alternatively, you can tape boundary microphones such as the C 547 BL to the lid before closing it. Align them with the bass and treble strings as described above.
In some cases, a monitoring signal derived from the two stereo microphones may not be loud enough. In this case, you should add a dynamic mic close to the treble strings.
